show-branch: optionally use unique prefix as name.

git-show-branch acquires two new options. --sha1-name to name
commits using the unique prefix of their object names, and
--no-name to not to show names at all.

This was outlined in <7vk6gpyuyr.fsf@assigned-by-dhcp.cox.net>

Signed-off-by: Junio C Hamano <junkio@cox.net>

4 files changed, 82 insertions, 44 deletions

diff --git a/Documentation/git-show-branch.txt b/Documentation/git-show-branch.txt
index e0dce7ec1..c6c97b21c 100644
--- a/Documentation/git-show-branch.txt
+++ b/Documentation/git-show-branch.txt
@@ -7,7 +7,7 @@ git-show-branch - Show branches and their commits.
 
 SYNOPSIS
 --------
-'git-show-branch [--all] [--heads] [--tags] [--more=<n> | --list | --independent | --merge-base] <reference>...'
+'git-show-branch [--all] [--heads] [--tags] [--more=<n> | --list | --independent | --merge-base] [--no-name | --sha1-name] <reference>...'
 
 DESCRIPTION
 -----------
@@ -44,6 +44,15 @@ OPTIONS
 	Among the <reference>s given, display only the ones that
 	cannot be reached from any other <reference>.
 
+--no-name::
+	Do not show naming strings for each commit.
+
+--sha1-name::
+	Instead of naming the commits using the path to reach
+	them from heads (e.g. "master~2" to mean the grandparent
+	of "master"), name them with the unique prefix of their
+	object names.
+
 Note that --more, --list, --independent and --merge-base options
 are mutually exclusive.
 
@@ -88,21 +97,6 @@ whose commit message is "Add 'git show-branch'.  "fixes" branch
 adds one commit 'Introduce "reset type"'.  "mhf" branch has many
 other commits.
 
-When only one head is given, the output format changes slightly
-to conserve space.  The '+' sign to show which commit is
-reachable from which head and the first N lines to show the list
-of heads being displayed are both meaningless so they are
-omitted.  Also the label given to each commit does not repeat
-the name of the branch because it is obvious.
-
-------------------------------------------------
-$ git show-branch --more=4 master
-[master] Add 'git show-branch'.
-[~1] Add a new extended SHA1 syntax <name>~<num>
-[~2] Fix "git-diff A B"
-[~3] git-ls-files: generalized pathspecs
-[~4] Make "git-ls-files" work in subdirectories
-------------------------------------------------
 
 Author
 ------
diff --git a/cache.h b/cache.h
index 64cbcac5b..41cc22c1a 100644
--- a/cache.h
+++ b/cache.h
@@ -194,6 +194,7 @@ extern char *git_path(const char *fmt, ...) __attribute__((format (printf, 1, 2)
 extern char *sha1_file_name(const unsigned char *sha1);
 extern char *sha1_pack_name(const unsigned char *sha1);
 extern char *sha1_pack_index_name(const unsigned char *sha1);
+extern const char *find_unique_abbrev(const unsigned char *sha1, int);
 extern const unsigned char null_sha1[20];
 
 int git_mkstemp(char *path, size_t n, const char *template);
diff --git a/sha1_name.c b/sha1_name.c
index f64755fbc..4e9a05233 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -119,6 +119,9 @@ static int find_short_packed_object(int len, const unsigned char *match, unsigne
 	return found;
 }
 
+#define SHORT_NAME_NOT_FOUND (-1)
+#define SHORT_NAME_AMBIGUOUS (-2)
+
 static int find_unique_short_object(int len, char *canonical,
 				    unsigned char *res, unsigned char *sha1)
 {
@@ -128,23 +131,24 @@ static int find_unique_short_object(int len, char *canonical,
 	has_unpacked = find_short_object_filename(len, canonical, unpacked_sha1);
 	has_packed = find_short_packed_object(len, res, packed_sha1);
 	if (!has_unpacked && !has_packed)
-		return -1;
+		return SHORT_NAME_NOT_FOUND;
 	if (1 < has_unpacked || 1 < has_packed)
-		return error("short SHA1 %.*s is ambiguous.", len, canonical);
+		return SHORT_NAME_AMBIGUOUS;
 	if (has_unpacked != has_packed) {
 		memcpy(sha1, (has_packed ? packed_sha1 : unpacked_sha1), 20);
 		return 0;
 	}
 	/* Both have unique ones -- do they match? */
 	if (memcmp(packed_sha1, unpacked_sha1, 20))
-		return error("short SHA1 %.*s is ambiguous.", len, canonical);
+		return -2;
 	memcpy(sha1, packed_sha1, 20);
 	return 0;
 }
 
-static int get_short_sha1(const char *name, int len, unsigned char *sha1)
+static int get_short_sha1(const char *name, int len, unsigned char *sha1,
+			  int quietly)
 {
-	int i;
+	int i, status;
 	char canonical[40];
 	unsigned char res[20];
 
