diff: implement config.diff.renames=copies-harder

From: Sam James <[email protected]>

This patch adds a config value for 'diff.renames' called 'copies-harder' which make it so '-C -C' is in effect always passed for 'git log -p', 'git diff', etc.

This allows specifying that 'git log -p', 'git diff', etc should always act as if '-C --find-copies-harder' was passed.

I've found this especially useful for certain types of repository (like Gentoo's ebuild repositories) because files are often copies of a previous version.

Signed-off-by Sam James <[email protected]>

---
diff: implement config.diff.renames=copies-harder

This patch adds a config value for 'diff.renames' called 'copies-harder' which make it so '-C -C' is in effect always passed for 'git log -p', 'git diff', etc.

This allows specifying that 'git log -p', 'git diff', etc should always act as if '-C --find-copies-harder' was passed.

I've found this especially useful for certain types of repository (like Gentoo's ebuild repositories) because files are often copies of a previous version.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1606%2Fthesamesam%2Fconfig-copies-harder-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1606/thesamesam/config-copies-harder-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1606

 Documentation/config/diff.txt   |  3 ++-
 Documentation/config/status.txt |  3 ++-
 diff.c                          | 12 +++++++++---
 diff.h                          |  1 +
 diffcore-rename.c               |  4 ++--
 merge-ort.c                     |  2 +-
 merge-recursive.c               |  2 +-
 7 files changed, 18 insertions(+), 9 deletions(-)

Documentation/config/diff.txt +0 -0

index bd5ae0c3378..d2ff3c62d41 100644

Documentation/config/diff.txt +0 -0

        affects only 'git diff' Porcelain like linkgit:git-diff[1] and
        linkgit:git-log[1], and not lower level commands such as
        linkgit:git-diff-files[1].

Documentation/config/status.txt +0 -0

index 2ff8237f8fc..7ca7a4becd7 100644

Documentation/config/status.txt +0 -0

        Defaults to the value of diff.renames.
 
 status.showStash::

diff.c +0 -0

index 2c602df10a3..0ca906611f5 100644

diff.c +0 -0

                options->flags.find_copies_harder = 1;
        else
                options->detect_rename = DIFF_DETECT_COPY;

diff.h +1 -0

index 66bd8aeb293..b29e5b777f8 100644
@@ -555,6 +555,7 @@ int git_config_rename(const char *var, const char *value);
 
 #define DIFF_DETECT_RENAME     1
 #define DIFF_DETECT_COPY       2
+#define DIFF_DETECT_COPY_HARDER 3
 
 #define DIFF_PICKAXE_ALL       1
 #define DIFF_PICKAXE_REGEX     2

diffcore-rename.c +0 -0

index 5a6e2bcac71..856291d66f2 100644

diffcore-rename.c +0 -0

        if (dirs_removed && (break_idx || want_copies))
                BUG("dirs_removed incompatible with break/copy detection");
        if (break_idx && relevant_sources)

merge-ort.c +1 -1

index 6491070d965..77498354652 100644
@@ -4782,7 +4782,7 @@ static void merge_start(struct merge_options *opt, struct merge_result *result)
         * sanity check them anyway.
         */
        assert(opt->detect_renames >= -1 &&
-              opt->detect_renames <= DIFF_DETECT_COPY);
+              opt->detect_renames <= DIFF_DETECT_COPY_HARDER);
        assert(opt->verbosity >= 0 && opt->verbosity <= 5);
        assert(opt->buffer_output <= 2);
        assert(opt->obuf.len == 0);

merge-recursive.c +1 -1

index e3beb0801b1..d52dd536606 100644
@@ -3708,7 +3708,7 @@ static int merge_start(struct merge_options *opt, struct tree *head)
        assert(opt->branch1 && opt->branch2);
 
