[PATCH v4 0/6] merge-tree: handle missing objects correctly

Johannes Schindelin via GitGitGadget
2024-02-23T08:34:30Z

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 v3:

* Aligned the translated error messages with pre-existing ones (sorry, I
forgot to make that change in v2!).
* Added a new commit at the end to mark the one error message for
translation which I had imitated, after making it consistent with the
remaining "unable to read tree" error messages.

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 (6):
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
fill_tree_descriptor(): mark error message for translation

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 +++++++++++++++++++++++++++
t/t6030-bisect-porcelain.sh | 2 +-
tree-walk.c | 2 +-
15 files changed, 89 insertions(+), 17 deletions(-)

base-commit: 5f43cf5b2e4b68386d3774bce880b0f74d801635
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1651%2Fdscho%2Fmerge-tree-and-missing-objects-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1651/dscho/merge-tree-and-missing-objects-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/1651

Range-diff vs v3:

1: 11b9cd8c5da = 1: 11b9cd8c5da merge-tree: fail with a non-zero exit code on missing tree objects
2: f01f4eb011b = 2: f01f4eb011b merge-ort: do check `parse_tree()`'s return value
3: e82fdf7fbcb = 3: e82fdf7fbcb t4301: verify that merge-tree fails on missing blob objects
4: 9e4dc94ef03 ! 4: 5942c27f439 Always check `parse_tree*()`'s return value
@@ builtin/checkout.c: static int merge_working_tree(const struct checkout_opts *op
new_tree = repo_get_commit_tree(the_repository,
new_branch_info->commit);
+ if (!new_tree)
-+ return error(_("unable to read tree %s"),
++ return error(_("unable to read tree (%s)"),
+ oid_to_hex(&new_branch_info->commit->object.oid));
+ }
if (opts->discard_changes) {
@@ builtin/checkout.c: static void setup_new_branch_info_and_source_tree(
/* not a commit */
*source_tree = parse_tree_indirect(rev);
+ if (!*source_tree)
-+ die(_("unable to read tree %s"), oid_to_hex(rev));
++ die(_("unable to read tree (%s)"), oid_to_hex(rev));
} else {
parse_commit_or_die(new_branch_info->commit);
*source_tree = repo_get_commit_tree(the_repository,
new_branch_info->commit);
+ if (!*source_tree)
-+ die(_("unable to read tree %s"),
++ die(_("unable to read tree (%s)"),
+ oid_to_hex(&new_branch_info->commit->object.oid));
}
}
@@ builtin/merge-tree.c: static int real_merge(struct merge_tree_options *o,
die(_("could not parse as tree '%s'"), merge_base);
base_tree = parse_tree_indirect(&base_oid);
+ if (!base_tree)
-+ die(_("unable to read tree %s"), oid_to_hex(&base_oid));
++ die(_("unable to read tree (%s)"), oid_to_hex(&base_oid));
if (repo_get_oid_treeish(the_repository, branch1, &head_oid))
die(_("could not parse as tree '%s'"), branch1);
parent1_tree = parse_tree_indirect(&head_oid);
+ if (!parent1_tree)
-+ die(_("unable to read tree %s"), oid_to_hex(&head_oid));
++ die(_("unable to read tree (%s)"), oid_to_hex(&head_oid));
if (repo_get_oid_treeish(the_repository, branch2, &merge_oid))
die(_("could not parse as tree '%s'"), branch2);
parent2_tree = parse_tree_indirect(&merge_oid);
+ if (!parent2_tree)
-+ die(_("unable to read tree %s"), oid_to_hex(&merge_oid));
++ die(_("unable to read tree (%s)"), oid_to_hex(&merge_oid));

opt.ancestor = merge_base;
merge_incore_nonrecursive(&opt, base_tree, parent1_tree, parent2_tree, &result);
@@ builtin/reset.c: static int reset_index(const char *ref, const struct object_id
if (reset_type == MIXED || reset_type == HARD) {
tree = parse_tree_indirect(oid);
+ if (!tree) {
-+ error(_("unable to read tree %s"), oid_to_hex(oid));
++ error(_("unable to read tree (%s)"), oid_to_hex(oid));
+ goto out;
+ }
prime_cache_tree(the_repository, the_repository->index, tree);
@@ merge-ort.c: static void merge_ort_nonrecursive_internal(struct merge_options *o
if (result->clean >= 0) {
result->tree = parse_tree_indirect(&working_tree_oid);
+ if (!result->tree)
-+ die(_("unable to read tree %s"),
++ die(_("unable to read tree (%s)"),
+ oid_to_hex(&working_tree_oid));
/* existence of conflicted entries implies unclean */
result->clean &= strmap_empty(&opt->priv->conflicted);
@@ reset.c: int reset_head(struct repository *r, const struct reset_head_opts *opts

tree = parse_tree_indirect(oid);
+ if (!tree) {
-+ ret = error(_("unable to read tree %s"), oid_to_hex(oid));
++ ret = error(_("unable to read tree (%s)"), oid_to_hex(oid));
+ goto leave_reset_head;
+ }
+
@@ sequencer.c: static int do_recursive_merge(struct repository *r,

head_tree = parse_tree_indirect(head);
+ if (!head_tree)
-+ return error(_("unable to read tree %s"), oid_to_hex(head));
++ return error(_("unable to read tree (%s)"), oid_to_hex(head));
next_tree = next ? repo_get_commit_tree(r, next) : empty_tree(r);
base_tree = base ? repo_get_commit_tree(r, base) : empty_tree(r);

@@ sequencer.c: static int do_reset(struct repository *r,

tree = parse_tree_indirect(&oid);
+ if (!tree)
-+ return error(_("unable to read tree %s"), oid_to_hex(&oid));
++ return error(_("unable to read tree (%s)"), oid_to_hex(&oid));
prime_cache_tree(r, r->index, tree);

if (write_locked_index(r->index, &lock, COMMIT_LOCK) < 0)
5: 91dc4ccd04e = 5: 7e5e84a4e7c cache-tree: avoid an unnecessary check
-: ----------- > 6: ee2fcee5a10 fill_tree_descriptor(): mark error message for translation