revision: --include-diversions adds helpful merges
PATCH 1/1 revision: --include-diversions adds helpful merges
From: Derrick Stolee <[email protected]>
The default file history simplification of "git log -- <path>" or "git rev-list -- <path>" focuses on providing the smallest set of commits that first contributed a change. The revision walk greatly restricts the set of walked commits by visiting only the first TREESAME parent of a merge commit, when one exists. This means that portions of the commit-graph are not walked, which can be a performance benefit, but can also "hide" commits that added changes but were ignored by a merge resolution.
The --full-history option modifies this by walking all commits and reporting a merge commit as "interesting" if it has _any_ parent that is not TREESAME. This tends to be an over-representation of important commits, especially in an environment where most merge commits are created by pull request completion.
Suppose we have a commit A and we create a commit B on top that changes our file. When we merge the pull request, we create a merge commit M. If no one else changed the file in the first-parent history between M and A, then M will not be TREESAME to its first parent, but will be TREESAME to B. Thus, the simplified history will be "B". However, M will appear in the --full-history mode.
However, suppose that a number of topics T1, T2, ..., Tn were created based on commits C1, C2, ..., Cn between A and M as follows:
A----C1----C2--- ... ---Cn----M------P1---P2--- ... ---Pn
\ \ \ \ / / / /
\ \__.. \ \/ ..__T1 / Tn
\ \__.. /\ ..__T2 /
\_____________________B \____________________/If the commits T1, T2, ... Tn did not change the file, then all of P1 through Pn will be TREESAME to their first parent, but not TREESAME to their second. This means that all of those merge commits appear in the --full-history view, with edges that immediately collapse into the lower history without introducing interesting single-parent commits.
The --simplify-merges option was introduced to remove these extra merge commits. By noticing that the rewritten parents are reachable from their first parents, those edges can be simplified away. Finally, the commits now look like single-parent commits that are TREESAME to their "only" parent. Thus, they are removed and this issue does not cause issues anymore. However, this also ends up removing the commit M from the history view! Even worse, the --simplify-merges option requires walking the entire history before returning a single result.
Many Git users are using Git alongside a Git service that provides code storage alongside a code review tool commonly called "Pull Requests" or "Merge Requests" against a target branch. When these requests are accepted and merged, they typically create a merge commit whose first parent is the previous branch tip and the second parent is the tip of the topic branch used for the request. This presents a valuable order to the parents, but also makes that merge commit slightly special. Users may want to see not only which commits changed a file, but which pull requests merged those commits into their branch. In the previous example, this would mean the users want to see the merge commit "M" in addition to the single- parent commit "C".
Users are even more likely to want these merge commits when they use pull requests to merge into a feature branch before merging that feature branch into their trunk.
In some sense, users are asking for the "first" merge commit to bring in the change to their branch. As long as the parent order is consistent, this can be handled with the following rule:
Include a merge commit if it is not TREESAME to its first parent, but is TREESAME to a later parent.
I call such merge commits "diversions" because they divert the history walk away from the first-parent history. As such, this change adds the "--include-diversions" option to rev-list and log. To test these options, extend the standard test example to include a merge commit that is not TREESAME to its first parent. It is surprising that that option was not already in the example, as it is instructive.
In particular, this extension demonstrates a common issue with file history simplification. When a user resolves a merge conflict using "-Xours" or otherwise ignoring one side of the conflict, they create a TREESAME edge that probably should not be TREESAME. This leads users to become frustrated and complain that "my change disappeared!" In my experience, showing them history with --full-history and --simplify-merges quickly reveals the problematic merge. As mentioned, this option is expensive to compute. The --include-diversions option _might_ show the merge commit (usually titled "resolving conflicts") more quickly. Of course, this depends on the user having the correct parent order, which is backwards when using "git pull".
---
Add a new history mode
This --include-diversions option could use a better name.
An experienced developer in the Windows OS Engineering Systems team pointed out how hard it is to find out when a change was "introduced" in the Windows OS repo. Due to their multi-leveled, long-lived branch organization, a commit could be part of hundreds of pull requests as the branches are merged across the organization.
My default answer was "this is complicated not because of Git, but because of how you are branching." I then tried to explain how finding the "first merge" to include a commit is incredibly difficult and requires performing multiple reachability queries. As I was working it out on paper, I realized that was true if we relied only on the commit-graph shape to inform our qurey.
If we use the TREESAME information, then suddenly we get a much clearer picture! Let's simply pick out those merge commits that "introduced a change" because they are TREESAME to a non-first-parent (and not TREESAME to the first parent).
My name of "diversions" could probably use some work, but I like the basic concept of this option.
I welcome any and all feedback. Thanks!
-Stolee
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-599%2Fderrickstolee%2Fnew-history-mode-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-599/derrickstolee/new-history-mode-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/599
Documentation/rev-list-options.txt | 6 ++++ revision.c | 16 ++++++++++- revision.h | 1 + t/t6012-rev-list-simplify.sh | 44 ++++++++++++++++++++++++++++++ 4 files changed, 66 insertions(+), 1 deletion(-)
Documentation/rev-list-options.txt +6 -0
@@ -342,6 +342,12 @@ Default mode:: branches if the end result is the same (i.e. merging branches with the same content) +--include-diversions:: + Include all commits from the default mode, but also any merge + commits that are not TREESAME to the first parent but are + TREESAME to a later parent. This mode is helpful for showing + the merge commits that "first introduced" a change to a branch. + --full-history:: Same as the default mode, but does not prune some history.
revision.c +15 -1
@@ -870,7 +870,19 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) } parent->next =NULL ; commit->parents = parent; - commit->object.flags |=TREESAME ; + +/* +* A merge commit is a "diversion" if it is not +* TREESAME to its first parent but is TREESAME +* to a later parent. In the simplified history, +* we "divert" the history walk to the later +* parent. These commits are shown when "diversions" +* is enabled, so do not mark the object as +* TREESAME here. +*/ +if (!revs->diversions || !nth_parent) + commit->object.flags |=TREESAME ; +return ;case REV_TREE_NEW :
@@ -2265,6 +2277,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg }else if (!strcmp (arg,"--full-diff" )) { revs->diff =1 ; revs->full_diff =1 ; + }else if (!strcmp (arg,"--include-diversions" )) { + revs->diversions =1 ; }else if (!strcmp (arg,"--full-history" )) { revs->simplify_history =0 ; }else if (!strcmp (arg,"--relative-date" )) {
revision.h +1 -0
@@ -129,6 +129,7 @@ struct rev_info { no_walk:2, remove_empty_trees:1, simplify_history:1, + diversions:1, topo_order:1, simplify_merges:1, simplify_by_decoration:1,
t/t6012-rev-list-simplify.sh +44 -0
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base-commit: 274b9cc25322d9ee79aa8e6d4e86f0ffe5ced925
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gitgitgadget
Quoted 1 line · Derrick Stolee via GitGitGadget
This --include-diversions option could use a better name.
True, but I do not think of a better (or for that matter a worse) one.
As a new feature, I think this is a reasonable thing to want, especially it is in line with the push in the past few years to treat the first parent history specially.
I wonder how this would interact with the ancestry-path option? That one also, like the simplify-merges option, needs a limited traversal, and if this new mode can do without a limited traversal (in other words, the output can be done incrementally from the tip) and achieve something similar to what these other options wanted to show, that would be great.
Thanks.
Quoted 11 lines · Junio C Hamano
Quoted 1 line · Derrick Stolee via GitGitGadget
This --include-diversions option could use a better name.
True, but I do not think of a better (or for that matter a worse) one.
As a new feature, I think this is a reasonable thing to want, especially it is in line with the push in the past few years to treat the first parent history specially.
Quoted 6 lines
I wonder how this would interact with the ancestry-path option? That one also, like the simplify-merges option, needs a limited traversal, and if this new mode can do without a limited traversal (in other words, the output can be done incrementally from the tip) and achieve something similar to what these other options wanted to show, that would be great.
You're right. I briefly considered the --ancestry-path option before realizing that would get a huge set of commits (for example: every topic based on the branch after the pull request was merged).
The --include-diversions works incrementally like simplified merges. Based on the implementation, it would not change the results when added to a --full-history query. This makes sense: a diversion would appear in the --full-history results, anyway.
It is worth adding tests for the combination with --ancestry-path and --simplify-merges, as the --include-diversions option would add results to those queries.
Thanks,
-Stolee
Quoted 7 lines · Derrick Stolee
Quoted 6 lines · Junio C Hamano
Quoted 1 line · Derrick Stolee via GitGitGadget
This --include-diversions option could use a better name.
True, but I do not think of a better (or for that matter a worse) one.
Here are some alternative names:
--audit-merges
--audit-trunk
--first-merges
--subtle-merges
--more-merges
The "audit" name implies some of the intent: we are trying to audit which merge commits introduced these changes. The --audit-trunk implies we are using a trunk-based workflow where parent order is critical. However, "trunk" may be confusing when there are multiple long-lived branches.
A "first merge" is confusing when we see a sequence of multiple diversion merges (I include a test with this exact situation in my next version.)
"subtle" is a bit wishy-washy.
"--more-merges" is not very specific. The way we are adding merges to the final result may not be the only way we want to add "more" merges in the future.
So, I think "--audit-merges" is the best of these alternatives. I'd be happy to be overruled with a different option. Hopefully, these options inspire better ideas from the community.
Quoted 15 lines
Quoted 10 lines
As a new feature, I think this is a reasonable thing to want, especially it is in line with the push in the past few years to treat the first parent history specially.
I wonder how this would interact with the ancestry-path option? That one also, like the simplify-merges option, needs a limited traversal, and if this new mode can do without a limited traversal (in other words, the output can be done incrementally from the tip) and achieve something similar to what these other options wanted to show, that would be great.
You're right. I briefly considered the --ancestry-path option before realizing that would get a huge set of commits (for example: every topic based on the branch after the pull request was merged).
Quoted 8 lines
The --include-diversions works incrementally like simplified merges. Based on the implementation, it would not change the results when added to a --full-history query. This makes sense: a diversion would appear in the --full-history results, anyway.
It is worth adding tests for the combination with --ancestry-path and --simplify-merges, as the --include-diversions option would add results to those queries.
My gitgitgadget PR [1] is updated with tests and some new logic to handle the new option along with --simplify-merges. The situation was a bit subtle, so my next version will include a significant update to the rev-list documentation under the "History Simplification" mode.
I'll give things some time to calm on the name of the option before sending a v2.
My v2 also includes adding a new object flag "DIVERSION" to track these commits from the TREESAME calculation through the simplify-merges logic. When I was adding a new flag, I realized that I already messed up the 32-bit alignment of "struct object" when adding the TOPO_ORDER flags. The parsed, type, and flags bitfields add up to 33 bits!
A solution would include pulling the TOPO_ORDER_* flags to be bits 22 and 23 instead of 26 and 27, but that would collide with what is happening in builtin/show-branch.c. But then I saw the following comment in builtin/show-branch.c:
/*
* TODO: convert this use of commit->object.flags to commit-slab
* instead to store a pointer to ref name directly. Then use the same
* UNINTERESTING definition from revision.h here.
*/
Is anyone interested in tackling this problem? I don't see any test failures when I swap the TOPO_ORDER_ flag locations, but that might just mean that show-branch isn't tested enough.
Thanks,
-Stolee
Quoted 17 lines · Derrick Stolee
Quoted 7 lines · Derrick Stolee
Quoted 6 lines · Junio C Hamano
Quoted 1 line · Derrick Stolee via GitGitGadget
This --include-diversions option could use a better name.
True, but I do not think of a better (or for that matter a worse) one.
Here are some alternative names:
--audit-merges
--audit-trunk
--first-merges
--subtle-merges
--more-merges
Quoted 5 lines
The "audit" name implies some of the intent: we are trying to audit which merge commits introduced these changes. The --audit-trunk implies we are using a trunk-based workflow where parent order is critical. However, "trunk" may be confusing when there are multiple long-lived branches.
Our features written with the intent to be useful for one purpose often end up being used for purposes other than what the feature was originally written for (the "--pickaxe" has always been a bitter example of this for me).
For that reason, I am a bit hesitant to endorse "audit" exactly because of the implication of "intent".
We usually try to give a single simplest history that explains how the current content in the path came to be. For that, commit M in the illustration in your original message does not really help when we ignore which parent chain owns the history, but in practice, many workflows treat the first parent chain as something special, so we want to show, not just the individual changes that matter, where the changes are introduced in the first-parent chain.
I wonder if there is a simple-enough phrase to convey what the latter half of above sentence says. "include" and "keep" are both good verbs---normally we discard these merges, because they do not contribute at the level of individual changes, but with the option, we "include" or "keep" these merges in the output. It's not like we keep _all_ the merges, but selected merges only. How do we decide which merges to keep?
