rebase --keep-base: imply --reapply-cherry-picks and --no-fork-point

A while a go Philippe reported [1] that he was surprised 'git rebase --keep-base' removed commits that had been cherry-picked upstream even though to branch was not being rebased. I think it is also surprising if '--keep-base' changes the base of the branch without '--fork-point' being explicitly given on the command line. This series therefore changes the default behavior of '--keep-base' to imply '--reapply-cherry-picks' and '--no-fork-point' so that the base of the branch is unchanged and no commits are removed.

Thanks to Junio and Ævar for their comments, the changes since V3 are:

* Patch 3: added lookup_commit_object() that works like lookup_commit_reference() but without dereferencing tags.
* Patch 4: changed lookup_commit_reference() to lookup_commit_object()
* Patch 5: unchanged - Ævar has concerns about renaming merge_base to branch_base but I think this is an improvement overall.
* Patches 6 & 8: fixed a whitespace issue

Thanks to Junio for his comments, the changes since V2 are:

* Patch 3 new patch to make sure we're reading hex oids from state files
* Patch 4 restored the call to read_refs() to avoid the dwim behavior of lookup_commit_reference_by_name()
* Patch 6 added a comment to clarify what a null oid branch_base means

Thanks to everyone who commented for their reviews, the changes since V1 are:

* Patch 1: new patch to tighten a couple of existing tests
* Patch 2: reworded commit message in response to Junio's comments
* Patch 3: fixed a typo in the commit message spotted by Elijah and tidied code formatting
* Patch 4: new patch to rename a variable suggested by Junio
* Patch 5: clarified commit message and removed some redundant code spotted by Junio
* Patch 6: improved --reapply-cherry-picks documentation to mention --keep-base and vice-versa suggested by Philippe
* Patch 7: expanded the commit message and documentation in response to Junio's comments

[1]
https://lore.kernel.org/git/[email protected]/

Phillip Wood (8):
t3416: tighten two tests
t3416: set $EDITOR in subshell
rebase: be stricter when reading state files containing oids
rebase: store orig_head as a commit
rebase: rename merge_base to branch_base
rebase: factor out branch_base calculation
rebase --keep-base: imply --reapply-cherry-picks rebase --keep-base: imply --no-fork-point

 Documentation/git-rebase.txt     |  32 ++++---
 builtin/rebase.c                 | 144 ++++++++++++++++++-------------
 commit.c                         |   8 ++
 commit.h                         |  13 +++
 t/t3416-rebase-onto-threedots.sh |  62 ++++++++++---
 t/t3431-rebase-fork-point.sh     |   2 +-
 6 files changed, 172 insertions(+), 89 deletions(-)

base-commit: afa70145a25e81faa685dc0b465e52b45d2444bd
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1323%2Fphillipwood%2Fwip%2Frebase--keep-base-tweaks-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1323/phillipwood/wip/rebase--keep-base-tweaks-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/1323

Range-diff vs v3:

 1:  12fb0ac6d5d = 1:  12fb0ac6d5d t3416: tighten two tests
 2:  d6f2f716c77 = 2:  d6f2f716c77 t3416: set $EDITOR in subshell
 3:  1fd58520253 ! 3:  1d5e0419c45 rebase: be stricter when reading state files containing oids

@@ Commit message

The state files for 'onto' and 'orig_head' should contain a full hex oid, change the reading functions from get_oid() to get_oid_hex() to
- reflect this.
+ reflect this. They should also name commits and not tags so add and use
+ a function that looks up a commit from an oid like
+ lookup_commit_reference() but without dereferencing tags.

@@ builtin/rebase.c: static int read_basic_state(struct rebase_options *opts)
xstrdup(head_name.buf) : NULL;
strbuf_release(&head_name);
- if (get_oid(buf.buf, &oid))
-+ if (get_oid_hex(buf.buf, &oid))
- return error(_("could not get 'onto': '%s'"), buf.buf);
- opts->onto = lookup_commit_or_die(&oid, buf.buf);
+- return error(_("could not get 'onto': '%s'"), buf.buf);
+- opts->onto = lookup_commit_or_die(&oid, buf.buf);
++ if (get_oid_hex(buf.buf, &oid) ||
++ !(opts->onto = lookup_commit_object(the_repository, &oid)))
++ return error(_("invalid onto: '%s'"), buf.buf);

