submodules: add helper to determine if a submodule is populated

Add the `is_submodule_populated()` helper function to submodules.c.
`is_submodule_populated()` performes a check to see if a submodule has
been checkout out (and has a valid .git directory/file) at the given path.

Signed-off-by: Brandon Williams <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: bmwill

submodule.c

@@ -198,6 +198,21 @@ void gitmodules_config(void)
 	}
 }
 
+/*
+ * Determine if a submodule has been populated at a given 'path'
+ */
+int is_submodule_populated(const char *path)
+{
+	int ret = 0;
+	char *gitdir = xstrfmt("%s/.git", path);
+
+	if (resolve_gitdir(gitdir))
+		ret = 1;
+
+	free(gitdir);
+	return ret;
+}
+
 int parse_submodule_update_strategy(const char *value,
 		struct submodule_update_strategy *dst)
 {

submodule.h

@@ -37,6 +37,7 @@ void set_diffopt_flags_from_submodule_config(struct diff_options *diffopt,
 		const char *path);
 int submodule_config(const char *var, const char *value, void *cb);
 void gitmodules_config(void);
+extern int is_submodule_populated(const char *path);
 int parse_submodule_update_strategy(const char *value,
 		struct submodule_update_strategy *dst);
 const char *submodule_strategy_to_string(const struct submodule_update_strategy *s);