From: Kyle Zhao <kylezhao@xxxxxxxxxxx>
When running a merge while the index is locked (presumably by another
process), the merge state is written, the index is not updated, and then
the merge fails. This can cause unexpected results.
i.g. if another running process is "git commit", MERGE_HEAD and other state
files we write on our side will be taken into account by them and cause them
to record a merge, even though they may have been trying to record something
entirely different.
Signed-off-by: Kyle Zhao <kylezhao@xxxxxxxxxxx>
---
merge: avoid write merge state when unable to write index
In some of our monorepos, code is sometimes lost after merging.
After investigation, we discovered the problem.
This happens if we perform "git pull" or "git merge" when another git
process is writing to the index, especially in a monorepo (because its
index will be larger).
How to reproduce:
git init demo
cd demo
touch 1.txt && git add . && git commit -m "1"
git checkout -b source-branch
touch 2.txt && git add . && git commit -m "2"
git checkout master
echo "1" >> 1.txt && git add . && git commit -m "3"
# another git process runnning
touch .git/index.lock
git merge source-branch
# another git process finished
rm .git/index.lock
git commit -m "4"
Then the modifications from the source branch are lost.
Regards, Kyle
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1731%2Fkeyu98%2Fkz%2Ffix-merge-when-index-lock-exists-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1731/keyu98/kz/fix-merge-when-index-lock-exists-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/1731
Range-diff vs v2:
1: 86101e5b778 ! 1: 138fe0a054d merge: avoid write merge state when unable to write index
@@ Metadata
## Commit message ##
merge: avoid write merge state when unable to write index
- Currently, when index.lock exists, if a merge occurs, the merge state
- will be written and the index will be unchanged.
+ When running a merge while the index is locked (presumably by another
+ process), the merge state is written, the index is not updated, and then
+ the merge fails. This can cause unexpected results.
- If the user exec "git commit" instead of "git merge --abort" after this,
- a merge commit will be generated and all modifications from the source
- branch will be lost.
+ i.g. if another running process is "git commit", MERGE_HEAD and other state
+ files we write on our side will be taken into account by them and cause them
+ to record a merge, even though they may have been trying to record something
+ entirely different.
Signed-off-by: Kyle Zhao <kylezhao@xxxxxxxxxxx>
## builtin/merge.c ##
@@ builtin/merge.c: static int try_merge_strategy(const char *strategy, struct commit_list *common,
-
if (repo_refresh_and_write_index(the_repository, REFRESH_QUIET,
SKIP_IF_UNCHANGED, 0, NULL, NULL,
-- NULL) < 0)
+ NULL) < 0)
- return error(_("Unable to write index."));
-+ NULL) < 0) {
-+ error(_("Unable to write index."));
-+ return 2;
-+ }
++ die(_("Unable to write index."));
if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree") ||
!strcmp(strategy, "ort")) {
@@ t/t7600-merge.sh: test_expect_success 'merge c1 with c2' '
+test_expect_success 'merge c1 with c2 when index.lock exists' '
+ test_when_finished rm .git/index.lock &&
+ git reset --hard c1 &&
-+ touch .git/index.lock &&
++ : >.git/index.lock &&
+ test_must_fail git merge c2 &&
+ test_path_is_missing .git/MERGE_HEAD &&
+ test_path_is_missing .git/MERGE_MODE &&
builtin/merge.c | 2 +-
t/t7600-merge.sh | 10 ++++++++++
2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/builtin/merge.c b/builtin/merge.c
index 6a6d3798858..12c1b048fe1 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -699,7 +699,7 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
if (repo_refresh_and_write_index(the_repository, REFRESH_QUIET,
SKIP_IF_UNCHANGED, 0, NULL, NULL,
NULL) < 0)
- return error(_("Unable to write index."));
+ die(_("Unable to write index."));
if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree") ||
!strcmp(strategy, "ort")) {
diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
index e5ff073099a..c1958095dcf 100755
--- a/t/t7600-merge.sh
+++ b/t/t7600-merge.sh
@@ -236,6 +236,16 @@ test_expect_success 'merge c1 with c2' '
verify_parents $c1 $c2
'
+test_expect_success 'merge c1 with c2 when index.lock exists' '
+ test_when_finished rm .git/index.lock &&
+ git reset --hard c1 &&
+ : >.git/index.lock &&
+ test_must_fail git merge c2 &&
+ test_path_is_missing .git/MERGE_HEAD &&
+ test_path_is_missing .git/MERGE_MODE &&
+ test_path_is_missing .git/MERGE_MSG
+'
+
test_expect_success 'merge --squash c3 with c7' '
git reset --hard c3 &&
test_must_fail git merge --squash c7 &&
base-commit: 19fe900cfce8096b7645ec9611a0b981f6bbd154
--
gitgitgadget