        assert(opt->detect_renames >= -1 &&
-              opt->detect_renames <= DIFF_DETECT_COPY);
+              opt->detect_renames <= DIFF_DETECT_COPY_HARDER);
        assert(opt->detect_directory_renames >= MERGE_DIRECTORY_RENAMES_NONE &&
               opt->detect_directory_renames <= MERGE_DIRECTORY_RENAMES_TRUE);
        assert(opt->rename_limit >= -1);

base-commit: 692be87cbba55e8488f805d236f2ad50483bd7d5 --
gitgitgadget

Quoted 10 lines · Sam James via GitGitGadget

From: Sam James <[email protected]>

This patch adds a config value for 'diff.renames' called 'copies-harder' which make it so '-C -C' is in effect always passed for 'git log -p', 'git diff', etc.

This allows specifying that 'git log -p', 'git diff', etc should always act as if '-C --find-copies-harder' was passed.

Quoted 3 lines

I've found this especially useful for certain types of repository (like Gentoo's ebuild repositories) because files are often copies of a previous version.

These must be very small repositories? --find-copies-harder is really expensive...

Quoted 5 lines

Documentation/config/diff.txt +0 -0

index bd5ae0c3378..d2ff3c62d41 100644
@@ -131,7 +131,8 @@ diff.renames::

Documentation/config/diff.txt diff.renames:: · line 135

Quoted 6 lines

Documentation/config/diff.txt +2 -1

        Whether and how Git detects renames.  If set to "false",
        rename detection is disabled. If set to "true", basic rename
        detection is enabled.  If set to "copies" or "copy", Git will
-       detect copies, as well.  Defaults to true.  Note that this
+       detect copies, as well.  If set to "copies-harder", Git will try harder
+       to detect copies.  Defaults to true.  Note that this

"try harder to detect copies" feels like an unhelpful explanation.

Quoted 12 lines · Elijah Newren

Quoted 10 lines · Sam James via GitGitGadget

From: Sam James <[email protected]>

This patch adds a config value for 'diff.renames' called 'copies-harder' which make it so '-C -C' is in effect always passed for 'git log -p', 'git diff', etc.

This allows specifying that 'git log -p', 'git diff', etc should always act as if '-C --find-copies-harder' was passed.

Quoted 6 lines

Quoted 3 lines

I've found this especially useful for certain types of repository (like Gentoo's ebuild repositories) because files are often copies of a previous version.

These must be very small repositories? --find-copies-harder is really expensive...

True. "often copies of a previous version" means that it is a directory that has a collection of subdirectories, one for each version? In a source tree managed in a version control system, files are often rewritten in place from the previous version, so I am puzzled by that justification.

It is, in the proposed log message of our commits, a bit unusual to see "This patch does X" and "I do Y", by the way, which made my reading hiccup a bit, but perhaps it is just me?

Quoted 5 lines

Quoted 5 lines

Documentation/config/diff.txt +0 -0

index bd5ae0c3378..d2ff3c62d41 100644
@@ -131,7 +131,8 @@ diff.renames::

Quoted 8 lines

Documentation/config/diff.txt diff.renames:: · line 135

Quoted 6 lines

Documentation/config/diff.txt +2 -1

        Whether and how Git detects renames.  If set to "false",
        rename detection is disabled. If set to "true", basic rename
        detection is enabled.  If set to "copies" or "copy", Git will
-       detect copies, as well.  Defaults to true.  Note that this
+       detect copies, as well.  If set to "copies-harder", Git will try harder
+       to detect copies.  Defaults to true.  Note that this

"try harder to detect copies" feels like an unhelpful explanation.

Yup. "will spend extra cycles to find more copies", perhaps?

Quoted 9 lines

True. "often copies of a previous version" means that it is a directory that has a collection of subdirectories, one for each version? In a source tree managed in a version control system, files are often rewritten in place from the previous version, so I am puzzled by that justification.

It is, in the proposed log message of our commits, a bit unusual to see "This patch does X" and "I do Y", by the way, which made my reading hiccup a bit, but perhaps it is just me?