I guess your "--first-merges" came from such a line of thought, and is the closest among the five to what I have in mind, but it drops too many words and loses too much meaning.
"--keep-first-parent-merges", perhaps?
Quoted 7 lines · Junio C Hamano
Our features written with the intent to be useful for one purpose often end up being used for purposes other than what the feature was originally written for (the "--pickaxe" has always been a bitter example of this for me).
For that reason, I am a bit hesitant to endorse "audit" exactly because of the implication of "intent".
Yeah, I agree with this.
Quoted 8 lines
I wonder if there is a simple-enough phrase to convey what the latter half of above sentence says. "include" and "keep" are both good verbs---normally we discard these merges, because they do not contribute at the level of individual changes, but with the option, we "include" or "keep" these merges in the output. It's not like we keep _all_ the merges, but selected merges only. How do we decide which merges to keep?
Quoted 5 lines
I guess your "--first-merges" came from such a line of thought, and is the closest among the five to what I have in mind, but it drops too many words and loses too much meaning.
"--keep-first-parent-merges", perhaps?
FWIW, this name left me more confused, because "first-parent merges" isn't an already-defined term I knew. And it seems like all merges have a first parent. Having read the patch description, I guess it's "a merge which isn't TREESAME to its first-parent".
I can't think of a more succinct way to name that, though. And possibly if we gave that definition in the documentation, that would be enough. The name doesn't have to be a complete description; it only has to make sense once you know what you're trying to do (and be memorable enough).
-Peff
Quoted 31 lines · Jeff King
Quoted 7 lines · Junio C Hamano
Our features written with the intent to be useful for one purpose often end up being used for purposes other than what the feature was originally written for (the "--pickaxe" has always been a bitter example of this for me).
For that reason, I am a bit hesitant to endorse "audit" exactly because of the implication of "intent".
Yeah, I agree with this.
Quoted 8 lines
I wonder if there is a simple-enough phrase to convey what the latter half of above sentence says. "include" and "keep" are both good verbs---normally we discard these merges, because they do not contribute at the level of individual changes, but with the option, we "include" or "keep" these merges in the output. It's not like we keep _all_ the merges, but selected merges only. How do we decide which merges to keep?
Quoted 5 lines
I guess your "--first-merges" came from such a line of thought, and is the closest among the five to what I have in mind, but it drops too many words and loses too much meaning.
"--keep-first-parent-merges", perhaps?
FWIW, this name left me more confused, because "first-parent merges" isn't an already-defined term I knew. And it seems like all merges have a first parent. Having read the patch description, I guess it's "a merge which isn't TREESAME to its first-parent".
Quoted 4 lines
I can't think of a more succinct way to name that, though. And possibly if we gave that definition in the documentation, that would be enough. The name doesn't have to be a complete description; it only has to make sense once you know what you're trying to do (and be memorable enough).
Then I suppose we should focus on naming merge commits with this property:
A merge commit that is not TREESAME to its first parent (but is TREESAME to a later parent).
The part in parentheses may be optional, because a merge commit that is not TREESAME to any parent will be included by every history mode.
In my latest attempt at documentation, I called these merges "diverters" yet still used "--include-diversions". Here are a few other words that we could use:
* diverters or diversions
* redirects
* switches (think railroad switch). Synonym: exchange
* detours
The "switch" or "exchange" words are probably bad because they have noun _and_ verb forms.
Or we could look again at the history results as a whole to find inspiration for the command-line option:
* --merge-trail
Thanks,
-Stolee
Quoted 7 lines · Derrick Stolee
Then I suppose we should focus on naming merge commits with this property:
A merge commit that is not TREESAME to its first parent (but is TREESAME to a later parent).
The part in parentheses may be optional, because a merge commit that is not TREESAME to any parent will be included by every history mode.
A merge that is TREESAME to its first parent does not introduce anything new to the mainline (as far as the paths that match the pathspec are concerned). We are trying to find names to call merges that are not those no-op merges. Hmph...
Quoted 8 lines
In my latest attempt at documentation, I called these merges "diverters" yet still used "--include-diversions". Here are a few other words that we could use:
* diverters or diversions
* redirects
* switches (think railroad switch). Synonym: exchange
* detours
...none of the above tells me that they are not no-op (in other words, they do something meaningful), so I must be coming from a direction different from you are. What redirects from what other thing, for example?
Quoted 7 lines · Junio C Hamano
Quoted 5 lines · Derrick Stolee
Then I suppose we should focus on naming merge commits with this property:
A merge commit that is not TREESAME to its first parent (but is TREESAME to a later parent).
Quoted 7 lines
Quoted 2 lines
The part in parentheses may be optional, because a merge commit that is not TREESAME to any parent will be included by every history mode.
A merge that is TREESAME to its first parent does not introduce anything new to the mainline (as far as the paths that match the pathspec are concerned). We are trying to find names to call merges that are not those no-op merges. Hmph...
There are three situations for a merge commit:
1. TREESAME to _all_ parents. These are not included.
2. not TREESAME to _all_ parents. These are already included.
3. TREESAME to some, but not TREESAME to others.
The third mode is the one that default mode will drop, but --full-history will include. The new mode will include some of these (the ones that are NOT TREESAME to their first parent).
Quoted 9 lines
Quoted 8 lines
In my latest attempt at documentation, I called these merges "diverters" yet still used "--include-diversions". Here are a few other words that we could use:
* diverters or diversions
* redirects
* switches (think railroad switch). Synonym: exchange
* detours
Quoted 4 lines
...none of the above tells me that they are not no-op (in other words, they do something meaningful), so I must be coming from a direction different from you are. What redirects from what other thing, for example?
The merges do something meaningful: they "merge in" a "real" change.
I'll just submit my v2 as-is, which includes a significant change to the documentation that should make things more clear.
Thanks,
-Stolee
Quoted 9 lines · Derrick Stolee
Quoted 9 lines
Quoted 8 lines
In my latest attempt at documentation, I called these merges "diverters" yet still used "--include-diversions". Here are a few other words that we could use:
* diverters or diversions
* redirects
* switches (think railroad switch). Synonym: exchange
* detours
Quoted 6 lines
Quoted 4 lines
...none of the above tells me that they are not no-op (in other words, they do something meaningful), so I must be coming from a direction different from you are. What redirects from what other thing, for example?
The merges do something meaningful: they "merge in" a "real" change.
Yes, but "redirect", "switch", "detour", or "divert" do not quite mean "merging in a real change", at least to me.
Quoted 2 lines
I'll just submit my v2 as-is, which includes a significant change to the documentation that should make things more clear.
Thanks.
Quoted 16 lines · Junio C Hamano
Quoted 14 lines · Derrick Stolee
Quoted 13 lines
Quoted 8 lines
In my latest attempt at documentation, I called these merges "diverters" yet still used "--include-diversions". Here are a few other words that we could use:
* diverters or diversions
* redirects
* switches (think railroad switch). Synonym: exchange
* detours...none of the above tells me that they are not no-op (in other words, they do something meaningful), so I must be coming from a direction different from you are. What redirects from what other thing, for example?
Quoted 4 lines
Quoted 1 line
The merges do something meaningful: they "merge in" a "real" change.
Yes, but "redirect", "switch", "detour", or "divert" do not quite mean "merging in a real change", at least to me.
Makes sense to me. The way you explain why certain words don't work for you helps me think of new words to describe these merges:
* signposts
* guides
* signals
For the argument, we cwould add "-merge" to each of these, such as "--signpost-merges" or "--signal-merges".
I'm going to keep replying to this thread with ideas until someone says "This one makes sense to me" or an equivalent. Alternatively, someone else could present an idea and then I get to say "Aha! That captures this concept clearly with an obvious metaphor!"
Thanks,
-Stolee
Hi
Quoted 14 lines · Junio C Hamano
Quoted 12 lines · Derrick Stolee
Quoted 12 lines
Quoted 8 lines
In my latest attempt at documentation, I called these merges "diverters" yet still used "--include-diversions". Here are a few other words that we could use:
* diverters or diversions
* redirects
* switches (think railroad switch). Synonym: exchange
* detours...none of the above tells me that they are not no-op (in other words, they do something meaningful), so I must be coming from a direction different from you are. What redirects from what other thing, for example?
Quoted 7 lines
Quoted 1 line
The merges do something meaningful: they "merge in" a "real" change.
Yes, but "redirect", "switch", "detour", or "divert" do not quite mean "merging in a real change", at least to me.
Quoted 2 lines
I'll just submit my v2 as-is, which includes a significant change to the documentation that should make things more clear.
Thanks.
Can I suggest "--side-merges" as a possible descriptor for these non-mainline diversions?
My thesaurus had suggested detour and sidetracked, which led to the side-merge view.
Philip
Quoted 11 lines · Philip Oakley
Quoted 6 lines
Yes, but "redirect", "switch", "detour", or "divert" do not quite mean "merging in a real change", at least to me.
Quoted 2 lines
I'll just submit my v2 as-is, which includes a significant change to the documentation that should make things more clear.
Thanks.
Can I suggest "--side-merges" as a possible descriptor for these non-mainline diversions?
My thesaurus had suggested detour and sidetracked, which led to the side-merge view.
Ahh, sorry Derrick for being slow and thanks Philip for repeating "diversion", as the word did not click for me at all when I saw the patch and wrote my response.
But I think it started slowly to dawn on me.
Does it come from the worldview where we want to follow the "trunk" but because when we notice at a merge that we got everything that matters to us from a side branch, we switch the track out of the mainline and from then on follow that side branch? Switching the track and following the side branch happens silently with the default "history simplification", but the new feature shows where that side-tracking happens more prominently---is that where the words "divert" etc. come from?
Then I can understand how these candidate words may have place in describing the situation we want to use the feature; I am not yet convinced any of the concrete option names floated on the thread (or what I can come up with right now) would be clear to our target audiences, but at least I am not as confused as I was before.
Thanks.
Quoted 29 lines · Junio C Hamano
Quoted 11 lines · Philip Oakley
Quoted 6 lines
Yes, but "redirect", "switch", "detour", or "divert" do not quite mean "merging in a real change", at least to me.
Quoted 2 lines
I'll just submit my v2 as-is, which includes a significant change to the documentation that should make things more clear.
Thanks.
Can I suggest "--side-merges" as a possible descriptor for these non-mainline diversions?
My thesaurus had suggested detour and sidetracked, which led to the side-merge view.
Ahh, sorry Derrick for being slow and thanks Philip for repeating "diversion", as the word did not click for me at all when I saw the patch and wrote my response.
But I think it started slowly to dawn on me.
Does it come from the worldview where we want to follow the "trunk" but because when we notice at a merge that we got everything that matters to us from a side branch, we switch the track out of the mainline and from then on follow that side branch? Switching the track and following the side branch happens silently with the default "history simplification", but the new feature shows where that side-tracking happens more prominently---is that where the words "divert" etc. come from?
Quoted 5 lines
Then I can understand how these candidate words may have place in describing the situation we want to use the feature; I am not yet convinced any of the concrete option names floated on the thread (or what I can come up with right now) would be clear to our target audiences, but at least I am not as confused as I was before.
After thinking about all the great responses here, and having a chat with Dscho about this, then taking a break, I had an "Aha!" moment. We should call this option:
--show-pulls
The direction here is important. Let's look at a potential "git log --graph --oneline" output to explore this idea:
* (master) A |\ | * (feature) B | |\ | | * (topic) C | | |\ | | | | | | * | D | | | | | * | | E | | | | * | | | F | |_|/ |/| | * | | G |/ / * / H |/ * I
I use (master), (feature), and (topic) to decorate branches that are updated only by "git commit" or "git pull". The file 'foo' was created by commit I.
In this graph, the single-parent commits G and D change 'foo'. The commit G enters master using "git commit".
The commit G enters topic using "git pull" starting from D. The developer on that branch resolves conflicts by taking the version of 'foo' from D. Thus C is TREESAME to D but not G.
The commit B is created by running "git pull topic" from the feature branch.
The commit A is created by running "git pull feature" from the master branch.
Thus, A and B "pulled" the change into their branches. The commit C "pulled" G into the branch, but did not keep the change to 'foo'.
Thus 'git log --graph --oneline master -- foo' would output:
* D
* I
'git log --graph --oneline --show-pulls master -- foo' shows:
* A
* B
* D
* I
'git log --graph --oneline --full-history -- foo' shows:
* (master) A |\ | * (feature) B | |\ | | * (topic) C | | |\ | | | | | | * | D | |_|/ |/| | * | | G |/ / | / |/ * I
'git log --graph --oneline --full-history --simplify-merges -- foo' would show:
* C |\ * | D | | | * G |/ * I
'git log --graph --oneline --full-history --simplify-merges --show-pulls -- foo' would show:
* A
* B
* C
|\
* | D
| |
| * G
|/
* I
In conclusion, I think "--show-pulls" provides the right context for these extra merges to show in the history view. It also roots these merges in a Git-native name (that also happens to evoke the "pull request" concept that is _not_ native to Git).
