Add git_reference_lookup_oid and lookup_resolved

Adds a new public reference function `git_reference_lookup_oid`
that directly resolved a reference name to an OID without returning
the intermediate `git_reference` object (hence, no free needed).

Internally, this adds a `git_reference_lookup_resolved` function
that combines looking up and resolving a reference.  This allows
us to be more efficient with memory reallocation.

The existing `git_reference_lookup` and `git_reference_resolve`
are reimplmented on top of the new utility and a few places in the
code are changed to use one of the two new functions.

include/git2/refs.h

@@ -33,6 +33,16 @@ GIT_BEGIN_DECL
 GIT_EXTERN(int) git_reference_lookup(git_reference **reference_out, git_repository *repo, const char *name);
 
 /**
+ * Lookup a reference by name and resolve immediately to OID.
+ *
+ * @param oid Pointer to oid to be filled in
+ * @param repo The repository in which to look up the reference
+ * @param name The long name for the reference
+ * @return 0 on success, -1 if name could not be resolved
+ */
+GIT_EXTERN(int) git_reference_lookup_oid(git_oid *out, git_repository *repo, const char *name);
+
+/**
  * Create a new symbolic reference.
  *
  * The reference will be created in the repository and written
@@ -304,6 +314,15 @@ GIT_EXTERN(int) git_reference_reload(git_reference *ref);
  */
 GIT_EXTERN(void) git_reference_free(git_reference *ref);
 
+/**
+ * Compare two references.
+ *
+ * @param ref1 The first git_reference
+ * @param ref2 The second git_reference
+ * @return GIT_SUCCESS if the same, else a stable but meaningless ordering.
+ */
+GIT_EXTERN(int) git_reference_cmp(git_reference *ref1, git_reference *ref2);
+
 /** @} */
 GIT_END_DECL
 #endif

src/refs.c

@@ -15,7 +15,8 @@
 #include <git2/tag.h>
 #include <git2/object.h>
 
-#define MAX_NESTING_LEVEL 5
+#define DEFAULT_NESTING_LEVEL	5
+#define MAX_NESTING_LEVEL		10
 
 enum {
 	GIT_PACKREF_HAS_PEEL = 1,
@@ -1057,24 +1058,80 @@ int git_reference_delete(git_reference *ref)
 int git_reference_lookup(git_reference **ref_out,
 	git_repository *repo, const char *name)
 {
-	char normalized_name[GIT_REFNAME_MAX];
-	git_reference *ref = NULL;
-	int result;
+	return git_reference_lookup_resolved(ref_out, repo, name, 0);
+}
+
+int git_reference_lookup_oid(
+	git_oid *out, git_repository *repo, const char *name)
+{
+	int error;
+	git_reference *ref;
+
+	if ((error = git_reference_lookup_resolved(&ref, repo, name, -1)) < 0)
+		return error;
+
+	git_oid_cpy(out, git_reference_oid(ref));
+	git_reference_free(ref);
+	return 0;
+}
+
+int git_reference_lookup_resolved(
+	git_reference **ref_out,
+	git_repository *repo,
+	const char *name,
+	int max_nesting)
+{
+	git_reference *scan;
+	int result, nesting;
 
 	assert(ref_out && repo && name);
+
 	*ref_out = NULL;
 
-	if (normalize_name(normalized_name, sizeof(normalized_name), name, 0) < 0)
-		return -1;
+	if (max_nesting > MAX_NESTING_LEVEL)
+		max_nesting = MAX_NESTING_LEVEL;
+	else if (max_nesting < 0)
+		max_nesting = DEFAULT_NESTING_LEVEL;
 
-	if (reference_alloc(&ref, repo, normalized_name) < 0)
-		return -1;
+	scan = git__calloc(1, sizeof(git_reference));
+	GITERR_CHECK_ALLOC(scan);
 
-	result = reference_lookup(ref);
-	if (result == 0)
-		*ref_out = ref;
+	scan->name = git__calloc(GIT_REFNAME_MAX + 1, sizeof(char));
+	GITERR_CHECK_ALLOC(scan->name);
 