+ /*
+ * We always write to orig-head, but interactive rebase used to write to
@@ builtin/rebase.c: static int read_basic_state(struct rebase_options *opts)
} else if (!read_oneliner(&buf, state_dir_path("head", opts),
READ_ONELINER_WARN_MISSING))
@@ builtin/rebase.c: static int read_basic_state(struct rebase_options *opts)
return error(_("invalid orig-head: '%s'"), buf.buf);

if (file_exists(state_dir_path("quiet", opts)))
+
+ ## commit.c ##
+@@ commit.c: struct commit *lookup_commit_or_die(const struct object_id *oid, const char *ref
+ return c;
+ }
+
++struct commit *lookup_commit_object (struct repository *r,
++ const struct object_id *oid)
++{
++ struct object *obj = parse_object(r, oid);
++ return obj ? object_as_type(obj, OBJ_COMMIT, 0) : NULL;
++
++}
++
+ struct commit *lookup_commit(struct repository *r, const struct object_id *oid)
+ {
+ struct object *obj = lookup_object(r, oid);
+
+ ## commit.h ##
+@@ commit.h: enum decoration_type {
+ void add_name_decoration(enum decoration_type type, const char *name, struct object *obj);
+ const struct name_decoration *get_name_decoration(const struct object *obj); +
++/*
++ * Look up commit named by "oid" respecting replacement objects.
++ * Returns NULL if "oid" is not a commit or does not exist.
++ */
++struct commit *lookup_commit_object(struct repository *r, const struct object_id *oid); ++
++/*
++ * Look up commit named by "oid" without replacement objects or
++ * checking for object existence. Returns the requested commit if it
++ * is found in the object cache, NULL if "oid" is in the object cache
++ * but is not a commit and a newly allocated unparsed commit object if
++ * "oid" is not in the object cache.
++ */
+ struct commit *lookup_commit(struct repository *r, const struct object_id *oid);
+ struct commit *lookup_commit_reference(struct repository *r,
+ const struct object_id *oid);
4: dc056b13ed5 ! 4: 22f3d265b57 rebase: store orig_head as a commit
@@ Commit message
oid to a commit.

To avoid changing the behavior of "git rebase <upstream> <branch>" we
- keep the existing call to read_ref() and use lookup_commit_reference()
+ keep the existing call to read_ref() and use lookup_commit_object()
on the oid returned by that rather than calling lookup_commit_reference_by_name() which applies the ref dwim rules to
- its argument. lookup_commit_reference() will dereference tag objects
- but we do not expect the branch being rebased to be pointing to a tag
- object.
+ its argument.

@@ builtin/rebase.c: static int read_basic_state(struct rebase_options *opts)
return -1;
- if (get_oid_hex(buf.buf, &opts->orig_head))
+ if (get_oid_hex(buf.buf, &oid) ||
-+ !(opts->orig_head = lookup_commit_reference(the_repository, &oid)))
++ !(opts->orig_head = lookup_commit_object(the_repository, &oid)))
return error(_("invalid orig-head: '%s'"), buf.buf);

if (file_exists(state_dir_path("quiet", opts)))
@@ builtin/rebase.c: int cmd_rebase(int argc, const char **argv, const char *prefix
die_if_checked_out(buf.buf, 1);
options.head_name = xstrdup(buf.buf);
+ options.orig_head =
-+ lookup_commit_reference(the_repository,
-+ &branch_oid);
++ lookup_commit_object(the_repository,
++ &branch_oid);
/* If not is it a valid ref (branch or commit)? */
} else {
- struct commit *commit =

 5:  00f70c90344 = 5:  79a8c0fe284 rebase: rename merge_base to branch_base
 6:  2efbfc94187 ! 6:  bd24409a266 rebase: factor out branch_base calculation
     @@ builtin/rebase.c: int cmd_rebase(int argc, const char **argv, const char *prefix
       				options.onto_name);
      +		fill_branch_base(&options, &branch_base);
       	}
     --
     + 
       	if (options.fork_point > 0)
     - 		options.restrict_revision =
     - 			get_fork_point(options.upstream_name, options.orig_head);
      @@ builtin/rebase.c: int cmd_rebase(int argc, const char **argv, const char *prefix)
       	 * Check if we are already based on onto with linear history,
       	 * in which case we could fast-forward without replacing the commits
 7:  bc39c76b217 ! 7:  367e44c6928 rebase --keep-base: imply --reapply-cherry-picks
     @@ builtin/rebase.c: int cmd_rebase(int argc, const char **argv, const char *prefix
       
       	if (gpg_sign)
      @@ builtin/rebase.c: int cmd_rebase(int argc, const char **argv, const char *prefix)
     - 				options.onto_name);
       		fill_branch_base(&options, &branch_base);
       	}
     + 
      +	if (keep_base && options.reapply_cherry_picks)
      +		options.upstream = options.onto;
      +

8: 4d0226e1dcc = 8: 656b9c9dab6 rebase --keep-base: imply --no-fork-point

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