rebase: dereference tags

Thanks for the comments on V2. Here are the changes from that version:

* dropped the controversial cleanup that was patch 8
* reworded patch 10 as suggested by Junio

Cover letter for v2: Thanks to Ævar and Johannes for their comments.

* Changed "! test_cmp_rev" to "test_cmp_rev !" (suggested by Ævar)
* Fixed the quoting for the title of the "rebase --quit" tests.
* Reworked the last commit to handle the error case first (suggested by Ævar)
* Tweaked the commit messages for patches 8 & 11
* Rebased onto 31e4a0db03 ("Merge branch 'ab/rebase-fatal-fatal-fix'", 2021-09-08) to avoid a merge conflict that upset gitgitgadget

Cover letter for V1: Aborting a rebase stated with git rebase <upstream> <tag-object> should checkout the commit pointed to by . Instead it gives

error: update_ref failed for ref 'HEAD': cannot update ref 'HEAD': trying to write non-commit object 710d743b2b9892457fdcc3970f397e6ec07447e0 to branch 'HEAD'

The fix for that is in the last patch, the rest of the patches are cleanups to t3407 and builtin/rebase.c

Phillip Wood (10):
t3407: run tests in $TEST_DIRECTORY
t3407: use test_commit
t3407: use test_cmp_rev
t3407: rename a variable
t3407: use test_path_is_missing
t3407: strengthen rebase --abort tests
t3407: rework rebase --quit tests
rebase: use our standard error return value
rebase: use lookup_commit_reference_by_name()
rebase: dereference tags

 builtin/rebase.c        |  49 ++++++++-----------
 t/t3407-rebase-abort.sh | 105 ++++++++++++++++++----------------------
 2 files changed, 67 insertions(+), 87 deletions(-)

base-commit: 31e4a0db0337e2aa972d9b9f11a332dff7c4cbcb
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1033%2Fphillipwood%2Fwip%2Frebase-handle-tags-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1033/phillipwood/wip/rebase-handle-tags-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/1033

Range-diff vs v2:

  1:  bac009d8543 =  1:  bac009d8543 t3407: run tests in $TEST_DIRECTORY
  2:  abfffb31a56 =  2:  abfffb31a56 t3407: use test_commit
  3:  7755ce17fef =  3:  7755ce17fef t3407: use test_cmp_rev
  4:  38eee11baf5 =  4:  38eee11baf5 t3407: rename a variable
  5:  61a37c89f1e =  5:  61a37c89f1e t3407: use test_path_is_missing
  6:  6866630528b =  6:  6866630528b t3407: strengthen rebase --abort tests
  7:  fd55a3196b1 =  7:  fd55a3196b1 t3407: rework rebase --quit tests
  8:  ad3c4efc027 <  -:  ----------- rebase: remove redundant strbuf
  9:  ad940b633d0 !  8:  d3af62c746c rebase: use our standard error return value
     @@ builtin/rebase.c: int cmd_rebase(int argc, const char **argv, const char *prefix
       		} else if (!(options.flags & REBASE_NO_QUIET))
       			; /* be quiet */
      @@ builtin/rebase.c: int cmd_rebase(int argc, const char **argv, const char *prefix)
     - 		reset_head(the_repository, NULL, "Fast-forwarded", options.head_name,
     - 			   RESET_HEAD_REFS_ONLY, "HEAD", buf.buf,
     + 			   RESET_HEAD_REFS_ONLY, "HEAD", msg.buf,
       			   DEFAULT_REFLOG_ACTION);
     + 		strbuf_release(&msg);
      -		ret = !!finish_rebase(&options);
      +		ret = finish_rebase(&options);
       		goto cleanup;
 10:  bc103e703e8 =  9:  4eedd3ae766 rebase: use lookup_commit_reference_by_name()
 11:  951de6bb199 ! 10:  55a6250ab38 rebase: dereference tags

@@ Metadata
## Commit message ##
rebase: dereference tags

- Aborting a rebase stated with 'git rebase <upstream> <tag-object>'
- should checkout the commit pointed to by <tag-object>. Instead it gives
+ A rebase started with 'git rebase <A> <B>' is conceptually to first
+ checkout <B> and run 'git rebase <A>' starting from that state. 'git
+ rebase --abort' in the middle of such a rebase should take us back to
+ the state we checked out <B>.

- error: update_ref failed for ref 'HEAD': cannot update ref 'HEAD':
- trying to write non-commit object
- 710d743b2b9892457fdcc3970f397e6ec07447e0 to branch 'HEAD'
+ This used to work, even when <B> is a tag that points at a commit,
+ until Git 2.20.0 when the command was reimplemented in C. The command
+ now complains that the tag object itself cannot be checked out, which
+ may be technically correct but is not what the user asked to do.

- This is because when we parse the command line arguments although we
- check that the tag points to a commit we remember the oid of the tag
- and try and checkout that object rather than the commit it points
- to. Fix this by using lookup_commit_reference_by_name() when parsing
- the command line.
+ Fix this old regression by using lookup_commit_reference_by_name()
+ when parsing <B>. The scripted version did not need to peel the tag
+ because the commands it passed the tag to (e.g 'git reset') peeled the
+ tag themselves.

---

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