[PATCH v3 0/5] merge-tree: handle missing objects correctly

Johannes Schindelin via GitGitGadget
2024-02-22T14:36:49Z

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 5f43cf5b2e4 (merge-tree: accept 3 trees as
arguments, 2024-01-28) (the original tip commit of js/merge-tree-3-trees)
because I introduced three unchecked parse_tree() calls in that topic.

Changes since v2:

* Fixed the new "missing tree object" test case in t4301 that succeeded for
the wrong reason.
* Adjusted the new "missing blob object" test case to avoid succeeding for
the wrong reason.
* Simplified the "missing blob object" test case.

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 | 27 +++++++++++++++++++++++++++
13 files changed, 87 insertions(+), 15 deletions(-)

base-commit: 5f43cf5b2e4b68386d3774bce880b0f74d801635
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1651%2Fdscho%2Fmerge-tree-and-missing-objects-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1651/dscho/merge-tree-and-missing-objects-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/1651

Range-diff vs v2:

1: 01dfd66568c ! 1: 11b9cd8c5da merge-tree: fail with a non-zero exit code on missing tree objects
@@ t/t4301-merge-tree-write-tree.sh: test_expect_success '--merge-base with tree OI
+test_expect_success 'error out on missing tree objects' '
+ git init --bare missing-tree.git &&
+ git rev-list side3 >list &&
-+ git rev-parse 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_fail git --git-dir=missing-tree.git merge-tree $side3^ $side3 >actual 2>err &&
++ test_grep "Could not read $(git rev-parse $side3:)" err &&
+ test_must_be_empty actual
+'
+
2: a1bbb7e06e5 = 2: f01f4eb011b merge-ort: do check `parse_tree()`'s return value
3: be1dadf2850 ! 3: e82fdf7fbcb t4301: verify that merge-tree fails on missing blob objects
@@ t/t4301-merge-tree-write-tree.sh: test_expect_success 'error out on missing tree
'

+test_expect_success 'error out on missing blob objects' '
-+ seq1=$(test_seq 1 10 | git hash-object -w --stdin) &&
-+ seq2=$(test_seq 1 11 | git hash-object -w --stdin) &&
-+ seq3=$(test_seq 0 10 | git hash-object -w --stdin) &&
-+ tree1=$(printf "100644 blob %s\tsequence" $seq1 | git mktree) &&
-+ tree2=$(printf "100644 blob %s\tsequence" $seq2 | git mktree) &&
-+ tree3=$(printf "100644 blob %s\tsequence" $seq3 | git mktree) &&
++ echo 1 | git hash-object -w --stdin >blob1 &&
++ echo 2 | git hash-object -w --stdin >blob2 &&
++ echo 3 | git hash-object -w --stdin >blob3 &&
++ printf "100644 blob $(cat blob1)\tblob\n" | git mktree >tree1 &&
++ printf "100644 blob $(cat blob2)\tblob\n" | git mktree >tree2 &&
++ printf "100644 blob $(cat blob3)\tblob\n" | git mktree >tree3 &&
+ git init --bare missing-blob.git &&
-+ test_write_lines $seq1 $seq3 $tree1 $tree2 $tree3 |
++ cat blob1 blob3 tree1 tree2 tree3 |
+ git pack-objects missing-blob.git/objects/pack/side1-whatever-is-missing &&
-+ test_must_fail git --git-dir=missing-blob.git merge-tree --merge-base=$tree1 $tree2 $tree3 >actual &&
++ test_must_fail git --git-dir=missing-blob.git >actual 2>err \
++ merge-tree --merge-base=$(cat tree1) $(cat tree2) $(cat tree3) &&
++ test_grep "unable to read blob object $(cat blob2)" err &&
+ test_must_be_empty actual
+'
+
4: ffd38ad602a = 4: 9e4dc94ef03 Always check `parse_tree*()`'s return value
5: 43c04749513 = 5: 91dc4ccd04e cache-tree: avoid an unnecessary check