[PATCH v6 5/5] submodule: use config to find superproject worktree

[Emily Shaffer <emilyshaffer@google.com>]

Now that submodule.superprojectGitDir is being treated as the point of
truth for whether a repo is a submodule or not, let's use it in `git
rev-parse --show-superproject-working-tree`.

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>

---

This commit may be more of an RFC - to demonstrate what life looks like
if we use submodule.superprojectGitDir as the source of truth. But since
'git rev-parse --show-superproject-working-tree' is used in a lot of
scripts in the wild[1], I'm not so sure it's a great example.

To be honest, I'd prefer to die("Try running 'git submodule update'")
here, but I don't think that's very script-friendly. However, falling
back on the old implementation kind of undermines the idea of treating
submodule.superprojectGitDir as the point of truth. One thought I did
have was to put that error message in builtin/rev-parse.c instead, and
print it to stderr (per usual with user-visible messages) so it doesn't
interfere with scripts, but gives a hint for debugging.

Another thought - captured by the NEEDSWORK in the diff - was that we
could "heal" by adding that config after we know the worktree of the
superproject.

Or, it could be that it won't be a problem for a long time, as anybody
running 'git submodule update' will eventually have that config
specified - that's why I included the traces, so we could try and get an
understanding of how long repos remain in this state where they have
submodules but nobody ran 'git submodule update'. But that will only
give me visibility into submodule users at Google, who we expect to be
making a lot of workflow changes soon, anyway.

1: https://github.com/search?q=%22--show-superproject-working-tree%22&type=code
---
 submodule.c          | 85 +++++++++++++++++++++++++++++++++++++++++++-
 t/t1500-rev-parse.sh |  9 +++++
 2 files changed, 93 insertions(+), 1 deletion(-)

diff --git a/submodule.c b/submodule.c
index d7395c7551..ad95cdda07 100644
--- a/submodule.c
+++ b/submodule.c
@@ -2236,7 +2236,7 @@ void absorb_git_dir_into_superproject(const char *path,
 	}
 }
 
-int get_superproject_working_tree(struct strbuf *buf)
+static int get_superproject_working_tree_from_fs(struct strbuf *buf)
 {
 	struct child_process cp = CHILD_PROCESS_INIT;
 	struct strbuf sb = STRBUF_INIT;
@@ -2320,6 +2320,89 @@ int get_superproject_working_tree(struct strbuf *buf)
 	return ret;
 }
 
+int get_superproject_working_tree(struct strbuf *buf)
+{
+	char *super_gitdir = NULL;
+	const char *cwd = xgetcwd();
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf absolute_super_gitdir = STRBUF_INIT;
+	struct strbuf out = STRBUF_INIT;
+	struct string_list lines = STRING_LIST_INIT_NODUP;
+	struct string_list_item *it = NULL;
+	const char *wt_prefix = "worktree ";
+	int rc = 0;
+
+
+	/* Do we know we have a superproject? */
+	if (git_config_get_string("submodule.superprojectgitdir", &super_gitdir))
+		goto fallback;
+
+	strbuf_addf(&absolute_super_gitdir, "%s/%s", get_git_dir(), super_gitdir);
+
+	/*
+	 * NEEDSWORK: This is a child process call because worktree.c still
+	 * relies heavily on the_repository. If we can make worktree.c work with
+	 * a repository object - or, better yet, a gitdir path alone - then we
+	 * can drop the child process and ask worktree.c directly.
+	 *
+	 * Alternatively, if 'git worktree' learns a way to say 'the worktree
+	 * associated with this gitdir' instead of 'all worktrees', that would
+	 * be clearer because we could skip the foreach below.
+	 */
+
+	/* Get the output of `git worktree list` from that superproject */
+	prepare_other_repo_env(&cp.env_array, absolute_super_gitdir.buf);
+	strvec_pushl(&cp.args, "-C", absolute_super_gitdir.buf, "worktree", "list",
+		    "--porcelain", NULL);
+
+	cp.git_cmd = 1;
+	if (capture_command(&cp, &out, 0) ||
+	    !string_list_split_in_place(&lines, out.buf, '\n', -1))
+		die("submodule.superprojectGitDir is stale; run 'git submodule "
+		    "update' from the superproject.");
+
+	for_each_string_list_item(it, &lines) {
+		char *trimmed;
+		/*
+		 * Lines containing worktree dirs look like
+		 * 'worktree /some/path'
+		 */
+		if (strncmp(it->string, wt_prefix, strlen(wt_prefix)))
+			continue;
+		trimmed = it->string + strlen(wt_prefix);
+
+		/*
+		 * '/some/path/to/sub' is a prefix of '/some/path' - that's our
+		 * worktree
+		 */
+		if (!strncmp(cwd, trimmed, strlen(trimmed))) {
+			strbuf_addstr(buf, trimmed);
+			rc = 1;
+			goto cleanup;
+		}
+	}
+
+fallback:
+	/*
+	 * Because a submodule may have been created before
+	 * submodule.superprojectGitDir was introduced, fall back on checking
+	 * whether ../ is the superproject.
+	 */
+	trace2_data_intmax("submodule", the_repository,
+			   "get_superproject_wt/config_missing", rc);
+	rc = get_superproject_working_tree_from_fs(buf);
+
+	/*
+	 * NEEDSWORK: Is it possible to teach a submodule the path to its
+	 * superproject when this happens?
+	 */
+
+cleanup:
+	string_list_clear(&lines, 0);
+	strbuf_release(&out);
+	return rc;
+}
+
 /*
  * Put the gitdir for a submodule (given relative to the main
  * repository worktree) into `buf`, or return -1 on error.
diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
index 1c2df08333..e569910289 100755
--- a/t/t1500-rev-parse.sh
+++ b/t/t1500-rev-parse.sh
@@ -247,6 +247,15 @@ test_expect_success 'showing the superproject correctly' '
 	test_cmp expect out
 '
 
+test_expect_success 'show the superproject correctly without superprojectGitDir' '
+	# repos created before submodule.superprojectGitDir was introduced which
+	# have not been `git submodule update`-ed lately must not break
+	git -C super/dir/sub config --unset submodule.superprojectGitDir &&
+	echo $(pwd)/super >expect &&
+	git -C super/dir/sub rev-parse --show-superproject-working-tree >out &&
+	test_cmp expect out
+'
+
 # at least one external project depends on this behavior:
 test_expect_success 'rev-parse --since= unsqueezed ordering' '
 	x1=--since=1970-01-01T00:00:01Z &&
-- 
2.34.0.rc1.387.gb447b232ab-goog