From: Philippe Blain <levraiphilippeblain@gmail.com>
Using `git checkout --recurse-submodules` to switch between a branch with no submodules and a branch with initialized nested submodules currently causes a fatal error:
$ git checkout --recurse-submodules branch-with-nested-submodules
fatal: exec '--super-prefix=submodule/nested/': cd to 'nested'
failed: No such file or directory
error: Submodule 'nested' could not be updated.
error: Submodule 'submodule/nested' cannot checkout new HEAD.
error: Submodule 'submodule' could not be updated.
M submodule
Switched to branch 'branch-with-nested-submodules'The checkout succeeds but the worktree and index of the first level submodule are left empty:
$ cd submodule
$ git -c status.submoduleSummary=1 status
HEAD detached at b3ce885
Changes to be committed:
(use "git restore --staged <file>..." to unstage)
deleted: .gitmodules
deleted: first.t
deleted: nested fatal: not a git repository: 'nested/.git'
Submodule changes to be committed: * nested 1e96f59...0000000:
$ git ls-files -s
$ # empty
$ ls -A
.gitThe reason for the fatal error during the checkout is that a child git process tries to cd into the yet unexisting nested submodule directory. The sequence is the following:
1. The main git process (the one running in the superproject) eventually
reaches write_entry() in entry.c, which creates the first level
submodule directory and then calls submodule_move_head() in submodule.c,
which spawns `git read-tree` in the submodule directory.
2. The first child git process (the one in the submodule of the
superproject) eventually calls check_submodule_move_head() at
unpack_trees.c:2021, which calls submodule_move_head in dry-run mode,
which spawns `git read-tree` in the nested submodule directory.
3. The second child git process tries to chdir() in the yet unexisting
nested submodule directory in start_command() at run-command.c:829 and
dies before exec'ing.
The reason why check_submodule_move_head() is reached in the first child and not in the main process is that it is inside an if(submodule_from_ce()) construct, and submodule_from_ce() returns a valid struct submodule pointer, whereas it returns a null pointer in the main git process.
The reason why submodule_from_ce() returns a null pointer in the main git process is because the call to cache_lookup_path() in config_from() (called from submodule_from_path() in submodule_from_ce()) returns a null pointer since the hashmap "for_path" in the submodule_cache of the_repository is not yet populated. It is not populated because both repo_get_oid(repo, GITMODULES_INDEX, &oid) and repo_get_oid(repo, GITMODULES_HEAD, &oid) in config_from_gitmodules() at submodule-config.c:639-640 return -1, as at this stage of the operation, neither the HEAD of the superproject nor its index contain any .gitmodules file.
In contrast, in the first child the hashmap is populated because repo_get_oid(repo, GITMODULES_HEAD, &oid) returns 0 as the HEAD of the first level submodule, i.e. .git/modules/submodule/HEAD, points to a commit where .gitmodules is present and records 'nested' as a submodule.
Fix this bug by checking that the submodule directory exists before calling check_submodule_move_head() in merged_entry() in the `if(!old)` branch, i.e. if going from a commit with no submodule to a commit with a submodule present.
Also protect the other call to check_submodule_move_head() in merged_entry() the same way as it is safer, even though the `else if (!(old->ce_flags & CE_CONFLICTED))` branch of the code is not at play in the present bug.
The other calls to check_submodule_move_head() in other functions in unpack_trees.c are all already protected by calls to lstat() somewhere in the program flow so we don't need additional protection for them.
All commands in the unpack_trees machinery are affected, i.e. checkout, reset and read-tree when called with the --recurse-submodules flag.
This bug was first reported in [1].
[1] https://lore.kernel.org/git/7437BB59-4605-48EC-B05E-E2BDB2D9DABC@gmail.com/
Reported-by: Philippe Blain <levraiphilippeblain@gmail.com>
Reported-by: Damien Robert <damien.olivier.robert@gmail.com>
Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
---
t/lib-submodule-update.sh | 14 ++++++++++++++
unpack-trees.c | 4 ++--
2 files changed, 16 insertions(+), 2 deletions(-)
Show changes to 2 files +16 −2
t/lib-submodule-update.sh, unpack-trees.c
diff --git a/t/lib-submodule-update.sh b/t/lib-submodule-update.sh
index 417da3602ae..ab30b2da24f 100755
--- a/t/lib-submodule-update.sh
+++ b/t/lib-submodule-update.sh
@@ -626,6 +626,7 @@ test_submodule_forced_switch () {
# New test cases
# - Removing a submodule with a git directory absorbs the submodules
# git directory first into the superproject.
+# - Switching from no submodule to nested submodules
# Internal function; use test_submodule_switch_recursing_with_args() or
# test_submodule_forced_switch_recursing_with_args() instead.
@@ -683,6 +684,19 @@ test_submodule_recursing_with_args_common() {
test_submodule_content sub1 origin/replace_directory_with_sub1
)
'
+ # Switching to a commit with nested submodules recursively checks them out
+ test_expect_success "$command: nested submodules are checked out" '
+ prolog &&
+ reset_work_tree_to_interested no_submodule &&
+ (
+ cd submodule_update &&
+ git branch -t modify_sub1_recursively origin/modify_sub1_recursively &&
+ $command modify_sub1_recursively &&
+ test_superproject_content origin/modify_sub1_recursively &&
+ test_submodule_content sub1 origin/modify_sub1_recursively &&
+ test_submodule_content -C sub1 sub2 origin/modify_sub1_recursively
+ )
+ '
######################## Disappearing submodule #######################
# Removing a submodule removes its work tree ...
diff --git a/unpack-trees.c b/unpack-trees.c
index 37eca3ede8b..fc6ba19486d 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -2064,7 +2064,7 @@ static int merged_entry(const struct cache_entry *ce,
}
invalidate_ce_path(merge, o);
- if (submodule_from_ce(ce)) {
+ if (submodule_from_ce(ce) && file_exists(ce->name)) {
int ret = check_submodule_move_head(ce, NULL,
oid_to_hex(&ce->oid),
o);
@@ -2093,7 +2093,7 @@ static int merged_entry(const struct cache_entry *ce,
invalidate_ce_path(old, o);
}
- if (submodule_from_ce(ce)) {
+ if (submodule_from_ce(ce) && file_exists(ce->name)) {
int ret = check_submodule_move_head(ce, oid_to_hex(&old->oid),
oid_to_hex(&ce->oid),
o);
Philippe Blain via GitGitGadget