What do you think?
Thanks,
-Stolee
Quoted 6 lines · Derrick Stolee
In conclusion, I think "--show-pulls" provides the right context for these extra merges to show in the history view. It also roots these merges in a Git-native name (that also happens to evoke the "pull request" concept that is _not_ native to Git).
What do you think?
Yeah, after reading more of the thread, I think the simplest way to think about is "keep merges that pulled in something" with the implication of "(even if the other side didn't touch anything)".
And "something you pulled" is a sensible way to think of that. So --show-pulls makes sense to me. Or if we really want to tie it in to simplification, --no-simplify-pulls. But that's more awkward to type, and none of the existing simplification options use the word simplify. ;)
-Peff
Quoted 7 lines · Jeff King
Quoted 5 lines · Derrick Stolee
In conclusion, I think "--show-pulls" provides the right context for these extra merges to show in the history view. It also roots these merges in a Git-native name (that also happens to evoke the "pull request" concept that is _not_ native to Git).
Quoted 5 lines
Quoted 1 line
What do you think?
Yeah, after reading more of the thread, I think the simplest way to think about is "keep merges that pulled in something" with the implication of "(even if the other side didn't touch anything)".
Isn't it more like "even if our side didn't touch anything", though?
If a merge pulled in something, the other side by definition did something (i.e. what was pulled in); if we did something since they forked, we would have shown the merge without this patch---the only new behaviour we are adding is to show the merge even when our side didn't touch since they forked---so far we never showed that merge, but now with this option we would when we are asked to.
I agree that "this is showing pulls" is an easy way to explain.
Quoted 4 lines
And "something you pulled" is a sensible way to think of that. So --show-pulls makes sense to me. Or if we really want to tie it in to simplification, --no-simplify-pulls. But that's more awkward to type, and none of the existing simplification options use the word simplify. ;)
;-)
Quoted 7 lines · Junio C Hamano
Quoted 7 lines · Derrick Stolee
Quoted 6 lines
In conclusion, I think "--show-pulls" provides the right context for these extra merges to show in the history view. It also roots these merges in a Git-native name (that also happens to evoke the "pull request" concept that is _not_ native to Git).
Quoted 7 lines
Quoted 5 lines
Quoted 1 line
What do you think?
Yeah, after reading more of the thread, I think the simplest way to think about is "keep merges that pulled in something" with the implication of "(even if the other side didn't touch anything)".
Isn't it more like "even if our side didn't touch anything", though?
I meant the _other_ other. :) I.e., the other one that is not what just got pulled in. Which is the first parent. ;)
So yes, I think we are on the same page, and I just said it badly. Using "our side" is better than trying to double-negate "other".
-Peff
Quoted 8 lines · Derrick Stolee via GitGitGadget
The --simplify-merges option was introduced to remove these extra merge commits. By noticing that the rewritten parents are reachable from their first parents, those edges can be simplified away. Finally, the commits now look like single-parent commits that are TREESAME to their "only" parent. Thus, they are removed and this issue does not cause issues anymore. However, this also ends up removing the commit M from the history view! Even worse, the --simplify-merges option requires walking the entire history before returning a single result.
I was not aware --simplify-merges required walking the entire history. Now I know why my alias using it performs so poorly on $HUGE_REPOSITORY with thousands of extra backmerges at $DAYJOB.
Thanks for teaching me something.
Quoted 4 lines
Many Git users are using Git alongside a Git service that provides code storage alongside a code review tool commonly called "Pull Requests" or "Merge Requests" against a target branch. When these requests are accepted and merged, they typically create a merge
Quoted 8 lines
commit whose first parent is the previous branch tip and the second parent is the tip of the topic branch used for the request. This presents a valuable order to the parents, but also makes that merge commit slightly special. Users may want to see not only which commits changed a file, but which pull requests merged those commits into their branch. In the previous example, this would mean the users want to see the merge commit "M" in addition to the single- parent commit "C".
I should not hesitate to point out that this history is also true of the Git Project's repository, although of course the merges may be of less interest here.
Quoted 15 lines
In some sense, users are asking for the "first" merge commit to bring in the change to their branch. As long as the parent order is consistent, this can be handled with the following rule:
Include a merge commit if it is not TREESAME to its first parent, but is TREESAME to a later parent.
I call such merge commits "diversions" because they divert the history walk away from the first-parent history. As such, this change adds the "--include-diversions" option to rev-list and log. To test these options, extend the standard test example to include a merge commit that is not TREESAME to its first parent. It is surprising that that option was not already in the example, as it is instructive.
Quoted 11 lines
In particular, this extension demonstrates a common issue with file history simplification. When a user resolves a merge conflict using "-Xours" or otherwise ignoring one side of the conflict, they create a TREESAME edge that probably should not be TREESAME. This leads users to become frustrated and complain that "my change disappeared!" In my experience, showing them history with --full-history and --simplify-merges quickly reveals the problematic merge. As mentioned, this option is expensive to compute. The --include-diversions option _might_ show the merge commit (usually titled "resolving conflicts") more quickly. Of course, this depends on the user having the correct parent order, which is backwards when using "git pull".
I can't comment on the contents of the patch, since I'm really not at all familiar with the revision machinery, but I do think this change is a good idea. I see this as a very common use case, and I think this commit message explains the rationale well.
Quoted 5 lines
Signed-off-by Derrick Stolee <[email protected]>---
Add a new history modeThis --include-diversions option could use a better name.
As we all know, I'm terrible at naming things, so I have no suggestions here. I'm happy with the name as it stands, but am of course open to other ideas.
Documentation/rev-list-options.txt Default mode:: · line 349
Quoted 13 lines
Documentation/rev-list-options.txt +5
-0@@ -342,6 +342,12 @@ Default mode:: branches if the end result is the same (i.e. merging branches with the same content) +--include-diversions:: + Include all commits from the default mode, but also any merge + commits that are not TREESAME to the first parent but are + TREESAME to a later parent. This mode is helpful for showing + the merge commits that "first introduced" a change to a branch.
I wasn't sure if this use of "TREESAME" would be confusing, but it looks like we already use it extensively throughout the documentation, so it's probably fine.
Signature · 2 lines
brian m. carlson: Houston, Texas, US OpenPGP: https://keybase.io/bk2204
Quoted 9 lines · Derrick Stolee via GitGitGadget
The default file history simplification of "git log -- <path>" or "git rev-list -- <path>" focuses on providing the smallest set of commits that first contributed a change. The revision walk greatly restricts the set of walked commits by visiting only the first TREESAME parent of a merge commit, when one exists. This means that portions of the commit-graph are not walked, which can be a performance benefit, but can also "hide" commits that added changes but were ignored by a merge resolution.
[...]
Thanks for a really great description of the problem.
Playing around with the patch, I found one curiosity. Try this:
git log --graph --oneline origin -- GIT-VERSION-GEN >old
git log --graph --oneline --include-diversions \
origin -- GIT-VERSION-GEN >new
diff -u old newThe first hunk has:
@@ -70,6 +70,7 @@
* 20769079d2 Git 2.12-rc2
* 5588dbffbd Git 2.12-rc1
* 6e3a7b3398 Git 2.12-rc0
+* 0a45050a14 Merge branch 'rj/git-version-gen-do-not-force-abbrev'
* a7659747c2 GIT-VERSION-GEN: do not force abbreviation length used by 'describe'
* 8d7a455ed5 Start post 2.11 cycle
* 454cb6bd52 Git 2.11
which makes sense. That merge brought in a7659747c2, and the other side hadn't touched it. But I can't tell from the output how the two are related. Nor can I just add "-p" to the invocation; after we've simplified, it has only a single parent, but it's TREESAME to that parent. So it has no diff.
I actually think the most descriptive output here would be something like:
* 6e3a7b3398 Git 2.12-rc0
* 0a45050a14 Merge branch 'rj/git-version-gen-do-not-force-abbrev'
|\ | * a7659747c2 GIT-VERSION-GEN: do not force abbreviation length used by 'describe' |/
* Start post 2.11 cycle
I.e., leaving both parents intact for a "diversion" merge. But maybe that would have secondary effects in other places.
-Peff
PATCH v2 1/1 revision: --include-diversions adds helpful merges
In reply to Derrick Stolee via GitGitGadgetFrom: Derrick Stolee <[email protected]>
The default file history simplification of "git log -- <path>" or "git rev-list -- <path>" focuses on providing the smallest set of commits that first contributed a change. The revision walk greatly restricts the set of walked commits by visiting only the first TREESAME parent of a merge commit, when one exists. This means that portions of the commit-graph are not walked, which can be a performance benefit, but can also "hide" commits that added changes but were ignored by a merge resolution.
The --full-history option modifies this by walking all commits and reporting a merge commit as "interesting" if it has _any_ parent that is not TREESAME. This tends to be an over-representation of important commits, especially in an environment where most merge commits are created by pull request completion.
Suppose we have a commit A and we create a commit B on top that changes our file. When we merge the pull request, we create a merge commit M. If no one else changed the file in the first-parent history between M and A, then M will not be TREESAME to its first parent, but will be TREESAME to B. Thus, the simplified history will be "B". However, M will appear in the --full-history mode.
However, suppose that a number of topics T1, T2, ..., Tn were created based on commits C1, C2, ..., Cn between A and M as follows:
A----C1----C2--- ... ---Cn----M------P1---P2--- ... ---Pn
\ \ \ \ / / / /
\ \__.. \ \/ ..__T1 / Tn
\ \__.. /\ ..__T2 /
\_____________________B \____________________/If the commits T1, T2, ... Tn did not change the file, then all of P1 through Pn will be TREESAME to their first parent, but not TREESAME to their second. This means that all of those merge commits appear in the --full-history view, with edges that immediately collapse into the lower history without introducing interesting single-parent commits.
The --simplify-merges option was introduced to remove these extra merge commits. By noticing that the rewritten parents are reachable from their first parents, those edges can be simplified away. Finally, the commits now look like single-parent commits that are TREESAME to their "only" parent. Thus, they are removed and this issue does not cause issues anymore. However, this also ends up removing the commit M from the history view! Even worse, the --simplify-merges option requires walking the entire history before returning a single result.
Many Git users are using Git alongside a Git service that provides code storage alongside a code review tool commonly called "Pull Requests" or "Merge Requests" against a target branch. When these requests are accepted and merged, they typically create a merge commit whose first parent is the previous branch tip and the second parent is the tip of the topic branch used for the request. This presents a valuable order to the parents, but also makes that merge commit slightly special. Users may want to see not only which commits changed a file, but which pull requests merged those commits into their branch. In the previous example, this would mean the users want to see the merge commit "M" in addition to the single- parent commit "C".
Users are even more likely to want these merge commits when they use pull requests to merge into a feature branch before merging that feature branch into their trunk.
In some sense, users are asking for the "first" merge commit to bring in the change to their branch. As long as the parent order is consistent, this can be handled with the following rule:
Include a merge commit if it is not TREESAME to its first parent, but is TREESAME to a later parent.
I call such merge commits "diversions" because they divert the history walk away from the first-parent history. As such, this change adds the "--include-diversions" option to rev-list and log. To test these options, extend the standard test example to include a merge commit that is not TREESAME to its first parent. It is surprising that that option was not already in the example, as it is instructive.
In particular, this extension demonstrates a common issue with file history simplification. When a user resolves a merge conflict using "-Xours" or otherwise ignoring one side of the conflict, they create a TREESAME edge that probably should not be TREESAME. This leads users to become frustrated and complain that "my change disappeared!" In my experience, showing them history with --full-history and --simplify-merges quickly reveals the problematic merge. As mentioned, this option is expensive to compute. The --include-diversions option _might_ show the merge commit (usually titled "resolving conflicts") more quickly. Of course, this depends on the user having the correct parent order, which is backwards when using "git pull".
There are some special considerations when combining the --include-diversions option with --simplify-merges. This requires adding a new DIVERSION object flag to store the information from the initial TREESAME comparisons. This helps avoid dropping those commits in later filters. This is covered by a test, including how the parents can be simplified. Since "struct object" has already ruined its 32-bit alignment by using 33 bits across parsed, type, and flags member, let's not make it worse. DIVERSION is used in revision.c with the same value (1u<<15) as REACHABLE in commit-graph.c. The REACHABLE flag is only used when writing a commit-graph file, and a revision walk using --include-diversions does not happen in the same process. Care must be taken in the future to ensure this remains the case.
