[PATCH v4 0/1] Properly peel tags in can_all_from_reach_with_flags()

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

As Peff reported [1], the refactored can_all_from_reach_with_flags() method
does not properly peel tags. Since the helper method can_all_from_reach()
and code in t/helper/test-reach.c all peel tags before getting to this
method, it is not super-simple to create a test that demonstrates this.

I modified t/helper/test-reach.c to allow calling
can_all_from_reach_with_flags() directly, and added a test in
t6600-test-reach.sh that demonstrates the segfault without the fix.

For V2, I compared the loop that inspects the 'from' commits in commit
ba3ca1edce "commit-reach: move can_all_from_reach_with_flags" to the version
here and got the following diff:

3c3
<                 if (from_one->flags & assign_flag)
---
>                 if (!from_one || from_one->flags & assign_flag)
5c5,7
<                 from_one = deref_tag(the_repository, from_one, "a from object", 0);
---
>
>                 from_one = deref_tag(the_repository, from_one,
>                                      "a from object", 0);
14a17,22
>
>                 list[nr_commits] = (struct commit *)from_one;
>                 if (parse_commit(list[nr_commits]) ||
>                     list[nr_commits]->generation < min_generation)
>                         return 0; /* is this a leak? */
>                 nr_commits++;

This diff includes the early termination we had before 'deref_tag' and the
comment for why we can ignore non-commit objects.

[1] 
https://public-inbox.org/git/0bf9103c-9377-506b-7ad7-e5273d8e94fc@gmail.com/T/#u

Derrick Stolee (1):
  commit-reach: properly peel tags and clear flags

 commit-reach.c        | 44 +++++++++++++++++++++++++++++++++----------
 t/helper/test-reach.c | 22 +++++++++++++++++-----
 t/t6600-test-reach.sh | 30 +++++++++++++++++++++++++++--
 3 files changed, 79 insertions(+), 17 deletions(-)


base-commit: 6621c838743812aaba96e55cfec8524ea1144c2d
Published-As: https://github.com/gitgitgadget/git/releases/tags/pr-39%2Fderrickstolee%2Ftag-fix-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-39/derrickstolee/tag-fix-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/39

Range-diff vs v3:

 1:  0a1e661271 ! 1:  a0a3cf0134 commit-reach: properly peel tags
     @@ -1,6 +1,6 @@
      Author: Derrick Stolee <dstolee@microsoft.com>
      
     -    commit-reach: properly peel tags
     +    commit-reach: properly peel tags and clear flags
      
          The can_all_from_reach_with_flag() algorithm was refactored in 4fbcca4e
          "commit-reach: make can_all_from_reach... linear" but incorrectly
     @@ -14,6 +14,19 @@
          Correct the issue by peeling tags when investigating the initial list
          of objects in the 'from' array.
      
     +    The can_all_from_reach_with_flag() method uses 'assign_flag' as a
     +    value we can use to mark objects temporarily during our commit walk.
     +    The intent is that these flags are removed from all objects before
     +    returning. However, this is not the case.
     +
     +    The 'from' array could also contain objects that are not commits, and
     +    we mark those objects with 'assign_flag'. Add a loop to the 'cleanup'
     +    section that removes these markers.
     +
     +    Also, we forgot to free() the memory for 'list', so add that to the
     +    'cleanup' section. Also, use a cleaner mechanism for clearing those
     +    flags.
     +
          Signed-off-by: Jeff King <peff@peff.net>
          Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
      
     @@ -74,10 +87,18 @@
       
       cleanup:
      -	for (i = 0; i < from->nr; i++) {
     -+	for (i = 0; i < nr_commits; i++) {
     - 		clear_commit_marks(list[i], RESULT);
     - 		clear_commit_marks(list[i], assign_flag);
     - 	}
     +-		clear_commit_marks(list[i], RESULT);
     +-		clear_commit_marks(list[i], assign_flag);
     +-	}
     ++	clear_commit_marks_many(nr_commits, list, RESULT | assign_flag);
     ++	free(list);
     ++
     ++	for (i = 0; i < from->nr; i++)
     ++		from->objects[i].item->flags &= ~assign_flag;
     ++
     + 	return result;
     + }
     + 
      
      diff --git a/t/helper/test-reach.c b/t/helper/test-reach.c
      --- a/t/helper/test-reach.c
 2:  b2e0ee4978 < -:  ---------- commit-reach: fix memory and flag leaks

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