[PATCH v2 5/6] submodule: improve submodule_has_commits

[Brandon Williams <bmwill@google.com>]

Teach 'submodule_has_commits()' to ensure that if a commit exists in a
submodule, that it is also reachable from a ref.

This is a preparatory step prior to merging the logic which checks for
changed submodules when fetching or pushing.

Change-Id: I4fed2acfa7e69a5fbbca534df165671e77a90f22
Signed-off-by: Brandon Williams <bmwill@google.com>
---
 submodule.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/submodule.c b/submodule.c
index 3bcf44521..057695e64 100644
--- a/submodule.c
+++ b/submodule.c
@@ -644,10 +644,44 @@ static int submodule_has_commits(const char *path, struct oid_array *commits)
 {
 	int has_commit = 1;
 
+	/*
+	 * Perform a cheap, but incorrect check for the existance of 'commits'.
+	 * This is done by adding the submodule's object store to the in-core
+	 * object store, and then querying for each commit's existance.  If we
+	 * do not have the commit object anywhere, there is no chance we have
+	 * it in the object store of the correct submodule and have it
+	 * reachable from a ref, so we can fail early without spawning rev-list
+	 * which is expensive.
+	 */
 	if (add_submodule_odb(path))
 		return 0;
 
 	oid_array_for_each_unique(commits, check_has_commit, &has_commit);
+
+	if (has_commit) {
+		/*
+		 * Even if the submodule is checked out and the commit is
+		 * present, make sure it exists in the submodule's object store
+		 * and that it is reachable from a ref.
+		 */
+		struct child_process cp = CHILD_PROCESS_INIT;
+		struct strbuf out = STRBUF_INIT;
+
+		argv_array_pushl(&cp.args, "rev-list", "-n", "1", NULL);
+		oid_array_for_each_unique(commits, append_oid_to_argv, &cp.args);
+		argv_array_pushl(&cp.args, "--not", "--all", NULL);
+
+		prepare_submodule_repo_env(&cp.env_array);
+		cp.git_cmd = 1;
+		cp.no_stdin = 1;
+		cp.dir = path;
+
+		if (capture_command(&cp, &out, GIT_MAX_HEXSZ + 1) || out.len)
+			has_commit = 0;
+
+		strbuf_release(&out);
+	}
+
 	return has_commit;
 }
 
-- 
2.13.0.rc1.294.g07d810a77f-goog