Update Documentation/rev-list-options.txt with significant details around this option. This requires updating the example in the History Simplification section to demonstrate some of the problems with TREESAME second parents.
---
Add a new history mode
This --include-diversions option could use a better name.
An experienced developer in the Windows OS Engineering Systems team pointed out how hard it is to find out when a change was "introduced" in the Windows OS repo. Due to their multi-leveled, long-lived branch organization, a commit could be part of hundreds of pull requests as the branches are merged across the organization.
My default answer was "this is complicated not because of Git, but because of how you are branching." I then tried to explain how finding the "first merge" to include a commit is incredibly difficult and requires performing multiple reachability queries. As I was working it out on paper, I realized that was true if we relied only on the commit-graph shape to inform our qurey.
If we use the TREESAME information, then suddenly we get a much clearer picture! Let's simply pick out those merge commits that "introduced a change" because they are TREESAME to a non-first-parent (and not TREESAME to the first parent).
My name of "diversions" could probably use some work, but I like the basic concept of this option.
I welcome any and all feedback. Thanks!
UPDATES in v2:
* The functionality is a bit more complicated to work with --simplify-merges.
* The documentation is significantly expanded with an example that highlights the shortcomings of the default history simplification.
* The documented example is used in the test script instead of simply extending the previous example.
-Stolee
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-599%2Fderrickstolee%2Fnew-history-mode-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-599/derrickstolee/new-history-mode-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/599
Range-diff vs v1:
1: 8bf93688392 ! 1: 146c443e7f1 revision: --include-diversions adds helpful merges
@@ Commit message
more quickly. Of course, this depends on the user having the correct
parent order, which is backwards when using "git pull".
+ There are some special considerations when combining the
+ --include-diversions option with --simplify-merges. This requires
+ adding a new DIVERSION object flag to store the information from
+ the initial TREESAME comparisons. This helps avoid dropping those
+ commits in later filters. This is covered by a test, including how
+ the parents can be simplified. Since "struct object" has already
+ ruined its 32-bit alignment by using 33 bits across parsed, type,
+ and flags member, let's not make it worse. DIVERSION is used in
+ revision.c with the same value (1u<<15) as REACHABLE in
+ commit-graph.c. The REACHABLE flag is only used when writing a
+ commit-graph file, and a revision walk using --include-diversions
+ does not happen in the same process. Care must be taken in the
+ future to ensure this remains the case.
+
+ Update Documentation/rev-list-options.txt with significant details
+ around this option. This requires updating the example in the
+ History Simplification section to demonstrate some of the problems
+ with TREESAME second parents.
+
Signed-off-by: Derrick Stolee <[email protected]>
## Documentation/rev-list-options.txt ##
@@ Documentation/rev-list-options.txt: Default mode::
--full-history::
Same as the default mode, but does not prune some history.
+@@ Documentation/rev-list-options.txt: Note the major differences in `N`, `P`, and `Q` over `--full-history`:
+ parent and is TREESAME.
+ --
+
+-Finally, there is a fifth simplification mode available:
++There is another simplification mode available:
+
+ --ancestry-path::
+ Limit the displayed commits to those directly on the ancestry
+@@ Documentation/rev-list-options.txt: option does. Applied to the 'D..M' range, it results in:
+ L--M
+ -----------------------------------------------------------------------
+
++Before discussing another option, `--include-diversions`, we need to
++create a new example history.
+++
++A common problem users face when looking at simplified history is that a
++commit they know changed a file somehow does not appear in the file's
++simplified history. Let's demonstrate a new example and show how options
++such as `--full-history` and `--simplify-merges` works in that case:
+++
++-----------------------------------------------------------------------
++ .-A---M-----C--N---O---P
++ / / \ \ \/ / /
++ I B \ R-'`-Z' /
++ \ / \/ /
++ \ / /\ /
++ `---X--' `---Y--'
++-----------------------------------------------------------------------
+++
++For this example, suppose `I` created `file.txt` which was modified by
++`A`, `B`, and `X` in different ways. The single-parent commits `C`, `Z`,
++and `Y` do not change `file.txt`. The merge commit `M` was created by
++resolving the merge conflict to include both changes from `A` and `B`
++and hence is not TREESAME to either. The merge commit `R`, however, was
++created by ignoring the contents of `file.txt` at `M` and taking only
++the contents of `file.txt` at `X`. Hence, `R` is TREESAME to `X` but not
++`M`. Finally, the natural merge resolution to create `N` is to take the
++contents of `file.txt` at `R`, so `N` is TREESAME to `R` but not `C`.
++The merge commits `O` and `P` are TREESAME to their first parents, but
++not to their second parents, `Z` and `Y` respectively.
+++
++When using the default mode, `N` and `R` both have a TREESAME parent, so
++those edges are walked and the others are ignored. The resulting history
++graph is:
+++
++-----------------------------------------------------------------------
++ I---X
++-----------------------------------------------------------------------
+++
++When using `--full-history`, Git walks every edge. This will discover
++the commits `A` and `B` and the merge `M`, but also will reveal the
++merge commits `O` and `P`. With parent rewriting, the resulting graph is:
+++
++-----------------------------------------------------------------------
++ .-A---M--------N---O---P
++ / / \ \ \/ / /
++ I B \ R-'`--' /
++ \ / \/ /
++ \ / /\ /
++ `---X--' `------'
++-----------------------------------------------------------------------
+++
++Here, the merge commits `O` and `P` contribute extra noise, as they did
++not actually contribute a change to `file.txt`. They only merged a topic
++that was based on an older version of `file.txt`. This is a common
++issue in repositories using a workflow where many contributors work in
++parallel and merge their topic branches along a single trunk: manu
++unrelated merges appear in the `--full-history` results.
+++
++When using the `--simplify-merges` option, the commits `O` and `P`
++disappear from the results. This is because the rewritten second parents
++of `O` and `P` are reachable from their first parents. Those edges are
++removed and then the commits look like single-parent commits that are
++TREESAME to their parent. This also happens to the commit `N`, resulting
++in a history view as follows:
+++
++-----------------------------------------------------------------------
++ .-A---M--.
++ / / \
++ I B R
++ \ / /
++ \ / /
++ `---X--'
++-----------------------------------------------------------------------
+++
++In this view, we see all of the important single-parent changes from
++`A`, `B`, and `X`. We also see the carefully-resolved merge `M` and the
++not-so-carefully-resolved merge `R`. This is usually enough information
++to determine why the commits `A` and `B` "disappeared" from history in
++the default view. However, there are a few issues with this approach.
+++
++The first issue is performance. Unlike any previous option, the
++`--simplify-merges` option requires walking the entire commit history
++before returning a single result. This can make the option difficult to
++use for very large repositories.
+++
++The second issue is one of auditing. When many contributors are working
++on the same repository, it is important which merge commits introduced
++a change into an important branch. The problematic merge `R` above is
++not likely to be the merge commit that was used to merge into an
++important branch. Instead, the merge `N` was used to merge `R` and `X`
++into the important branch. This commit may have information about why
++the change `X` came to override the changes from `A` and `B` in its
++commit message.
+++
++The `--include-diversions` option helps with both of these issues. A
++merge commit is considered a "diverter" if it is not TREESAME to its
++first parent but is TREESAME to a later parent. These merges "divert"
++the history walk to a second parent instead of continuing along the
++first-parent history as expected. When using `--include-diversions`
++on this example (and no other options) the resulting graph is:
+++
++-----------------------------------------------------------------------
++ I---X---R---N
++-----------------------------------------------------------------------
+++
++Here, the merge commits `R` and `N` are included because they diverted
++the walk away from their first-parent history. They are the reason the
++commits `A` and `B` do not appear in the history.
+++
++When `--include-diversions` is paired with `--simplify-merges`, the
++graph includes all of the necessary information:
+++
++-----------------------------------------------------------------------
++ .-A---M--. N
++ / / \ /
++ I B R
++ \ / /
++ \ / /
++ `---X--'
++-----------------------------------------------------------------------
+++
++Notice that since `M` is reachable from `R`, the edge from `N` to `M`
++was simplified away. However, `N` still appears in the history as an
++important commit because it would divert a simplified history walk.
++
+ The `--simplify-by-decoration` option allows you to view only the
+ big picture of the topology of the history, by omitting commits
+ that are not referenced by tags. Commits are marked as !TREESAME
+
+ ## object.h ##
+@@ object.h: struct object_array {
+
+ /*
+ * object flag allocation:
+- * revision.h: 0---------10 25----28
++ * revision.h: 0---------10 15 25----28
+ * fetch-pack.c: 01
+ * negotiator/default.c: 2--5
+ * walker.c: 0-2
## revision.c ##
@@ revision.c: static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
@@ revision.c: static void try_to_simplify_commit(struct rev_info *revs, struct com
return;
case REV_TREE_NEW:
+@@ revision.c: static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
+ relevant_change = 1;
+ else
+ irrelevant_change = 1;
++
++ if (!nth_parent)
++ commit->object.flags |= DIVERSION;
++
+ continue;
+ }
+ die("bad tree compare for commit %s", oid_to_hex(&commit->object.oid));
@@ revision.c: static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
} else if (!strcmp(arg, "--full-diff")) {
revs->diff = 1;
@@ revision.c: static int handle_revision_opt(struct rev_info *revs, int argc, cons
} else if (!strcmp(arg, "--full-history")) {
revs->simplify_history = 0;
} else if (!strcmp(arg, "--relative-date")) {
+@@ revision.c: static struct commit_list **simplify_one(struct rev_info *revs, struct commit *c
+ if (!cnt ||
+ (commit->object.flags & UNINTERESTING) ||
+ !(commit->object.flags & TREESAME) ||
+- (parent = one_relevant_parent(revs, commit->parents)) == NULL)
++ (parent = one_relevant_parent(revs, commit->parents)) == NULL ||
++ (revs->diversions && (commit->object.flags & DIVERSION)))
+ st->simplified = commit;
+ else {
+ pst = locate_simplify_state(revs, parent);
+@@ revision.c: enum commit_action get_commit_action(struct rev_info *revs, struct commit *commi
+ /* drop merges unless we want parenthood */
+ if (!want_ancestry(revs))
+ return commit_ignore;
++
++ if (revs->diversions && (commit->object.flags & DIVERSION))
++ return commit_show;
++
+ /*
+ * If we want ancestry, then need to keep any merges
+ * between relevant commits to tie together topology.
## revision.h ##
+@@
+ #define SYMMETRIC_LEFT (1u<<8)
+ #define PATCHSAME (1u<<9)
+ #define BOTTOM (1u<<10)
++
++/* WARNING: This is also used as REACHABLE in commit-graph.c. */
++#define DIVERSION (1u<<15)
+ /*
+ * Indicates object was reached by traversal. i.e. not given by user on
+ * command-line or stdin.
+@@
+ */
+ #define NOT_USER_GIVEN (1u<<25)
+ #define TRACK_LINEAR (1u<<26)
+-#define ALL_REV_FLAGS (((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR)
++#define ALL_REV_FLAGS (((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR | DIVERSION)
+
+ #define TOPO_WALK_EXPLORED (1u<<27)
+ #define TOPO_WALK_INDEGREE (1u<<28)
@@ revision.h: struct rev_info {
no_walk:2,
remove_empty_trees:1,
@@ t/t6012-rev-list-simplify.sh: test_expect_success '--full-diff is not affected b
'
+#
-+# Modify the test repo to add a merge whose first parent is not TREESAME
-+# but whose second parent is TREESAME
++# Create a new history to demonstrate the value of --include-diversions
++# with respect to the subtleties of simplified history, --full-history,
++# and --simplify-merges.
