libgit2 · ethomson · Jan 21, 2017 · Nov 23, 2016 · Nov 23, 2016 · Nov 23, 2016
diff --git a/include/git2/sys/repository.h b/include/git2/sys/repository.h
@@ -135,6 +135,35 @@ GIT_EXTERN(void) git_repository_set_index(git_repository *repo, git_index *index
  */
 GIT_EXTERN(int) git_repository_set_bare(git_repository *repo);
 
+/**
+ * Load and cache all submodules.
+ *
+ * Because the `.gitmodules` file is unstructured, loading submodules is an
+ * O(N) operation.  Any operation (such as `git_rebase_init`) that requires
+ * accessing all submodules is O(N^2) in the number of submodules, if it
+ * has to look each one up individually.  This function loads all submodules
+ * and caches them so that subsequent calls to `git_submodule_lookup` are O(1).
+ *
+ * @param repo the repository whose submodules will be cached.
+ */
+GIT_EXTERN(int) git_repository_submodule_cache_all(
+	git_repository *repo);
+
+/**
+ * Clear the submodule cache.
+ *
+ * Clear the submodule cache populated by `git_repository_submodule_cache_all`.
+ * If there is no cache, do nothing.
+ *
+ * The cache incorporates data from the repository's configuration, as well
+ * as the state of the working tree, the index, and HEAD.  So any time any
+ * of these has changed, the cache might become invalid.
+ *
+ * @param repo the repository whose submodule cache will be cleared
+ */
+GIT_EXTERN(int) git_repository_submodule_cache_clear(
+	git_repository *repo);
+
 /** @} */
 GIT_END_DECL
 #endif
diff --git a/src/repository.c b/src/repository.c
@@ -27,6 +27,10 @@
 #include "merge.h"
 #include "diff_driver.h"
 #include "annotated_commit.h"
+#include "submodule.h"
+
+GIT__USE_STRMAP
+#include "strmap.h"
 
 #ifdef GIT_WIN32
 # include "win32/w32_util.h"
@@ -109,6 +113,7 @@ void git_repository__cleanup(git_repository *repo)
 {
 	assert(repo);
 
+	git_repository_submodule_cache_clear(repo);
 	git_cache_clear(&repo->objects);
 	git_attr_cache_flush(repo);
 
@@ -2541,3 +2546,31 @@ int git_repository_set_ident(git_repository *repo, const char *name, const char
 
 	return 0;
 }
+
+int git_repository_submodule_cache_all(git_repository *repo)
+{
+	int error;
+
+	assert(repo);
+
+	if ((error = git_strmap_alloc(&repo->submodule_cache)))
+		return error;
+
+	error = git_submodule__map(repo, repo->submodule_cache);
+	return error;
+}
+
+int git_repository_submodule_cache_clear(git_repository *repo)
+{
+	git_submodule *sm;
+	assert(repo);
+	if (repo->submodule_cache == NULL) {
+		return 0;
+	}
+	git_strmap_foreach_value(repo->submodule_cache, sm, {
+		git_submodule_free(sm);
+	});
+	git_strmap_free(repo->submodule_cache);
+	repo->submodule_cache = 0;
+	return 0;
+}
diff --git a/src/repository.h b/src/repository.h
@@ -143,6 +143,7 @@ struct git_repository {
 	git_atomic attr_session_key;
 
 	git_cvar_value cvar_cache[GIT_CVAR_CACHE_MAX];
+	git_strmap *submodule_cache;
 };
 
 GIT_INLINE(git_attr_cache *) git_repository_attr_cache(git_repository *repo)