refs: split internal and external references

Currently libgit2 shares pointers to its internal reference cache with
the user. This leads to several problems like invalidation of reference
pointers when reordering the cache or manipulation of the cache from
user side.

Give each user its own git_reference instead of leaking the internal
representation (struct reference).

Add the following new API functions:

	* git_reference_free
	* git_reference_is_packed

Signed-off-by: schu <schu-github@schulog.org>

include/git2/refs.h

@@ -23,8 +23,7 @@ GIT_BEGIN_DECL
 /**
  * Lookup a reference by its name in a repository.
  *
- * The generated reference is owned by the repository and
- * should not be freed by the user.
+ * The generated reference must be freed by the user.
  *
  * @param reference_out pointer to the looked-up reference
  * @param repo the repository to look up the reference
@@ -39,8 +38,7 @@ GIT_EXTERN(int) git_reference_lookup(git_reference **reference_out, git_reposito
  * The reference will be created in the repository and written
  * to the disk.
  *
- * This reference is owned by the repository and shall not
- * be free'd by the user.
+ * The generated reference must be freed by the user.
  *
  * If `force` is true and there already exists a reference
  * with the same name, it will be overwritten.
@@ -60,8 +58,7 @@ GIT_EXTERN(int) git_reference_create_symbolic(git_reference **ref_out, git_repos
  * The reference will be created in the repository and written
  * to the disk.
  *
- * This reference is owned by the repository and shall not
- * be free'd by the user.
+ * The generated reference must be freed by the user.
  *
  * If `force` is true and there already exists a reference
  * with the same name, it will be overwritten.
@@ -173,7 +170,9 @@ GIT_EXTERN(int) git_reference_set_oid(git_reference *ref, const git_oid *id);
  * The new name will be checked for validity and may be
  * modified into a normalized form.
  *
- * The refernece will be immediately renamed in-memory
+ * The given git_reference will be updated.
+ *
+ * The reference will be immediately renamed in-memory
  * and on disk.
  *
  */
@@ -200,9 +199,6 @@ GIT_EXTERN(int) git_reference_delete(git_reference *ref);
  * Once the `packed-refs` file has been written properly,
  * the loose references will be removed from disk.
  *
- * WARNING: calling this method may invalidate any existing
- * references previously loaded on the cache.
- *
  * @param repo Repository where the loose refs will be packed
  * @return GIT_SUCCESS or an error code
  */
@@ -253,6 +249,21 @@ GIT_EXTERN(int) git_reference_listall(git_strarray *array, git_repository *repo,
  */
 GIT_EXTERN(int) git_reference_foreach(git_repository *repo, unsigned int list_flags, int (*callback)(const char *, void *), void *payload);
 
+/**
+ * Check if a reference is packed
+ *
+ * @param ref git_reference
+ * @return 0 in case it's not packed; 1 otherwise
+ */
+GIT_EXTERN(int) git_reference_is_packed(git_reference *ref);
+
+/**
+ * Free the given reference
+ *
+ * @param ref git_reference
+ */
+GIT_EXTERN(void) git_reference_free(git_reference *ref);
+
 /** @} */
 GIT_END_DECL
 #endif

src/commit.c

@@ -137,12 +137,13 @@ int git_commit_create(
 
 	if (error == GIT_SUCCESS && update_ref != NULL) {
 		git_reference *head;
+		git_reference *target;
 
 		error = git_reference_lookup(&head, repo, update_ref);
 		if (error < GIT_SUCCESS)
 			return git__rethrow(error, "Failed to create commit");
 
-		error = git_reference_resolve(&head, head);
+		error = git_reference_resolve(&target, head);
 		if (error < GIT_SUCCESS) {
 			if (error != GIT_ENOTFOUND)
 				return git__rethrow(error, "Failed to create commit");
@@ -156,7 +157,7 @@ int git_commit_create(
 			return git_reference_create_oid(&head, repo, git_reference_target(head), oid, 1);
 		}
 
-		error = git_reference_set_oid(head, oid);
+		error = git_reference_set_oid(target, oid);
 	}
 
 	if (error < GIT_SUCCESS)

src/refs.h

@@ -35,8 +35,6 @@
 struct git_reference {
 	git_repository *owner;
 	char *name;
-	unsigned int type;
-	time_t mtime;
 };
 
 typedef struct {