-	return result;
+	if ((result = normalize_name(scan->name, GIT_REFNAME_MAX, name, 0)) < 0) {
+		git_reference_free(scan);
+		return result;
+	}
+
+	scan->target.symbolic = git__strdup(scan->name);
+	GITERR_CHECK_ALLOC(scan->target.symbolic);
+
+	scan->owner = repo;
+	scan->flags = GIT_REF_SYMBOLIC;
+
+	for (nesting = max_nesting;
+		 nesting >= 0 && (scan->flags & GIT_REF_SYMBOLIC) != 0;
+		 nesting--)
+	{
+		if (nesting != max_nesting)
+			strncpy(scan->name, scan->target.symbolic, GIT_REFNAME_MAX);
+
+		scan->mtime = 0;
+
+		if ((result = reference_lookup(scan)) < 0)
+			return result; /* lookup git_reference_free on scan already */
+	}
+
+	if ((scan->flags & GIT_REF_OID) == 0 && max_nesting != 0) {
+		giterr_set(GITERR_REFERENCE,
+			"Cannot resolve reference (>%u levels deep)", max_nesting);
+		git_reference_free(scan);
+		return -1;
+	}
+
+	*ref_out = scan;
+	return 0;
 }
 
 /**
@@ -1381,47 +1438,10 @@ rollback:
 
 int git_reference_resolve(git_reference **ref_out, git_reference *ref)
 {
-	int result, i = 0;
-	git_repository *repo;
-
-	assert(ref);
-
-	*ref_out = NULL;
-	repo = ref->owner;
-
-	/* If the reference is already resolved, we need to return a
-	 * copy. Instead of duplicating `ref`, we look it up again to
-	 * ensure the copy is out to date */
 	if (ref->flags & GIT_REF_OID)
 		return git_reference_lookup(ref_out, ref->owner, ref->name);
-
-	/* Otherwise, keep iterating until the reference is resolved */
-	for (i = 0; i < MAX_NESTING_LEVEL; ++i) {
-		git_reference *new_ref;
-
-		result = git_reference_lookup(&new_ref, repo, ref->target.symbolic);
-		if (result < 0)
-			return result;
-
-		/* Free intermediate references, except for the original one
-		 * we've received */
-		if (i > 0)
-			git_reference_free(ref);
-
-		ref = new_ref;
-
-		/* When the reference we've just looked up is an OID, we've
-		 * successfully resolved the symbolic ref */
-		if (ref->flags & GIT_REF_OID) {
-			*ref_out = ref;
-			return 0;
-		}
-	}
-
-	giterr_set(GITERR_REFERENCE,
-		"Symbolic reference too nested (%d levels deep)", MAX_NESTING_LEVEL);
-
-	return -1;
+	else
+		return git_reference_lookup_resolved(ref_out, ref->owner, ref->target.symbolic, -1);
 }
 
 int git_reference_packall(git_repository *repo)
@@ -1649,3 +1669,20 @@ int git_reference__normalize_name_oid(
 {
 	return normalize_name(buffer_out, out_size, name, 1);
 }
+
+#define GIT_REF_TYPEMASK (GIT_REF_OID | GIT_REF_SYMBOLIC)
+
+int git_reference_cmp(git_reference *ref1, git_reference *ref2)
+{
+	assert(ref1 && ref2);
+
+	/* let's put symbolic refs before OIDs */
+	if ((ref1->flags & GIT_REF_TYPEMASK) != (ref2->flags & GIT_REF_TYPEMASK))
+		return (ref1->flags & GIT_REF_SYMBOLIC) ? -1 : 1;
+
+	if (ref1->flags & GIT_REF_SYMBOLIC)
+		return strcmp(ref1->target.symbolic, ref2->target.symbolic);
+
+	return git_oid_cmp(&ref1->target.oid, &ref2->target.oid);
+}
+

src/refs.h

@@ -55,4 +55,27 @@ void git_repository__refcache_free(git_refcache *refs);
 int git_reference__normalize_name(char *buffer_out, size_t out_size, const char *name);
 int git_reference__normalize_name_oid(char *buffer_out, size_t out_size, const char *name);
 