++#
++# .-A---M-----C--N---O---P
++# / / \ \ \/ / /
++# I B \ R-'`-Z' /
++# \ / \/ /
++# \ / /\ /
++# `---X--' `---Y--'
+#
-+# A--B----------G--H--I--K--L--N
-+# \ \ / / /
-+# \ \ / / /
-+# C------E---F J /
-+# \ \_/ /
-+# \ /
-+# M-----------------
-+test_expect_success 'expand graph' '
-+ git switch -c branchM C &&
-+ echo "new data" >file &&
++# This example is explained in Documentation/rev-list-options.txt
++
++test_expect_success 'rebuild repo' '
++ rm -rf .git * &&
++ git init &&
++ git switch -c main &&
++
++ echo base >file &&
+ git add file &&
-+ test_tick &&
-+ test_commit M &&
++ test_commit I &&
+
-+ git checkout master &&
-+ git merge -Xtheirs branchM -m "N" &&
-+ note N
++ echo A >file &&
++ git add file &&
++ test_commit A &&
++
++ git switch -c branchB I &&
++ echo B >file &&
++ git add file &&
++ test_commit B &&
++
++ git switch main &&
++ test_must_fail git merge -m "M" B &&
++ echo A >file &&
++ echo B >>file &&
++ git add file &&
++ git merge --continue &&
++ note M &&
++
++ echo C >other &&
++ git add other &&
++ test_commit C &&
++
++ git switch -c branchX I &&
++ echo X >file &&
++ git add file &&
++ test_commit X &&
++
++ git switch -c branchR M &&
++ git merge -m R -Xtheirs X &&
++ note R &&
++
++ git switch main &&
++ git merge -m N R &&
++ note N &&
++
++ git switch -c branchY M &&
++ echo Y >y &&
++ git add y &&
++ test_commit Y &&
++
++ git switch -c branchZ C &&
++ echo Z >z &&
++ git add z &&
++ test_commit Z &&
++
++ git switch main &&
++ git merge -m O Z &&
++ note O &&
++
++ git merge -m P Y &&
++ note P
+'
+
-+check_result 'M C A' -- file
-+check_result 'N M C A' --include-diversions -- file
-+
-+check_result 'N M L K J I H F E D C G B A' --full-history --topo-order
-+check_result 'N M L K I H G F E D C B J A' --full-history
-+check_result 'N M L K I H G F E D C B J A' --full-history --date-order
-+check_result 'N M L K I H G F E D B C J A' --full-history --author-date-order
-+check_result 'N M K I H E C B A' --full-history -- file
-+check_result 'N M K I H E C B A' --full-history --topo-order -- file
-+check_result 'N M K I H E C B A' --full-history --date-order -- file
-+check_result 'N M K I H E B C A' --full-history --author-date-order -- file
-+check_result 'N M I E C B A' --simplify-merges -- file
-+check_result 'N M I E C B A' --simplify-merges --topo-order -- file
-+check_result 'N M I E C B A' --simplify-merges --date-order -- file
-+check_result 'N M I E B C A' --simplify-merges --author-date-order -- file
-+check_result 'M C A' --topo-order -- file
-+check_result 'M C A' --date-order -- file
-+check_result 'M C A' --author-date-order -- file
-+check_result 'H' --first-parent -- another-file
-+check_result 'H' --first-parent --topo-order -- another-file
++check_result 'X I' -- file
++check_result 'N R X I' --include-diversions -- file
++
++check_result 'P O N R X M B A I' --full-history --topo-order -- file
++check_result 'N R X M B A I' --simplify-merges --topo-order --include-diversions -- file
++check_result 'R X M B A I' --simplify-merges --topo-order -- file
++check_result 'N M A I' --first-parent -- file
++check_result 'N M A I' --first-parent --include-diversions -- file
++
++# --ancestry-path implies --full-history
++check_result 'P O N R M' --topo-order \
++ --ancestry-path A..HEAD -- file
++check_result 'P O N R M' --topo-order \
++ --include-diversions \
++ --ancestry-path A..HEAD -- file
++check_result 'P O N R M' --topo-order \
++ --full-history \
++ --ancestry-path A..HEAD -- file
++check_result 'R M' --topo-order \
++ --simplify-merges \
++ --ancestry-path A..HEAD -- file
++check_result 'N R M' --topo-order \
++ --simplify-merges --include-diversions \
++ --ancestry-path A..HEAD -- file
++
++test_expect_success 'log --graph --simplify-merges --include-diversions' '
++ cat >expect <<-\EOF &&
++ * N
++ * R
++ |\
++ | * X
++ * | M
++ |\ \
++ | * | B
++ | |/
++ * / A
++ |/
++ * I
++ EOF
++ git log --graph --pretty="%s" \
++ --simplify-merges --include-diversions \
++ -- file >actual &&
++ test_cmp expect actual
++'
+
test_doneDocumentation/rev-list-options.txt | 132 ++++++++++++++++++++++++++++- object.h | 2 +- revision.c | 27 +++++- revision.h | 6 +- t/t6012-rev-list-simplify.sh | 120 ++++++++++++++++++++++++++ 5 files changed, 282 insertions(+), 5 deletions(-)
Documentation/rev-list-options.txt +131 -1
@@ -342,6 +342,12 @@ Default mode:: branches if the end result is the same (i.e. merging branches with the same content) +--include-diversions:: + Include all commits from the default mode, but also any merge + commits that are not TREESAME to the first parent but are + TREESAME to a later parent. This mode is helpful for showing + the merge commits that "first introduced" a change to a branch. + --full-history:: Same as the default mode, but does not prune some history.
@@ -534,7 +540,7 @@ Note the major differences in `N`, `P`, and `Q` over `--full-history`: parent and is TREESAME. -- -Finally, there is a fifth simplification mode available: +There is another simplification mode available: --ancestry-path:: Limit the displayed commits to those directly on the ancestry
@@ -573,6 +579,130 @@ option does. Applied to the 'D..M' range, it results in: L--M ----------------------------------------------------------------------- +Before discussing another option, `--include-diversions`, we need to +create a new example history. ++ +A common problem users face when looking at simplified history is that a +commit they know changed a file somehow does not appear in the file's +simplified history. Let's demonstrate a new example and show how options +such as `--full-history` and `--simplify-merges` works in that case: ++ +----------------------------------------------------------------------- + .-A---M-----C--N---O---P + / / \ \ \/ / / + I B \ R-'`-Z' / + \ / \/ / + \ / /\ / + `---X--' `---Y--' +----------------------------------------------------------------------- ++ +For this example, suppose `I` created `file.txt` which was modified by +`A`, `B`, and `X` in different ways. The single-parent commits `C`, `Z`, +and `Y` do not change `file.txt`. The merge commit `M` was created by +resolving the merge conflict to include both changes from `A` and `B` +and hence is not TREESAME to either. The merge commit `R`, however, was +created by ignoring the contents of `file.txt` at `M` and taking only +the contents of `file.txt` at `X`. Hence, `R` is TREESAME to `X` but not +`M`. Finally, the natural merge resolution to create `N` is to take the +contents of `file.txt` at `R`, so `N` is TREESAME to `R` but not `C`. +The merge commits `O` and `P` are TREESAME to their first parents, but +not to their second parents, `Z` and `Y` respectively. ++ +When using the default mode, `N` and `R` both have a TREESAME parent, so +those edges are walked and the others are ignored. The resulting history +graph is: ++ +----------------------------------------------------------------------- + I---X +----------------------------------------------------------------------- ++ +When using `--full-history`, Git walks every edge. This will discover +the commits `A` and `B` and the merge `M`, but also will reveal the +merge commits `O` and `P`. With parent rewriting, the resulting graph is: ++ +----------------------------------------------------------------------- + .-A---M--------N---O---P + / / \ \ \/ / / + I B \ R-'`--' / + \ / \/ / + \ / /\ / + `---X--' `------' +----------------------------------------------------------------------- ++ +Here, the merge commits `O` and `P` contribute extra noise, as they did +not actually contribute a change to `file.txt`. They only merged a topic +that was based on an older version of `file.txt`. This is a common +issue in repositories using a workflow where many contributors work in +parallel and merge their topic branches along a single trunk: manu +unrelated merges appear in the `--full-history` results. ++ +When using the `--simplify-merges` option, the commits `O` and `P` +disappear from the results. This is because the rewritten second parents +of `O` and `P` are reachable from their first parents. Those edges are +removed and then the commits look like single-parent commits that are +TREESAME to their parent. This also happens to the commit `N`, resulting +in a history view as follows: ++ +----------------------------------------------------------------------- + .-A---M--. + / / \ + I B R + \ / / + \ / / + `---X--' +----------------------------------------------------------------------- ++ +In this view, we see all of the important single-parent changes from +`A`, `B`, and `X`. We also see the carefully-resolved merge `M` and the +not-so-carefully-resolved merge `R`. This is usually enough information +to determine why the commits `A` and `B` "disappeared" from history in +the default view. However, there are a few issues with this approach. ++ +The first issue is performance. Unlike any previous option, the +`--simplify-merges` option requires walking the entire commit history +before returning a single result. This can make the option difficult to +use for very large repositories. ++ +The second issue is one of auditing. When many contributors are working +on the same repository, it is important which merge commits introduced +a change into an important branch. The problematic merge `R` above is +not likely to be the merge commit that was used to merge into an +important branch. Instead, the merge `N` was used to merge `R` and `X` +into the important branch. This commit may have information about why +the change `X` came to override the changes from `A` and `B` in its +commit message. ++ +The `--include-diversions` option helps with both of these issues. A +merge commit is considered a "diverter" if it is not TREESAME to its +first parent but is TREESAME to a later parent. These merges "divert" +the history walk to a second parent instead of continuing along the +first-parent history as expected. When using `--include-diversions` +on this example (and no other options) the resulting graph is: ++ +----------------------------------------------------------------------- + I---X---R---N +----------------------------------------------------------------------- ++ +Here, the merge commits `R` and `N` are included because they diverted +the walk away from their first-parent history. They are the reason the +commits `A` and `B` do not appear in the history. ++ +When `--include-diversions` is paired with `--simplify-merges`, the +graph includes all of the necessary information: ++ +----------------------------------------------------------------------- + .-A---M--. N + / / \ / + I B R + \ / / + \ / / + `---X--' +----------------------------------------------------------------------- ++ +Notice that since `M` is reachable from `R`, the edge from `N` to `M` +was simplified away. However, `N` still appears in the history as an +important commit because it would divert a simplified history walk. + The `--simplify-by-decoration` option allows you to view only the big picture of the topology of the history, by omitting commits that are not referenced by tags. Commits are marked as !TREESAME
object.h +1 -1
@@ -59,7 +59,7 @@ struct object_array {/* * object flag allocation: -* revision.h: 0---------10 25----28 +* revision.h: 0---------10 15 25----28 * fetch-pack.c: 01 * negotiator/default.c: 2--5 * walker.c: 0-2
revision.c +25 -2
@@ -870,7 +870,19 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) } parent->next =NULL ; commit->parents = parent; - commit->object.flags |=TREESAME ; + +/* +* A merge commit is a "diversion" if it is not +* TREESAME to its first parent but is TREESAME +* to a later parent. In the simplified history, +* we "divert" the history walk to the later +* parent. These commits are shown when "diversions" +* is enabled, so do not mark the object as +* TREESAME here. +*/ +if (!revs->diversions || !nth_parent) + commit->object.flags |=TREESAME ; +return ;case REV_TREE_NEW :
@@ -897,6 +909,10 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) relevant_change =1 ; else irrelevant_change =1 ; + +if (!nth_parent) + commit->object.flags |=DIVERSION ; +continue ; }die ("bad tree compare for commit %s" ,oid_to_hex (&commit->object.oid));
@@ -2265,6 +2281,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg }else if (!strcmp (arg,"--full-diff" )) { revs->diff =1 ; revs->full_diff =1 ; + }else if (!strcmp (arg,"--include-diversions" )) { + revs->diversions =1 ; }else if (!strcmp (arg,"--full-history" )) { revs->simplify_history =0 ; }else if (!strcmp (arg,"--relative-date" )) {
@@ -3019,7 +3037,8 @@ static struct commit_list **simplify_one(struct rev_info *revs, struct commit *cif (!cnt || (commit->object.flags &UNINTERESTING ) || !(commit->object.flags &TREESAME ) || - (parent =one_relevant_parent (revs, commit->parents)) ==NULL ) + (parent =one_relevant_parent (revs, commit->parents)) ==NULL || + (revs->diversions && (commit->object.flags &DIVERSION ))) st->simplified = commit;else { pst =locate_simplify_state (revs, parent);
@@ -3602,6 +3621,10 @@ enum commit_action get_commit_action(struct rev_info *revs, struct commit *commi/* drop merges unless we want parenthood */ if (!want_ancestry (revs))return commit_ignore; + +if (revs->diversions && (commit->object.flags &DIVERSION )) +return commit_show; +/* * If we want ancestry, then need to keep any merges * between relevant commits to tie together topology.
revision.h +5 -1
@@ -34,6 +34,9 @@#define SYMMETRIC_LEFT (1u<<8)#define PATCHSAME (1u<<9)#define BOTTOM (1u<<10) + +/* WARNING: This is also used as REACHABLE in commit-graph.c. */ +#define DIVERSION (1u<<15)/* * Indicates object was reached by traversal. i.e. not given by user on * command-line or stdin.
