msubprojects: fix potential error when resetting a git checkout

Untracked files need to be stashed too, or resetting may fail when
trying to (re-)apply a patch that adds one of those untracked files.

mesonbuild/msubprojects.py

@@ -207,13 +207,16 @@ class Runner:
         self.log(self.git_output(cmd))
 
     def git_stash(self) -> None:
-        # That git command return 1 (failure) when there is something to stash.
+        # That git command return some output when there is something to stash.
         # We don't want to stash when there is nothing to stash because that would
         # print spurious "No local changes to save".
-        if not quiet_git(['diff', '--quiet', 'HEAD'], self.repo_dir)[0]:
+        if quiet_git(['status', '--porcelain', ':!/.meson-subproject-wrap-hash.txt'], self.repo_dir)[1].strip():
             # Don't pipe stdout here because we want the user to see their changes have
             # been saved.
-            self.git_verbose(['stash'])
+            # Note: `--all` is used, and not `--include-untracked`, to prevent
+            # a potential error if `.meson-subproject-wrap-hash.txt` matches a
+            # gitignore pattern.
+            self.git_verbose(['stash', 'push', '--all', ':!/.meson-subproject-wrap-hash.txt'])
 
     def git_show(self) -> None:
         commit_message = self.git_output(['show', '--quiet', '--pretty=format:%h%n%d%n%s%n[%an]'])

unittests/subprojectscommandtests.py

@@ -177,6 +177,17 @@ class SubprojectsCommandTests(BasePlatformTests):
         self.assertEqual(self._git_local_commit(subp_name), self._git_remote_commit(subp_name, 'newbranch'))
         self.assertTrue(self._git_local(['stash', 'list'], subp_name))
 
+        # Untracked files need to be stashed too, or (re-)applying a patch
+        # creating one of those untracked files will fail.
+        untracked = self.subprojects_dir / subp_name / 'untracked.c'
+        untracked.write_bytes(b'int main(void) { return 0; }')
+        self._subprojects_cmd(['update', '--reset'])
+        self.assertTrue(self._git_local(['stash', 'list'], subp_name))
+        assert not untracked.exists()
+        # Ensure it was indeed stashed, and we can get it back.
+        self.assertTrue(self._git_local(['stash', 'pop'], subp_name))
+        assert untracked.exists()
+
         # Create a new remote tag and update the wrap file. Checks that
         # "meson subprojects update --reset" checkout the new tag in detached mode.
         self._git_create_remote_tag(subp_name, 'newtag')