I think I read Sam's description a bit differently than you. My assumption was they'd have files with names like the following in the same directory:

   gcc-13.x.build.recipe
   gcc-12.x.build.recipe
   gcc-11.x.build.recipe
   gcc-10.x.build.recipe

And that gcc-13.x.build.recipe was started as a copy of gcc-12.x.build.recipe (which was started as a copy of gcc-11.x.build.recipe, etc.). They keep all versions because they want users to be able to build and install multiple gcc versions.

I find that marginally better; but I still don't think it answers the user's question of why they should pick one option or the other. The wording for the --find-copies-harder does explain when it's useful:

For performance reasons, by default, -C option finds copies only if the original file of the copy was modified in the same changeset. This flag makes the command
inspect unmodified files as candidates for the source of copy. This is a very expensive operation for large projects, so use it with caution.

We probably don't want to copy all three of those sentences here, but I think we need to make sure users can find them, thus my suggestion to reference the --find-copies-harder option to git-diff so that affected users can get the info they need to choose.

Quoted 11 lines · Elijah Newren

I find that marginally better; but I still don't think it answers the user's question of why they should pick one option or the other. The wording for the --find-copies-harder does explain when it's useful:

For performance reasons, by default, -C option finds copies only if the original file of the copy was modified in the same changeset. This flag makes the command
inspect unmodified files as candidates for the source of copy. This is a very expensive operation for large projects, so use it with caution.

Quoted 4 lines

We probably don't want to copy all three of those sentences here, but I think we need to make sure users can find them, thus my suggestion to reference the --find-copies-harder option to git-diff so that affected users can get the info they need to choose.

"in addition to paths that are different, will look for more copies even in unmodified paths" then?

Quoted 7 lines

Quoted 4 lines

We probably don't want to copy all three of those sentences here, but I think we need to make sure users can find them, thus my suggestion to reference the --find-copies-harder option to git-diff so that affected users can get the info they need to choose.

"in addition to paths that are different, will look for more copies even in unmodified paths" then?

That's much better. I still slightly prefer referencing --find-copies-harder so that there's a link between "copies-harder" and --find-copies-harder; but this version would also be fine.

Quoted 11 lines · Elijah Newren

Quoted 7 lines

Quoted 4 lines

We probably don't want to copy all three of those sentences here, but I think we need to make sure users can find them, thus my suggestion to reference the --find-copies-harder option to git-diff so that affected users can get the info they need to choose.

"in addition to paths that are different, will look for more copies even in unmodified paths" then?

That's much better. I still slightly prefer referencing --find-copies-harder so that there's a link between "copies-harder" and --find-copies-harder; but this version would also be fine.

Oh, I didn't mean "use this rewrite and do not make any external reference". More like "external reference is a good idea and necessary to help motivated readers, but we should give enough information inline, and I think this level of details would be sufficient".

From: Sam James <[email protected]>

This patch adds a config value for 'diff.renames' called 'copies-harder' which make it so '-C -C' is in effect always passed for 'git log -p', 'git diff', etc.

This allows specifying that 'git log -p', 'git diff', etc should always act as if '-C --find-copies-harder' was passed.

I've found this especially useful for certain types of repository (like Gentoo's ebuild repositories) because files are often copies of a previous version.

Signed-off-by Sam James <[email protected]>

---
diff: implement config.diff.renames=copies-harder

This patch adds a config value for 'diff.renames' called 'copies-harder' which make it so '-C -C' is in effect always passed for 'git log -p', 'git diff', etc.

This allows specifying that 'git log -p', 'git diff', etc should always act as if '-C --find-copies-harder' was passed.

I've found this especially useful for certain types of repository (like Gentoo's ebuild repositories) because files are often copies of a previous version.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1606%2Fthesamesam%2Fconfig-copies-harder-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1606/thesamesam/config-copies-harder-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1606