@@ -43,7 +46,7 @@*/ #define NOT_USER_GIVEN (1u<<25)#define TRACK_LINEAR (1u<<26) -#define ALL_REV_FLAGS (((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR) +#define ALL_REV_FLAGS (((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR | DIVERSION)#define TOPO_WALK_EXPLORED (1u<<27)#define TOPO_WALK_INDEGREE (1u<<28)
@@ -129,6 +132,7 @@ struct rev_info { no_walk:2, remove_empty_trees:1, simplify_history:1, + diversions:1, topo_order:1, simplify_merges:1, simplify_by_decoration:1,
t/t6012-rev-list-simplify.sh +120 -0
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gitgitgadget
PATCH v3 1/1 revision: --show-pulls adds helpful merges
From: Derrick Stolee <[email protected]>
The default file history simplification of "git log -- <path>" or "git rev-list -- <path>" focuses on providing the smallest set of commits that first contributed a change. The revision walk greatly restricts the set of walked commits by visiting only the first TREESAME parent of a merge commit, when one exists. This means that portions of the commit-graph are not walked, which can be a performance benefit, but can also "hide" commits that added changes but were ignored by a merge resolution.
The --full-history option modifies this by walking all commits and reporting a merge commit as "interesting" if it has _any_ parent that is not TREESAME. This tends to be an over-representation of important commits, especially in an environment where most merge commits are created by pull request completion.
Suppose we have a commit A and we create a commit B on top that changes our file. When we merge the pull request, we create a merge commit M. If no one else changed the file in the first-parent history between M and A, then M will not be TREESAME to its first parent, but will be TREESAME to B. Thus, the simplified history will be "B". However, M will appear in the --full-history mode.
However, suppose that a number of topics T1, T2, ..., Tn were created based on commits C1, C2, ..., Cn between A and M as follows:
A----C1----C2--- ... ---Cn----M------P1---P2--- ... ---Pn
\ \ \ \ / / / /
\ \__.. \ \/ ..__T1 / Tn
\ \__.. /\ ..__T2 /
\_____________________B \____________________/If the commits T1, T2, ... Tn did not change the file, then all of P1 through Pn will be TREESAME to their first parent, but not TREESAME to their second. This means that all of those merge commits appear in the --full-history view, with edges that immediately collapse into the lower history without introducing interesting single-parent commits.
The --simplify-merges option was introduced to remove these extra merge commits. By noticing that the rewritten parents are reachable from their first parents, those edges can be simplified away. Finally, the commits now look like single-parent commits that are TREESAME to their "only" parent. Thus, they are removed and this issue does not cause issues anymore. However, this also ends up removing the commit M from the history view! Even worse, the --simplify-merges option requires walking the entire history before returning a single result.
Many Git users are using Git alongside a Git service that provides code storage alongside a code review tool commonly called "Pull Requests" or "Merge Requests" against a target branch. When these requests are accepted and merged, they typically create a merge commit whose first parent is the previous branch tip and the second parent is the tip of the topic branch used for the request. This presents a valuable order to the parents, but also makes that merge commit slightly special. Users may want to see not only which commits changed a file, but which pull requests merged those commits into their branch. In the previous example, this would mean the users want to see the merge commit "M" in addition to the single- parent commit "C".
Users are even more likely to want these merge commits when they use pull requests to merge into a feature branch before merging that feature branch into their trunk.
In some sense, users are asking for the "first" merge commit to bring in the change to their branch. As long as the parent order is consistent, this can be handled with the following rule:
Include a merge commit if it is not TREESAME to its first parent, but is TREESAME to a later parent.
These merges look like the merge commits that would result from running "git pull <topic>" on a main branch. Thus, the option to show these commits is called "--show-pulls". This has the added benefit of showing the commits created by closing a pull request or merge request on any of the Git hosting and code review platforms.
To test these options, extend the standard test example to include a merge commit that is not TREESAME to its first parent. It is surprising that that option was not already in the example, as it is instructive.
In particular, this extension demonstrates a common issue with file history simplification. When a user resolves a merge conflict using "-Xours" or otherwise ignoring one side of the conflict, they create a TREESAME edge that probably should not be TREESAME. This leads users to become frustrated and complain that "my change disappeared!" In my experience, showing them history with --full-history and --simplify-merges quickly reveals the problematic merge. As mentioned, this option is expensive to compute. The --show-pulls option _might_ show the merge commit (usually titled "resolving conflicts") more quickly. Of course, this depends on the user having the correct parent order, which is backwards when using "git pull master" from a topic branch.
There are some special considerations when combining the --show-pulls option with --simplify-merges. This requires adding a new PULL_MERGE object flag to store the information from the initial TREESAME comparisons. This helps avoid dropping those commits in later filters. This is covered by a test, including how the parents can be simplified. Since "struct object" has already ruined its 32-bit alignment by using 33 bits across parsed, type, and flags member, let's not make it worse. PULL_MERGE is used in revision.c with the same value (1u<<15) as REACHABLE in commit-graph.c. The REACHABLE flag is only used when writing a commit-graph file, and a revision walk using --show-pulls does not happen in the same process. Care must be taken in the future to ensure this remains the case.
Update Documentation/rev-list-options.txt with significant details around this option. This requires updating the example in the History Simplification section to demonstrate some of the problems with TREESAME second parents.
---
Add a new history mode
This --include-diversions option could use a better name.
An experienced developer in the Windows OS Engineering Systems team pointed out how hard it is to find out when a change was "introduced" in the Windows OS repo. Due to their multi-leveled, long-lived branch organization, a commit could be part of hundreds of pull requests as the branches are merged across the organization.
My default answer was "this is complicated not because of Git, but because of how you are branching." I then tried to explain how finding the "first merge" to include a commit is incredibly difficult and requires performing multiple reachability queries. As I was working it out on paper, I realized that was true if we relied only on the commit-graph shape to inform our qurey.
If we use the TREESAME information, then suddenly we get a much clearer picture! Let's simply pick out those merge commits that "introduced a change" because they are TREESAME to a non-first-parent (and not TREESAME to the first parent).
My name of "diversions" could probably use some work, but I like the basic concept of this option.
I welcome any and all feedback. Thanks!
UPDATES in v2:
* The functionality is a bit more complicated to work with --simplify-merges.
* The documentation is significantly expanded with an example that highlights the shortcomings of the default history simplification.
* The documented example is used in the test script instead of simply extending the previous example.
UPDATES in v3:
* Renamed things appropriately for the shift from "--include-diversions" to "--show-pulls".
* Slight rewording in the documentation to remove references to "diverters".
I don't recommend looking at the range-diff for this version.
-Stolee
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-599%2Fderrickstolee%2Fnew-history-mode-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-599/derrickstolee/new-history-mode-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/599
Range-diff vs v2:
1: 146c443e7f1 ! 1: 19026f4d4c0 revision: --include-diversions adds helpful merges
@@ Metadata
Author: Derrick Stolee <[email protected]>
## Commit message ##
- revision: --include-diversions adds helpful merges
+ revision: --show-pulls adds helpful merges
The default file history simplification of "git log -- <path>" or "git rev-list -- <path>" focuses on providing the smallest set of
@@ Commit message
Include a merge commit if it is not TREESAME to its first parent, but is TREESAME to a later parent.
- I call such merge commits "diversions" because they divert the
- history walk away from the first-parent history. As such, this
- change adds the "--include-diversions" option to rev-list and log.
+ These merges look like the merge commits that would result from
+ running "git pull <topic>" on a main branch. Thus, the option to
+ show these commits is called "--show-pulls". This has the added
+ benefit of showing the commits created by closing a pull request or
+ merge request on any of the Git hosting and code review platforms.
+
To test these options, extend the standard test example to include a merge commit that is not TREESAME to its first parent. It is surprising that that option was not already in the example, as it
@@ Commit message
users to become frustrated and complain that "my change disappeared!" In my experience, showing them history with --full-history and --simplify-merges quickly reveals the problematic merge. As mentioned,
- this option is expensive to compute. The --include-diversions option
+ this option is expensive to compute. The --show-pulls option
_might_ show the merge commit (usually titled "resolving conflicts") more quickly. Of course, this depends on the user having the correct
- parent order, which is backwards when using "git pull".
+ parent order, which is backwards when using "git pull master" from a
+ topic branch.
- There are some special considerations when combining the
- --include-diversions option with --simplify-merges. This requires
- adding a new DIVERSION object flag to store the information from
- the initial TREESAME comparisons. This helps avoid dropping those
- commits in later filters. This is covered by a test, including how
- the parents can be simplified. Since "struct object" has already
- ruined its 32-bit alignment by using 33 bits across parsed, type,
- and flags member, let's not make it worse. DIVERSION is used in
- revision.c with the same value (1u<<15) as REACHABLE in
- commit-graph.c. The REACHABLE flag is only used when writing a
- commit-graph file, and a revision walk using --include-diversions
- does not happen in the same process. Care must be taken in the
- future to ensure this remains the case.
+ There are some special considerations when combining the --show-pulls
+ option with --simplify-merges. This requires adding a new PULL_MERGE
+ object flag to store the information from the initial TREESAME
+ comparisons. This helps avoid dropping those commits in later filters.
+ This is covered by a test, including how the parents can be simplified.
+ Since "struct object" has already ruined its 32-bit alignment by using
+ 33 bits across parsed, type, and flags member, let's not make it worse.
+ PULL_MERGE is used in revision.c with the same value (1u<<15) as
+ REACHABLE in commit-graph.c. The REACHABLE flag is only used when
+ writing a commit-graph file, and a revision walk using --show-pulls
+ does not happen in the same process. Care must be taken in the future
+ to ensure this remains the case.
Update Documentation/rev-list-options.txt with significant details around this option. This requires updating the example in the
@@ Documentation/rev-list-options.txt: Default mode::
branches if the end result is the same (i.e. merging branches with the same content)
-+--include-diversions::
++--show-pulls::
+ Include all commits from the default mode, but also any merge
+ commits that are not TREESAME to the first parent but are
+ TREESAME to a later parent. This mode is helpful for showing
@@ Documentation/rev-list-options.txt: option does. Applied to the 'D..M' range, it
L--M
-----------------------------------------------------------------------
-+Before discussing another option, --include-diversions, we need to ++Before discussing another option, --show-pulls, we need to
+create a new example history.
++
+A common problem users face when looking at simplified history is that a
@@ Documentation/rev-list-options.txt: option does. Applied to the 'D..M' range, it
+the change X came to override the changes from A and B in its +commit message.
++
-+The --include-diversions option helps with both of these issues. A -+merge commit is considered a "diverter" if it is not TREESAME to its -+first parent but is TREESAME to a later parent. These merges "divert" -+the history walk to a second parent instead of continuing along the -+first-parent history as expected. When using --include-diversions -+on this example (and no other options) the resulting graph is:
++The --show-pulls option helps with both of these issues by adding more ++merge commits to the history results. If a merge is not TREESAME to its ++first parent but is TREESAME to a later parent, then that merge is ++treated as if it "pulled" the change from another branch. When using ++--show-pulls on this example (and no other options) the resulting ++graph is:
++
+-----------------------------------------------------------------------
+ I---X---R---N
+-----------------------------------------------------------------------
++
-+Here, the merge commits R and N are included because they diverted -+the walk away from their first-parent history. They are the reason the -+commits A and B do not appear in the history.
++Here, the merge commits R and N are included because they pulled ++the commits X and R into the base branch, respectively. These ++merges are the reason the commits A and B do not appear in the ++default history.
++
-+When --include-diversions is paired with --simplify-merges, the ++When --show-pulls is paired with --simplify-merges, the
+graph includes all of the necessary information:
++
+-----------------------------------------------------------------------
@@ Documentation/rev-list-options.txt: option does. Applied to the 'D..M' range, it
++
+Notice that since M is reachable from R, the edge from N to M +was simplified away. However, N still appears in the history as an
-+important commit because it would divert a simplified history walk. ++important commit because it "pulled" the change R into the main ++branch.
+
The --simplify-by-decoration option allows you to view only the big picture of the topology of the history, by omitting commits
@@ revision.c: static void try_to_simplify_commit(struct rev_info *revs, struct com
+ * TREESAME to its first parent but is TREESAME
+ * to a later parent. In the simplified history,
+ * we "divert" the history walk to the later
-+ * parent. These commits are shown when "diversions"
++ * parent. These commits are shown when "show_pulls"
+ * is enabled, so do not mark the object as
+ * TREESAME here.
