Properly peel tags in can_all_from_reach_with_flags()

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)
---

5c5,7
< from_one = deref_tag(the_repository, from_one, "a from object", 0);
---

14a17,22

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/[email protected]/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 <[email protected]>

- 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.
+

@@ -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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