Merge branch 'sp/describe'

* sp/describe:
  Use git-describe --exact-match in bash prompt on detached HEAD
  Teach git-describe --exact-match to avoid expensive tag searches
  Avoid accessing non-tag refs in git-describe unless --all is requested
  Teach git-describe to use peeled ref information when scanning tags
  Optimize peel_ref for the current ref of a for_each_ref callback

Documentation/git-describe.txt

@@ -45,6 +45,11 @@ OPTIONS
 	candidates to describe the input committish consider
 	up to <n> candidates.  Increasing <n> above 10 will take
 	slightly longer but may produce a more accurate result.
+	An <n> of 0 will cause only exact matches to be output.
+
+--exact-match::
+	Only output exact matches (a tag directly references the
+	supplied commit).  This is a synonym for --candidates=0.
 
 --debug::
 	Verbosely display information about the searching strategy

builtin-describe.c

@@ -46,19 +46,34 @@ static void add_to_known_names(const char *path,
 
 static int get_name(const char *path, const unsigned char *sha1, int flag, void *cb_data)
 {
-	struct commit *commit = lookup_commit_reference_gently(sha1, 1);
+	int might_be_tag = !prefixcmp(path, "refs/tags/");
+	struct commit *commit;
 	struct object *object;
-	int prio;
+	unsigned char peeled[20];
+	int is_tag, prio;
 
-	if (!commit)
+	if (!all && !might_be_tag)
 		return 0;
-	object = parse_object(sha1);
+
+	if (!peel_ref(path, peeled) && !is_null_sha1(peeled)) {
+		commit = lookup_commit_reference_gently(peeled, 1);
+		if (!commit)
+			return 0;
+		is_tag = !!hashcmp(sha1, commit->object.sha1);
+	} else {
+		commit = lookup_commit_reference_gently(sha1, 1);
+		object = parse_object(sha1);
+		if (!commit || !object)
+			return 0;
+		is_tag = object->type == OBJ_TAG;
+	}
+
 	/* If --all, then any refs are used.
 	 * If --tags, then any tags are used.
 	 * Otherwise only annotated tags are used.
 	 */
-	if (!prefixcmp(path, "refs/tags/")) {
-		if (object->type == OBJ_TAG) {
+	if (might_be_tag) {
+		if (is_tag) {
 			prio = 2;
 			if (pattern && fnmatch(pattern, path + 10, 0))
 				prio = 0;
@@ -159,6 +174,8 @@ static void describe(const char *arg, int last_one)
 		return;
 	}
 
+	if (!max_candidates)
+		die("no tag exactly matches '%s'", sha1_to_hex(cmit->object.sha1));
 	if (debug)
 		fprintf(stderr, "searching to describe %s\n", arg);
 
@@ -255,6 +272,8 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
 		OPT_BOOLEAN(0, "all",        &all, "use any ref in .git/refs"),
 		OPT_BOOLEAN(0, "tags",       &tags, "use any tag in .git/refs/tags"),
 		OPT__ABBREV(&abbrev),
+		OPT_SET_INT(0, "exact-match", &max_candidates,
+			    "only output exact matches", 0),
 		OPT_INTEGER(0, "candidates", &max_candidates,
 			    "consider <n> most recent tags (default: 10)"),
 		OPT_STRING(0, "match",       &pattern, "pattern",
@@ -263,8 +282,8 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
 	};
 
 	argc = parse_options(argc, argv, options, describe_usage, 0);
-	if (max_candidates < 1)
-		max_candidates = 1;
+	if (max_candidates < 0)
+		max_candidates = 0;
 	else if (max_candidates > MAX_TAGS)
 		max_candidates = MAX_TAGS;
 

contrib/completion/git-completion.bash

@@ -91,7 +91,10 @@ __git_ps1 ()
 			fi
 			if ! b="$(git symbolic-ref HEAD 2>/dev/null)"
 			then
-				b="$(cut -c1-7 $g/HEAD)..."
+				if ! b="$(git describe --exact-match HEAD 2>/dev/null)"
+				then
+					b="$(cut -c1-7 $g/HEAD)..."
+				fi
 			fi
 		fi
 

refs.c

@@ -157,6 +157,7 @@ static struct cached_refs {
 	struct ref_list *loose;
 	struct ref_list *packed;
 } cached_refs;
+static struct ref_list *current_ref;
 
 static void free_ref_list(struct ref_list *list)
 {
@@ -476,6 +477,7 @@ static int do_one_ref(const char *base, each_ref_fn fn, int trim,
 		error("%s does not point to a valid object!", entry->name);
 		return 0;
 	}
+	current_ref = entry;
 	return fn(entry->name + trim, entry->sha1, entry->flag, cb_data);
 }
 
@@ -485,6 +487,16 @@ int peel_ref(const char *ref, unsigned char *sha1)
 	unsigned char base[20];
 	struct object *o;
 
+	if (current_ref && (current_ref->name == ref
+		|| !strcmp(current_ref->name, ref))) {
+		if (current_ref->flag & REF_KNOWS_PEELED) {
+			hashcpy(sha1, current_ref->peeled);
+			return 0;
+		}
+		hashcpy(base, current_ref->sha1);
+		goto fallback;
+	}
+
 	if (!resolve_ref(ref, base, 1, &flag))
 		return -1;
 
@@ -504,7 +516,7 @@ int peel_ref(const char *ref, unsigned char *sha1)
 		}
 	}
 
-	/* fallback - callers should not call this for unpacked refs */
+fallback:
 	o = parse_object(base);
 	if (o && o->type == OBJ_TAG) {
 		o = deref_tag(o, ref, 0);
@@ -519,7 +531,7 @@ int peel_ref(const char *ref, unsigned char *sha1)
 static int do_for_each_ref(const char *base, each_ref_fn fn, int trim,
 			   void *cb_data)
 {
-	int retval;
+	int retval = 0;
 	struct ref_list *packed = get_packed_refs();
 	struct ref_list *loose = get_loose_refs();
 
@@ -539,15 +551,18 @@ static int do_for_each_ref(const char *base, each_ref_fn fn, int trim,
 		}
 		retval = do_one_ref(base, fn, trim, cb_data, entry);
 		if (retval)
-			return retval;
+			goto end_each;
 	}
 
 	for (packed = packed ? packed : loose; packed; packed = packed->next) {
 		retval = do_one_ref(base, fn, trim, cb_data, packed);
 		if (retval)
-			return retval;
+			goto end_each;
 	}
-	return 0;
+
+end_each:
+	current_ref = NULL;
+	return retval;
 }
 
 int head_ref(each_ref_fn fn, void *cb_data)