+ */
-+ if (!revs->diversions || !nth_parent)
++ if (!revs->show_pulls || !nth_parent)
+ commit->object.flags |= TREESAME;
+
return;
@@ revision.c: static void try_to_simplify_commit(struct rev_info *revs, struct com
irrelevant_change = 1;
+
+ if (!nth_parent)
-+ commit->object.flags |= DIVERSION;
++ commit->object.flags |= PULL_MERGE;
+
continue;
}
@@ revision.c: static int handle_revision_opt(struct rev_info *revs, int argc, cons
} else if (!strcmp(arg, "--full-diff")) {
revs->diff = 1;
revs->full_diff = 1;
-+ } else if (!strcmp(arg, "--include-diversions")) {
-+ revs->diversions = 1;
++ } else if (!strcmp(arg, "--show-pulls")) {
++ revs->show_pulls = 1;
} else if (!strcmp(arg, "--full-history")) {
revs->simplify_history = 0;
} else if (!strcmp(arg, "--relative-date")) {
@@ revision.c: static struct commit_list **simplify_one(struct rev_info *revs, stru
!(commit->object.flags & TREESAME) ||
- (parent = one_relevant_parent(revs, commit->parents)) == NULL)
+ (parent = one_relevant_parent(revs, commit->parents)) == NULL ||
-+ (revs->diversions && (commit->object.flags & DIVERSION)))
++ (revs->show_pulls && (commit->object.flags & PULL_MERGE)))
st->simplified = commit;
else {
pst = locate_simplify_state(revs, parent);
@@ revision.c: enum commit_action get_commit_action(struct rev_info *revs, struct c
if (!want_ancestry(revs))
return commit_ignore;
+
-+ if (revs->diversions && (commit->object.flags & DIVERSION))
++ if (revs->show_pulls && (commit->object.flags & PULL_MERGE))
+ return commit_show;
+
/*
@@ revision.h
#define BOTTOM (1u<<10)
+
+/* WARNING: This is also used as REACHABLE in commit-graph.c. */
-+#define DIVERSION (1u<<15)
++#define PULL_MERGE (1u<<15)
/*
* Indicates object was reached by traversal. i.e. not given by user on
* command-line or stdin.
@@ revision.h
#define NOT_USER_GIVEN (1u<<25)
#define TRACK_LINEAR (1u<<26)
-#define ALL_REV_FLAGS (((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR)
-+#define ALL_REV_FLAGS (((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR | DIVERSION)
++#define ALL_REV_FLAGS (((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR | PULL_MERGE)
#define TOPO_WALK_EXPLORED (1u<<27)
#define TOPO_WALK_INDEGREE (1u<<28)
@@ revision.h: struct rev_info {
no_walk:2,
remove_empty_trees:1,
simplify_history:1,
-+ diversions:1,
++ show_pulls:1,
topo_order:1,
simplify_merges:1,
simplify_by_decoration:1,
@@ t/t6012-rev-list-simplify.sh: test_expect_success '--full-diff is not affected b
'
+#
-+# Create a new history to demonstrate the value of --include-diversions ++# Create a new history to demonstrate the value of --show-pulls
+# with respect to the subtleties of simplified history, --full-history, +# and --simplify-merges.
+#
@@ t/t6012-rev-list-simplify.sh: test_expect_success '--full-diff is not affected b
+'
+
+check_result 'X I' -- file
-+check_result 'N R X I' --include-diversions -- file
++check_result 'N R X I' --show-pulls -- file
+
+check_result 'P O N R X M B A I' --full-history --topo-order -- file
-+check_result 'N R X M B A I' --simplify-merges --topo-order --include-diversions -- file ++check_result 'N R X M B A I' --simplify-merges --topo-order --show-pulls -- file
+check_result 'R X M B A I' --simplify-merges --topo-order -- file +check_result 'N M A I' --first-parent -- file
-+check_result 'N M A I' --first-parent --include-diversions -- file ++check_result 'N M A I' --first-parent --show-pulls -- file
+
+# --ancestry-path implies --full-history
+check_result 'P O N R M' --topo-order \
+ --ancestry-path A..HEAD -- file
+check_result 'P O N R M' --topo-order \
-+ --include-diversions \
++ --show-pulls \
+ --ancestry-path A..HEAD -- file
+check_result 'P O N R M' --topo-order \
+ --full-history \
@@ t/t6012-rev-list-simplify.sh: test_expect_success '--full-diff is not affected b
+ --simplify-merges \
+ --ancestry-path A..HEAD -- file
+check_result 'N R M' --topo-order \
-+ --simplify-merges --include-diversions \
++ --simplify-merges --show-pulls \
+ --ancestry-path A..HEAD -- file
+
-+test_expect_success 'log --graph --simplify-merges --include-diversions' ' ++test_expect_success 'log --graph --simplify-merges --show-pulls' '
+ cat >expect <<-\EOF &&
+ * N
+ * R
@@ t/t6012-rev-list-simplify.sh: test_expect_success '--full-diff is not affected b
+ * I
+ EOF
+ git log --graph --pretty="%s" \
-+ --simplify-merges --include-diversions \
++ --simplify-merges --show-pulls \
+ -- file >actual &&
+ test_cmp expect actual
+'
Documentation/rev-list-options.txt | 134 ++++++++++++++++++++++++++++- object.h | 2 +- revision.c | 27 +++++- revision.h | 6 +- t/t6012-rev-list-simplify.sh | 120 ++++++++++++++++++++++++++ 5 files changed, 284 insertions(+), 5 deletions(-)
Documentation/rev-list-options.txt +133 -1
@@ -342,6 +342,12 @@ Default mode:: branches if the end result is the same (i.e. merging branches with the same content) +--show-pulls:: + Include all commits from the default mode, but also any merge + commits that are not TREESAME to the first parent but are + TREESAME to a later parent. This mode is helpful for showing + the merge commits that "first introduced" a change to a branch. + --full-history:: Same as the default mode, but does not prune some history.
@@ -534,7 +540,7 @@ Note the major differences in `N`, `P`, and `Q` over `--full-history`: parent and is TREESAME. -- -Finally, there is a fifth simplification mode available: +There is another simplification mode available: --ancestry-path:: Limit the displayed commits to those directly on the ancestry
@@ -573,6 +579,132 @@ option does. Applied to the 'D..M' range, it results in: L--M ----------------------------------------------------------------------- +Before discussing another option, `--show-pulls`, we need to +create a new example history. ++ +A common problem users face when looking at simplified history is that a +commit they know changed a file somehow does not appear in the file's +simplified history. Let's demonstrate a new example and show how options +such as `--full-history` and `--simplify-merges` works in that case: ++ +----------------------------------------------------------------------- + .-A---M-----C--N---O---P + / / \ \ \/ / / + I B \ R-'`-Z' / + \ / \/ / + \ / /\ / + `---X--' `---Y--' +----------------------------------------------------------------------- ++ +For this example, suppose `I` created `file.txt` which was modified by +`A`, `B`, and `X` in different ways. The single-parent commits `C`, `Z`, +and `Y` do not change `file.txt`. The merge commit `M` was created by +resolving the merge conflict to include both changes from `A` and `B` +and hence is not TREESAME to either. The merge commit `R`, however, was +created by ignoring the contents of `file.txt` at `M` and taking only +the contents of `file.txt` at `X`. Hence, `R` is TREESAME to `X` but not +`M`. Finally, the natural merge resolution to create `N` is to take the +contents of `file.txt` at `R`, so `N` is TREESAME to `R` but not `C`. +The merge commits `O` and `P` are TREESAME to their first parents, but +not to their second parents, `Z` and `Y` respectively. ++ +When using the default mode, `N` and `R` both have a TREESAME parent, so +those edges are walked and the others are ignored. The resulting history +graph is: ++ +----------------------------------------------------------------------- + I---X +----------------------------------------------------------------------- ++ +When using `--full-history`, Git walks every edge. This will discover +the commits `A` and `B` and the merge `M`, but also will reveal the +merge commits `O` and `P`. With parent rewriting, the resulting graph is: ++ +----------------------------------------------------------------------- + .-A---M--------N---O---P + / / \ \ \/ / / + I B \ R-'`--' / + \ / \/ / + \ / /\ / + `---X--' `------' +----------------------------------------------------------------------- ++ +Here, the merge commits `O` and `P` contribute extra noise, as they did +not actually contribute a change to `file.txt`. They only merged a topic +that was based on an older version of `file.txt`. This is a common +issue in repositories using a workflow where many contributors work in +parallel and merge their topic branches along a single trunk: manu +unrelated merges appear in the `--full-history` results. ++ +When using the `--simplify-merges` option, the commits `O` and `P` +disappear from the results. This is because the rewritten second parents +of `O` and `P` are reachable from their first parents. Those edges are +removed and then the commits look like single-parent commits that are +TREESAME to their parent. This also happens to the commit `N`, resulting +in a history view as follows: ++ +----------------------------------------------------------------------- + .-A---M--. + / / \ + I B R + \ / / + \ / / + `---X--' +----------------------------------------------------------------------- ++ +In this view, we see all of the important single-parent changes from +`A`, `B`, and `X`. We also see the carefully-resolved merge `M` and the +not-so-carefully-resolved merge `R`. This is usually enough information +to determine why the commits `A` and `B` "disappeared" from history in +the default view. However, there are a few issues with this approach. ++ +The first issue is performance. Unlike any previous option, the +`--simplify-merges` option requires walking the entire commit history +before returning a single result. This can make the option difficult to +use for very large repositories. ++ +The second issue is one of auditing. When many contributors are working +on the same repository, it is important which merge commits introduced +a change into an important branch. The problematic merge `R` above is +not likely to be the merge commit that was used to merge into an +important branch. Instead, the merge `N` was used to merge `R` and `X` +into the important branch. This commit may have information about why +the change `X` came to override the changes from `A` and `B` in its +commit message. ++ +The `--show-pulls` option helps with both of these issues by adding more +merge commits to the history results. If a merge is not TREESAME to its +first parent but is TREESAME to a later parent, then that merge is +treated as if it "pulled" the change from another branch. When using +`--show-pulls` on this example (and no other options) the resulting +graph is: ++ +----------------------------------------------------------------------- + I---X---R---N +----------------------------------------------------------------------- ++ +Here, the merge commits `R` and `N` are included because they pulled +the commits `X` and `R` into the base branch, respectively. These +merges are the reason the commits `A` and `B` do not appear in the +default history. ++ +When `--show-pulls` is paired with `--simplify-merges`, the +graph includes all of the necessary information: ++ +----------------------------------------------------------------------- + .-A---M--. N + / / \ / + I B R + \ / / + \ / / + `---X--' +----------------------------------------------------------------------- ++ +Notice that since `M` is reachable from `R`, the edge from `N` to `M` +was simplified away. However, `N` still appears in the history as an +important commit because it "pulled" the change `R` into the main +branch. + The `--simplify-by-decoration` option allows you to view only the big picture of the topology of the history, by omitting commits that are not referenced by tags. Commits are marked as !TREESAME
object.h +1 -1
@@ -59,7 +59,7 @@ struct object_array {/* * object flag allocation: -* revision.h: 0---------10 25----28 +* revision.h: 0---------10 15 25----28 * fetch-pack.c: 01 * negotiator/default.c: 2--5 * walker.c: 0-2
revision.c +25 -2
@@ -870,7 +870,19 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) } parent->next =NULL ; commit->parents = parent; - commit->object.flags |=TREESAME ; + +/* +* A merge commit is a "diversion" if it is not +* TREESAME to its first parent but is TREESAME +* to a later parent. In the simplified history, +* we "divert" the history walk to the later +* parent. These commits are shown when "show_pulls" +* is enabled, so do not mark the object as +* TREESAME here. +*/ +if (!revs->show_pulls || !nth_parent) + commit->object.flags |=TREESAME ; +return ;case REV_TREE_NEW :
@@ -897,6 +909,10 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) relevant_change =1 ; else irrelevant_change =1 ; + +if (!nth_parent) + commit->object.flags |=PULL_MERGE ; +continue ; }die ("bad tree compare for commit %s" ,oid_to_hex (&commit->object.oid));
@@ -2265,6 +2281,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg }else if (!strcmp (arg,"--full-diff" )) { revs->diff =1 ; revs->full_diff =1 ; + }else if (!strcmp (arg,"--show-pulls" )) { + revs->show_pulls =1 ; }else if (!strcmp (arg,"--full-history" )) { revs->simplify_history =0 ; }else if (!strcmp (arg,"--relative-date" )) {
@@ -3019,7 +3037,8 @@ static struct commit_list **simplify_one(struct rev_info *revs, struct commit *cif (!cnt || (commit->object.flags &UNINTERESTING ) || !(commit->object.flags &TREESAME ) || - (parent =one_relevant_parent (revs, commit->parents)) ==NULL ) + (parent =one_relevant_parent (revs, commit->parents)) ==NULL || + (revs->show_pulls && (commit->object.flags &PULL_MERGE ))) st->simplified = commit;else { pst =locate_simplify_state (revs, parent);
@@ -3602,6 +3621,10 @@ enum commit_action get_commit_action(struct rev_info *revs, struct commit *commi/* drop merges unless we want parenthood */ if (!want_ancestry (revs))return commit_ignore; + +if (revs->show_pulls && (commit->object.flags &PULL_MERGE )) +return commit_show; +/* * If we want ancestry, then need to keep any merges * between relevant commits to tie together topology.
revision.h +5 -1
@@ -34,6 +34,9 @@#define SYMMETRIC_LEFT (1u<<8)#define PATCHSAME (1u<<9)#define BOTTOM (1u<<10) + +/* WARNING: This is also used as REACHABLE in commit-graph.c. */ +#define PULL_MERGE (1u<<15)/* * Indicates object was reached by traversal. i.e. not given by user on * command-line or stdin.
