[PATCH v2 0/5] merge-tree: handle missing objects correctly

Johannes Schindelin via GitGitGadget
2024-02-07T16:47:45Z

I recently looked into issues where git merge-tree calls returned bogus data
(in one instance returning an empty tree for non-empty merge parents). By
the time I had a look at the corresponding repository, the issue was no
longer reproducible, but a closer look at the code combined with some manual
experimenting turned up the fact that missing tree objects aren't handled as
errors by git merge-tree.

While at it, I added a commit on top that tries to catch all remaining
unchecked parse_tree() calls.

This patch series is based on js/merge-tree-3-trees because I introduced
three unchecked parse_tree() calls in that topic branch.

Changes since v1:

* Simplified the test case, avoiding a subshell and a pipe in the process.
* Added a patch to remove a superfluous subtree->object.parsed guard around
a parse_tree(subtree) call.

Johannes Schindelin (5):
merge-tree: fail with a non-zero exit code on missing tree objects
merge-ort: do check `parse_tree()`'s return value
t4301: verify that merge-tree fails on missing blob objects
Always check `parse_tree*()`'s return value
cache-tree: avoid an unnecessary check

builtin/checkout.c | 19 ++++++++++++++++---
builtin/clone.c | 3 ++-
builtin/commit.c | 3 ++-
builtin/merge-tree.c | 6 ++++++
builtin/read-tree.c | 3 ++-
builtin/reset.c | 4 ++++
cache-tree.c | 4 ++--
merge-ort.c | 16 +++++++++++-----
merge-recursive.c | 3 ++-
merge.c | 5 ++++-
reset.c | 5 +++++
sequencer.c | 4 ++++
t/t4301-merge-tree-write-tree.sh | 24 ++++++++++++++++++++++++
13 files changed, 84 insertions(+), 15 deletions(-)

base-commit: 5f43cf5b2e4b68386d3774bce880b0f74d801635
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1651%2Fdscho%2Fmerge-tree-and-missing-objects-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1651/dscho/merge-tree-and-missing-objects-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1651

Range-diff vs v1:

1: a3e8ae86114 ! 1: 01dfd66568c merge-tree: fail with a non-zero exit code on missing tree objects
@@ merge-ort.c: static int collect_merge_info(struct merge_options *opt,

## t/t4301-merge-tree-write-tree.sh ##
@@ t/t4301-merge-tree-write-tree.sh: test_expect_success '--merge-base with tree OIDs' '
- git merge-tree --merge-base=side1^^{tree} side1^{tree} side3^{tree} >with-trees &&
test_cmp with-commits with-trees
'
+
+test_expect_success 'error out on missing tree objects' '
+ git init --bare missing-tree.git &&
-+ (
-+ git rev-list side3 &&
-+ git rev-parse side3^:
-+ ) | git pack-objects missing-tree.git/objects/pack/side3-tree-is-missing &&
++ git rev-list side3 >list &&
++ git rev-parse side3^: >list &&
++ git pack-objects missing-tree.git/objects/pack/side3-tree-is-missing <list &&
+ side3=$(git rev-parse side3) &&
+ test_must_fail git --git-dir=missing-tree.git merge-tree $side3^ $side3 >actual &&
+ test_must_be_empty actual
+'
-
++
test_done
2: 3e5b787fc03 = 2: a1bbb7e06e5 merge-ort: do check `parse_tree()`'s return value
3: 85d3e672871 = 3: be1dadf2850 t4301: verify that merge-tree fails on missing blob objects
4: 93abd7000b8 = 4: ffd38ad602a Always check `parse_tree*()`'s return value
-: ----------- > 5: 43c04749513 cache-tree: avoid an unnecessary check