+/**
+ * Lookup a reference by name and try to resolve to an OID.
+ *
+ * You can control how many dereferences this will attempt to resolve the
+ * reference with the `max_deref` parameter, or pass -1 to use a sane
+ * default.  If you pass 0 for `max_deref`, this will not attempt to resolve
+ * the reference.  For any value of `max_deref` other than 0, not
+ * successfully resolving the reference will be reported as an error.
+
+ * 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
+ * @param name The long name for the reference (e.g. HEAD, ref/heads/master, refs/tags/v0.1.0, ...)
+ * @param max_deref Maximum number of dereferences to make of symbolic refs, 0 means simple lookup, < 0 means use default reasonable value
+ * @return 0 on success or < 0 on error; not being able to resolve the reference is an error unless 0 was passed for max_deref
+ */
+int git_reference_lookup_resolved(
+	git_reference **reference_out,
+	git_repository *repo,
+	const char *name,
+	int max_deref);
+
 #endif

src/repository.c

@@ -772,24 +772,7 @@ int git_repository_head_detached(git_repository *repo)
 
 int git_repository_head(git_reference **head_out, git_repository *repo)
 {
-	git_reference *ref, *resolved_ref;
-	int error;
-
-	*head_out = NULL;
-
-	error = git_reference_lookup(&ref, repo, GIT_HEAD_FILE);
-	if (error < 0)
-		return error;
-
-	error = git_reference_resolve(&resolved_ref, ref);
-	if (error < 0) {
-		git_reference_free(ref);
-		return error;
-	}
-
-	git_reference_free(ref);
-	*head_out = resolved_ref;
-	return 0;
+	return git_reference_lookup_resolved(head_out, repo, GIT_HEAD_FILE, -1);
 }
 
 int git_repository_head_orphan(git_repository *repo)

src/revwalk.c

@@ -492,21 +492,12 @@ int git_revwalk_hide(git_revwalk *walk, const git_oid *oid)
 
 static int push_ref(git_revwalk *walk, const char *refname, int hide)
 {
-	git_reference *ref, *resolved;
-	int error;
+	git_oid oid;
 
-	if (git_reference_lookup(&ref, walk->repo, refname) < 0)
+	if (git_reference_lookup_oid(&oid, walk->repo, refname) < 0)
 		return -1;
 
-	error = git_reference_resolve(&resolved, ref);
-	git_reference_free(ref);
-	if (error < 0)
-		return -1;
-
-	error = push_commit(walk, git_reference_oid(resolved), hide);
-	git_reference_free(resolved);
-
-	return error;
+	return push_commit(walk, &oid, hide);
 }
 
 struct push_cb_data {

src/status.c

@@ -20,31 +20,19 @@
 
 static int resolve_head_to_tree(git_tree **tree, git_repository *repo)
 {
-	git_reference *head = NULL;
+	git_oid head_oid;
 	git_object *obj = NULL;
 
-	if (git_reference_lookup(&head, repo, GIT_HEAD_FILE) < 0)
-		return -1;
-
-	if (git_reference_oid(head) == NULL) {
-		git_reference *resolved;
-
-		if (git_reference_resolve(&resolved, head) < 0) {
-			/* cannot resolve HEAD - probably brand new repo */
-			giterr_clear();
-			git_reference_free(head);
-			return GIT_ENOTFOUND;
-		}
-
-		git_reference_free(head);
-		head = resolved;
+	if (git_reference_lookup_oid(&head_oid, repo, GIT_HEAD_FILE) < 0) {
+		/* cannot resolve HEAD - probably brand new repo */
+		giterr_clear();
+		*tree = NULL;
+		return 0;
 	}
 
-	if (git_object_lookup(&obj, repo, git_reference_oid(head), GIT_OBJ_ANY) < 0)
+	if (git_object_lookup(&obj, repo, &head_oid, GIT_OBJ_ANY) < 0)
 		goto fail;
 
-	git_reference_free(head);
-
 	switch (git_object_type(obj)) {
 	case GIT_OBJ_TREE:
 		*tree = (git_tree *)obj;
@@ -62,7 +50,6 @@ static int resolve_head_to_tree(git_tree **tree, git_repository *repo)
 
 fail:
 	git_object_free(obj);
-	git_reference_free(head);
 	return -1;
 }
 
@@ -152,7 +139,7 @@ int git_status_foreach_ext(
 		diffopt.flags = diffopt.flags | GIT_DIFF_RECURSE_UNTRACKED_DIRS;
 	/* TODO: support EXCLUDE_SUBMODULES flag */
 
