Submodule caching fix and location API

This adds a new API to the submodule interface that just returns
where information about the submodule was found (e.g. config file
only or in the HEAD, index, or working directory).

Also, the old "refresh" call was potentially keeping some stale
submodule data around, so this simplfies that code and literally
discards the old cache, then reallocates.

include/git2/submodule.h

@@ -504,6 +504,24 @@ GIT_EXTERN(int) git_submodule_status(
 	unsigned int *status,
 	git_submodule *submodule);
 
+/**
+ * Get the locations of submodule information.
+ *
+ * This is a bit like a very lightweight version of `git_submodule_status`.
+ * It just returns a made of the first four submodule status values (i.e.
+ * the ones like GIT_SUBMODULE_STATUS_IN_HEAD, etc) that tell you where the
+ * submodule data comes from (i.e. the HEAD commit, gitmodules file, etc.).
+ * This can be useful if you want to know if the submodule is present in the
+ * working directory at this point in time, etc.
+ *
+ * @param status Combination of first four `GIT_SUBMODULE_STATUS` flags
+ * @param submodule Submodule for which to get status
+ * @return 0 on success, <0 on error
+ */
+GIT_EXTERN(int) git_submodule_location(
+	unsigned int *location_status,
+	git_submodule *submodule);
+
 /** @} */
 GIT_END_DECL
 #endif

src/submodule.c

@@ -66,7 +66,7 @@ __KHASH_IMPL(
 	str, static kh_inline, const char *, void *, 1,
 	str_hash_no_trailing_slash, str_equal_no_trailing_slash);
 
-static int load_submodule_config(git_repository *repo, bool force);
+static int load_submodule_config(git_repository *repo);
 static git_config_backend *open_gitmodules(git_repository *, bool, const git_oid *);
 static int lookup_head_remote(git_buf *url, git_repository *repo);
 static int submodule_get(git_submodule **, git_repository *, const char *, const char *);
@@ -106,7 +106,7 @@ int git_submodule_lookup(
 
 	assert(repo && name);
 
-	if ((error = load_submodule_config(repo, false)) < 0)
+	if ((error = load_submodule_config(repo)) < 0)
 		return error;
 
 	pos = git_strmap_lookup_index(repo->submodules, name);
@@ -148,7 +148,7 @@ int git_submodule_foreach(
 
 	assert(repo && callback);
 
-	if ((error = load_submodule_config(repo, false)) < 0)
+	if ((error = load_submodule_config(repo)) < 0)
 		return error;
 
 	git_strmap_foreach_value(repo->submodules, sm, {
@@ -708,7 +708,8 @@ int git_submodule_open(
 int git_submodule_reload_all(git_repository *repo)
 {
 	assert(repo);
-	return load_submodule_config(repo, true);
+	git_submodule_config_free(repo);
+	return load_submodule_config(repo);
 }
 
 int git_submodule_reload(git_submodule *submodule)
@@ -829,6 +830,20 @@ int git_submodule_status(
 	return error;
 }
 
+int git_submodule_location(
+	unsigned int *location_status,
+	git_submodule *submodule)
+{
+	assert(location_status && submodule);
+
+	*location_status = submodule->flags &
+		(GIT_SUBMODULE_STATUS_IN_HEAD | GIT_SUBMODULE_STATUS_IN_INDEX |
+		 GIT_SUBMODULE_STATUS_IN_CONFIG | GIT_SUBMODULE_STATUS_IN_WD);
+
+	return 0;
+}
+
+
 /*
  * INTERNAL FUNCTIONS
  */
@@ -1225,14 +1240,14 @@ static git_config_backend *open_gitmodules(
 	return mods;
 }
 
-static int load_submodule_config(git_repository *repo, bool force)
+static int load_submodule_config(git_repository *repo)
 {
 	int error;
 	git_oid gitmodules_oid;
 	git_buf path = GIT_BUF_INIT;
 	git_config_backend *mods = NULL;
 
-	if (repo->submodules && !force)
+	if (repo->submodules)
 		return 0;
 
 	memset(&gitmodules_oid, 0, sizeof(gitmodules_oid));