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mingw: align symlinks-related rmdir() behavior with Linux 

When performing a rebase, rmdir() is called on the folder .git/logs. On
Unix rmdir() exits without deleting anything in case .git/logs is a
symbolic link but the equivalent functions on Windows (_rmdir, _wrmdir
and RemoveDirectoryW) do not behave the same and remove the folder if it
is symlinked even if it is not empty.

This creates issues when folders in .git/ are symlinks which is
especially the case when git-repo[1] is used: It replaces `.git/logs/`
with a symlink.

One such issue is that the _target_ of that symlink is removed e.g.
during a `git rebase`, where `delete_reflog("REBASE_HEAD")` will not
only try to remove `.git/logs/REBASE_HEAD` but then recursively try to
remove the parent directories until an error occurs, a technique that
obviously relies on `rmdir()` refusing to remove a symlink.

This was reported in https://github.com/git-for-windows/git/issues/2967.

This commit updates mingw_rmdir() so that its behavior is the same as
Linux rmdir() in case of symbolic links.

To verify that Git does not regress on the reported issue, this patch
adds a regression test for the `git rebase` symptom, even if the same
`rmdir()` behavior is quite likely to cause potential problems in other
Git commands as well.

[1]: git-repo is a python tool built on top of Git which helps manage
many Git repositories. It stores all the .git/ folders in a central
place by taking advantage of symbolic links.
More information: https://gerrit.googlesource.com/git-repo/

Signed-off-by: Thomas Bétous <tomspycell@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Thomas Bétous 2021-08-02 21:07:30 +00:00 committed by Junio C Hamano
parent ebf3c04b26
commit 3e7d4888e5
3 changed files with 37 additions and 0 deletions
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21
compat/mingw.c
View File

@ -341,6 +341,27 @@ int mingw_rmdir(const char *pathname)
{
int ret, tries = 0;
wchar_t wpathname[MAX_PATH];
struct stat st;
/*
* Contrary to Linux' `rmdir()`, Windows' _wrmdir() and _rmdir()
* (and `RemoveDirectoryW()`) will attempt to remove the target of a
* symbolic link (if it points to a directory).
*
* This behavior breaks the assumption of e.g. `remove_path()` which
* upon successful deletion of a file will attempt to remove its parent
* directories recursively until failure (which usually happens when
* the directory is not empty).
*
* Therefore, before calling `_wrmdir()`, we first check if the path is
* a symbolic link. If it is, we exit and return the same error as
* Linux' `rmdir()` would, i.e. `ENOTDIR`.
*/
if (!mingw_lstat(pathname, &st) && S_ISLNK(st.st_mode)) {
errno = ENOTDIR;
return -1;
}
if (xutftowcs_path(wpathname, pathname) < 0)
return -1;

10
t/t3400-rebase.sh
View File

@ -406,4 +406,14 @@ test_expect_success 'refuse to switch to branch checked out elsewhere' '
test_i18ngrep "already checked out" err
'
test_expect_success MINGW,SYMLINKS_WINDOWS 'rebase when .git/logs is a symlink' '
git checkout main &&
mv .git/logs actual_logs &&
cmd //c "mklink /D .git\logs ..\actual_logs" &&
git rebase -f HEAD^ &&
test -L .git/logs &&
rm .git/logs &&
mv actual_logs .git/logs
'
test_done

6
t/test-lib.sh
View File

@ -1513,6 +1513,12 @@ test_lazy_prereq SYMLINKS '
ln -s x y && test -h y
'
test_lazy_prereq SYMLINKS_WINDOWS '
# test whether symbolic links are enabled on Windows
test_have_prereq MINGW &&
cmd //c "mklink y x" &> /dev/null && test -h y
'
test_lazy_prereq FILEMODE '
test "$(git config --bool core.filemode)" = true
'