-	if (show != GIT_STATUS_SHOW_WORKDIR_ONLY &&
+	if (show != GIT_STATUS_SHOW_WORKDIR_ONLY && head != NULL &&
 		(err = git_diff_index_to_tree(repo, &diffopt, head, &idx2head)) < 0)
 		goto cleanup;
 

src/transports/local.c

@@ -26,31 +26,22 @@ static int add_ref(transport_local *t, const char *name)
 {
 	const char peeled[] = "^{}";
 	git_remote_head *head;
-	git_reference *ref = NULL, *resolved_ref = NULL;
 	git_object *obj = NULL, *target = NULL;
 	git_buf buf = GIT_BUF_INIT;
 
-	if (git_reference_lookup(&ref, t->repo, name) < 0)
-		return -1;
-
-	if (git_reference_resolve(&resolved_ref, ref) < 0) {
-		git_reference_free(ref);
-		return -1;
-	}
-
 	head = git__malloc(sizeof(git_remote_head));
 	GITERR_CHECK_ALLOC(head);
 
 	head->name = git__strdup(name);
 	GITERR_CHECK_ALLOC(head->name);
 
-	git_oid_cpy(&head->oid, git_reference_oid(resolved_ref));
-
-	if (git_vector_insert(&t->refs, head) < 0)
+	if (git_reference_lookup_oid(&head->oid, t->repo, name) < 0 ||
+		git_vector_insert(&t->refs, head) < 0)
+	{
+		git__free(head->name);
+		git__free(head);
 		return -1;
-
-	git_reference_free(ref);
-	git_reference_free(resolved_ref);
+	}
 
 	/* If it's not a tag, we don't need to try to peel it */
 	if (git__prefixcmp(name, GIT_REFS_TAGS_DIR))
@@ -100,10 +91,8 @@ static int store_refs(transport_local *t)
 
 	assert(t);
 
-	if (git_vector_init(&t->refs, ref_names.count, NULL) < 0)
-		return -1;
-
-	if (git_reference_listall(&ref_names, t->repo, GIT_REF_LISTALL) < 0)
+	if (git_reference_listall(&ref_names, t->repo, GIT_REF_LISTALL) < 0 ||
+		git_vector_init(&t->refs, (unsigned int)ref_names.count, NULL) < 0)
 		goto on_error;
 
 	/* Sort the references first */

tests-clar/refs/lookup.c

+#include "clar_libgit2.h"
+#include "refs.h"
+
+static git_repository *g_repo;
+
+void test_refs_lookup__initialize(void)
+{
+	g_repo = cl_git_sandbox_init("testrepo.git");
+}
+
+void test_refs_lookup__cleanup(void)
+{
+	cl_git_sandbox_cleanup();
+}
+
+void test_refs_lookup__with_resolve(void)
+{
+	git_reference *a, *b, *temp;
+
+	cl_git_pass(git_reference_lookup(&temp, g_repo, "HEAD"));
+	cl_git_pass(git_reference_resolve(&a, temp));
+	git_reference_free(temp);
+
+	cl_git_pass(git_reference_lookup_resolved(&b, g_repo, "HEAD", 5));
+	cl_assert(git_reference_cmp(a, b) == 0);
+	git_reference_free(b);
+
+	cl_git_pass(git_reference_lookup_resolved(&b, g_repo, "head-tracker", 5));
+	cl_assert(git_reference_cmp(a, b) == 0);
+	git_reference_free(b);
+
+	git_reference_free(a);
+}
+
+void test_refs_lookup__oid(void)
+{
+	git_oid tag, expected;
+
+	cl_git_pass(git_reference_lookup_oid(&tag, g_repo, "refs/tags/point_to_blob"));
+	cl_git_pass(git_oid_fromstr(&expected, "1385f264afb75a56a5bec74243be9b367ba4ca08"));
+	cl_assert(git_oid_cmp(&tag, &expected) == 0);
+}