@@ -43,7 +46,7 @@*/ #define NOT_USER_GIVEN (1u<<25)#define TRACK_LINEAR (1u<<26) -#define ALL_REV_FLAGS (((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR) +#define ALL_REV_FLAGS (((1u<<11)-1) | NOT_USER_GIVEN | TRACK_LINEAR | PULL_MERGE)#define TOPO_WALK_EXPLORED (1u<<27)#define TOPO_WALK_INDEGREE (1u<<28)
@@ -129,6 +132,7 @@ struct rev_info { no_walk:2, remove_empty_trees:1, simplify_history:1, + show_pulls:1, topo_order:1, simplify_merges:1, simplify_by_decoration:1,
t/t6012-rev-list-simplify.sh +120 -0
124 lines not on this page · raw message
base-commit: 274b9cc25322d9ee79aa8e6d4e86f0ffe5ced925
Signature · 1 line
gitgitgadget
Re: [PATCH v3] revision: --show-pulls adds helpful merges
Quoted 13 lines · Derrick Stolee via GitGitGadget
A----C1----C2--- ... ---Cn----M------P1---P2--- ... ---Pn
\ \ \ \ / / / /\ \__.. \ \/ ..__T1 / Tn \ \__.. /\ ..__T2 / \_____________________B \____________________/If the commits T1, T2, ... Tn did not change the file, then all of P1 through Pn will be TREESAME to their first parent, but not TREESAME to their second. This means that all of those merge commits appear in the --full-history view, with edges that immediately collapse into the lower history without introducing interesting single-parent commits.
Quoted 8 lines
The --simplify-merges option was introduced to remove these extra merge commits. By noticing that the rewritten parents are reachable from their first parents, those edges can be simplified away. Finally, the commits now look like single-parent commits that are TREESAME to their "only" parent. Thus, they are removed and this issue does not cause issues anymore. However, this also ends up removing the commit M from the history view! Even worse, the --simplify-merges option requires walking the entire history before returning a single result.
True. It is not advisable to use --simplify-merges unless you are limiting the history at the bottom for that reason.
Quoted 6 lines
In some sense, users are asking for the "first" merge commit to bring in the change to their branch. As long as the parent order is consistent, this can be handled with the following rule:
Include a merge commit if it is not TREESAME to its first parent, but is TREESAME to a later parent.
"but is" -> "even if it is" would make it a bit more accurate, I would think. Normally, such a merge that is treesame to some side branch is omitted from the output, but the rule wants it to be shown even if all the changes were brought in from one single parent.
Quoted 4 lines
Update
Documentation/rev-list-options.txtwith significant details around this option. This requires updating the example in the History Simplification section to demonstrate some of the problems with TREESAME second parents.
Good.
Quoted 8 lines
revision.c +0
-0@@ -870,7 +870,19 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) } parent->next =NULL ; commit->parents = parent;
revision.c static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) · line 881
Quoted 10 lines
revision.c +9
-1- commit->object.flags |=TREESAME ; + +/* +* A merge commit is a "diversion" if it is not +* TREESAME to its first parent but is TREESAME +* to a later parent. In the simplified history, +* we "divert" the history walk to the later +* parent. These commits are shown when "show_pulls" +* is enabled, so do not mark the object as +* TREESAME here.
As we no longer use the word "diversion", this explanation should shift the focus from defining the word "diversion" and giving its background to explaining why the above parent rewriting is done and why the TREESAME marking is conditional, e.g.
The tree of the merge and of the parent are the same; from here on, we stop following histories of all other parents but this one by culling commit->parents list. We also normally mark the merge commit TREESAME as the merge itself did not introduce any change relative to the parent, but we refrain from doing so for the first parent under "--show-pulls" mode, in order to let the output phase to show the merge, which is the last commit before we divert our walk to a side history.
or something along that line.
revision.c static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) · line 914
Quoted 12 lines
revision.c +6
-0+if (!revs->show_pulls || !nth_parent) + commit->object.flags |=TREESAME ; +return ;@@ -897,6 +909,10 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) relevant_change =1 ; else irrelevant_change =1 ; + +if (!nth_parent) + commit->object.flags |=PULL_MERGE ;
For a three-parent merge that brings in changes to the first parent, if the result matches the second parent, we would have returned in the previous hunk before having a chance to inspect the third one and marking the merge result with PULL_MERGE, but if you swap the order of the second and the third parent, the second parent, which has different tree from the result, would not return in the previous hunk and cause the merge with PULL_MERGE here. And then when we inspect the third parent, the previous hunk's return would kick in. So for two merges that merge exactly the same two branches on top of exactly the same commit on the mainline, you sometimes mark the result with PULL_MERGE and sometimes don't, depending on the order of the second and the third parent.
That feels iffy. Treating the first parent differently from others is what we intend to do with this change, bhut this hunk treats the other parents differently depending on the merge order.
revision.c static struct commit_list **simplify_one(struct rev_info *revs, struct commit *c · line 3042
Quoted 8 lines
revision.c +2
-1@@ -3019,7 +3037,8 @@ static struct commit_list **simplify_one(struct rev_info *revs, struct commit *cif (!cnt || (commit->object.flags &UNINTERESTING ) || !(commit->object.flags &TREESAME ) || - (parent =one_relevant_parent (revs, commit->parents)) ==NULL ) + (parent =one_relevant_parent (revs, commit->parents)) ==NULL || + (revs->show_pulls && (commit->object.flags &PULL_MERGE ))) st->simplified = commit;
... hence, wouldn't we see different result here ...
revision.c enum commit_action get_commit_action(struct rev_info *revs, struct commit *commi · line 3626
Quoted 7 lines
revision.c +3
-0@@ -3602,6 +3621,10 @@ enum commit_action get_commit_action(struct rev_info *revs, struct commit *commi/* drop merges unless we want parenthood */ if (!want_ancestry (revs))return commit_ignore; + +if (revs->show_pulls && (commit->object.flags &PULL_MERGE )) +return commit_show;
... and also here?
Thanks.
Re: [PATCH v3] revision: --show-pulls adds helpful merges
Quoted 24 lines · Junio C Hamano
Quoted 13 lines · Derrick Stolee via GitGitGadget
A----C1----C2--- ... ---Cn----M------P1---P2--- ... ---Pn
\ \ \ \ / / / /\ \__.. \ \/ ..__T1 / Tn \ \__.. /\ ..__T2 / \_____________________B \____________________/If the commits T1, T2, ... Tn did not change the file, then all of P1 through Pn will be TREESAME to their first parent, but not TREESAME to their second. This means that all of those merge commits appear in the --full-history view, with edges that immediately collapse into the lower history without introducing interesting single-parent commits.
Quoted 8 lines
The --simplify-merges option was introduced to remove these extra merge commits. By noticing that the rewritten parents are reachable from their first parents, those edges can be simplified away. Finally, the commits now look like single-parent commits that are TREESAME to their "only" parent. Thus, they are removed and this issue does not cause issues anymore. However, this also ends up removing the commit M from the history view! Even worse, the --simplify-merges option requires walking the entire history before returning a single result.
Quoted 2 lines
True. It is not advisable to use --simplify-merges unless you are limiting the history at the bottom for that reason.
I will modify my advice to include this "limiting the history at the bottom" advice.
Quoted 11 lines
Quoted 6 lines
In some sense, users are asking for the "first" merge commit to bring in the change to their branch. As long as the parent order is consistent, this can be handled with the following rule:
Include a merge commit if it is not TREESAME to its first parent, but is TREESAME to a later parent.
"but is" -> "even if it is" would make it a bit more accurate, I would think. Normally, such a merge that is treesame to some side branch is omitted from the output, but the rule wants it to be shown even if all the changes were brought in from one single parent.
This is an excellent clarification, since the way I wrote it does not describe every merge that we include. I wrote it to include the "extra" merges that are included. A better strategy is to include a complete description of every merge commit that appears in the output, as you defined it.
Quoted 22 lines
Quoted 4 lines
Update
Documentation/rev-list-options.txtwith significant details around this option. This requires updating the example in the History Simplification section to demonstrate some of the problems with TREESAME second parents.Good.
Quoted 15 lines
revision.c +6
-1@@ -870,7 +870,19 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) } parent->next =NULL ; commit->parents = parent; - commit->object.flags |=TREESAME ; + +/* +* A merge commit is a "diversion" if it is not +* TREESAME to its first parent but is TREESAME +* to a later parent. In the simplified history, +* we "divert" the history walk to the later
Quoted 8 lines
revision.c static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) · line 881
Quoted 3 lines
revision.c +3
-0+* parent. These commits are shown when "show_pulls" +* is enabled, so do not mark the object as +* TREESAME here. As we no longer use the word "diversion", this explanation should shift the focus from defining the word "diversion" and giving its background to explaining why the above parent rewriting is done and why the TREESAME marking is conditional, e.g.
Sorry about this. I intended to replace all references to this old terminology, but failed.
Quoted 13 lines
The tree of the merge and of the parent are the same; from here on, we stop following histories of all other parents but this one by culling
commit->parentslist. We also normally mark the merge commit TREESAME as the merge itself did not introduce any change relative to the parent, but we refrain from doing so for the first parent under "--show-pulls" mode, in order to let the output phase to show the merge, which is the last commit before we divert our walk to a side history.
Quoted 1 line
or something along that line.
This is pretty good. I plan to take it with very minor modifications in my next version.
Quoted 27 lines
revision.c static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) · line 914
Quoted 13 lines
revision.c +6
-0+if (!revs->show_pulls || !nth_parent) + commit->object.flags |=TREESAME ; +return ;@@ -897,6 +909,10 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit) relevant_change =1 ; else irrelevant_change =1 ; + +if (!nth_parent) + commit->object.flags |=PULL_MERGE ;For a three-parent merge that brings in changes to the first parent, if the result matches the second parent, we would have returned in the previous hunk before having a chance to inspect the third one and marking the merge result with
PULL_MERGE, but if you swap the order of the second and the third parent, the second parent, which has different tree from the result, would not return in the previous hunk and cause the merge withPULL_MERGEhere. And then when we inspect the third parent, the previous hunk's return would kick in. So for two merges that merge exactly the same two branches on top of exactly the same commit on the mainline, you sometimes mark the result withPULL_MERGEand sometimes don't, depending on the order of the second and the third parent.
Quoted 3 lines
That feels iffy. Treating the first parent differently from others is what we intend to do with this change, bhut this hunk treats the other parents differently depending on the merge order.
It is worth adding a test with an octopus merge to really be clear about the intended behavior. When describing the concept, I've been careful to say "TREESAME to the first parent" and "not TREESAME to a later parent" instead of assuming two parents. In the default mode, we should not reach here unless we found a TREESAME parent that was not the first parent, since we stop visiting parents after we find any TREESAME parent. But this would change for --full-history or --simplify-merges.
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revision.c static struct commit_list **simplify_one(struct rev_info *revs, struct commit *c · line 3042
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revision.c +2
-1@@ -3019,7 +3037,8 @@ static struct commit_list **simplify_one(struct rev_info *revs, struct commit *cif (!cnt || (commit->object.flags &UNINTERESTING ) || !(commit->object.flags &TREESAME ) || - (parent =one_relevant_parent (revs, commit->parents)) ==NULL ) + (parent =one_relevant_parent (revs, commit->parents)) ==NULL || + (revs->show_pulls && (commit->object.flags &PULL_MERGE ))) st->simplified = commit;... hence, wouldn't we see different result here ...
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revision.c enum commit_action get_commit_action(struct rev_info *revs, struct commit *commi · line 3626
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revision.c +3
-0@@ -3602,6 +3621,10 @@ enum commit_action get_commit_action(struct rev_info *revs, struct commit *commi/* drop merges unless we want parenthood */ if (!want_ancestry (revs))return commit_ignore; + +if (revs->show_pulls && (commit->object.flags &PULL_MERGE )) +return commit_show;... and also here?
If there is a flaw in how I set PULL_MERGE, then hopefully the fix is where I assign the PULL_MERGE flag and these lines do not need to change.
Thanks,
-Stolee