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

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