@@ -171,7 +175,29 @@ static int get_short_sha1(const char *name, int len, unsigned char *sha1)
 		res[i >> 1] |= val;
 	}
 
-	return find_unique_short_object(i, canonical, res, sha1);
+	status = find_unique_short_object(i, canonical, res, sha1);
+	if (!quietly && (status == SHORT_NAME_AMBIGUOUS))
+		return error("short SHA1 %.*s is ambiguous.", len, canonical);
+	return status;
+}
+
+const char *find_unique_abbrev(const unsigned char *sha1, int len)
+{
+	int status;
+	static char hex[41];
+	memcpy(hex, sha1_to_hex(sha1), 40);
+	while (len < 40) {
+		unsigned char sha1_ret[20];
+		status = get_short_sha1(hex, len, sha1_ret, 1);
+		if (!status) {
+			hex[len] = 0;
+			return hex;
+		}
+		if (status != SHORT_NAME_AMBIGUOUS)
+			return NULL;
+		len++;
+	}
+	return NULL;
 }
 
 static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
@@ -292,7 +318,7 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 	ret = get_sha1_basic(name, len, sha1);
 	if (!ret)
 		return 0;
-	return get_short_sha1(name, len, sha1);
+	return get_short_sha1(name, len, sha1, 0);
 }
 
 /*
diff --git a/show-branch.c b/show-branch.c
index 8429c171c..bb14c8677 100644
--- a/show-branch.c
+++ b/show-branch.c
@@ -133,25 +133,28 @@ static void name_commits(struct commit_list *list,
 			nth = 0;
 			while (parents) {
 				struct commit *p = parents->item;
-				char newname[1000];
+				char newname[1000], *en;
 				parents = parents->next;
 				nth++;
 				if (p->object.util)
 					continue;
+				en = newname;
 				switch (n->generation) {
 				case 0:
-					sprintf(newname, "%s^%d",
-						n->head_name, nth);
+					en += sprintf(en, "%s", n->head_name);
 					break;
 				case 1:
-					sprintf(newname, "%s^^%d",
-						n->head_name, nth);
+					en += sprintf(en, "%s^", n->head_name);
 					break;
 				default:
-					sprintf(newname, "%s~%d^%d",
-						n->head_name, n->generation,
-						nth);
+					en += sprintf(en, "%s~%d",
+						n->head_name, n->generation);
+					break;
 				}
+				if (nth == 1)
+					en += sprintf(en, "^");
+				else
+					en += sprintf(en, "^%d", nth);
 				name_commit(p, strdup(newname), 0);
 				i++;
 				name_first_parent_chain(p);
@@ -205,7 +208,7 @@ static void join_revs(struct commit_list **list_p,
 	}
 }
 
-static void show_one_commit(struct commit *commit)
+static void show_one_commit(struct commit *commit, int no_name)
 {
 	char pretty[128], *cp;
 	struct commit_name *name = commit->object.util;
@@ -218,11 +221,21 @@ static void show_one_commit(struct commit *commit)
 		cp = pretty + 8;
 	else
 		cp = pretty;
-	if (name && name->head_name) {
-		printf("[%s", name->head_name);
-		if (name->generation)
-			printf("~%d", name->generation);
-		printf("] ");
+
+	if (!no_name) {
+		if (name && name->head_name) {
+			printf("[%s", name->head_name);
+			if (name->generation) {
+				if (name->generation == 1)
+					printf("^");
+				else
+					printf("~%d", name->generation);
+			}
+			printf("] ");
+		}
+		else
+			printf("[%s] ",
+			       find_unique_abbrev(commit->object.sha1, 7));
 	}
 	puts(cp);
 }
@@ -354,7 +367,8 @@ int main(int ac, char **av)
 	unsigned char head_sha1[20];
 	int merge_base = 0;
 	int independent = 0;
-	char **label;
+	int no_name = 0;
+	int sha1_name = 0;
 
 	setup_git_directory();
 
@@ -370,6 +384,10 @@ int main(int ac, char **av)
 			extra = 1;
 		else if (!strcmp(arg, "--list"))
 			extra = -1;
+		else if (!strcmp(arg, "--no-name"))
+			no_name = 1;
+		else if (!strcmp(arg, "--sha1-name"))
+			sha1_name = 1;
 		else if (!strncmp(arg, "--more=", 7))
 			extra = atoi(arg + 7);
 		else if (!strcmp(arg, "--merge-base"))
@@ -465,7 +483,8 @@ int main(int ac, char **av)
 				printf("%c [%s] ",
 				       is_head ? '*' : '!', ref_name[i]);
 			}
-			show_one_commit(rev[i]);
+			/* header lines never need name */
+			show_one_commit(rev[i], 1);
 		}
 		if (0 <= extra) {
 			for (i = 0; i < num_rev; i++)
@@ -480,7 +499,8 @@ int main(int ac, char **av)
 	sort_in_topological_order(&seen);
 
 	/* Give names to commits */
-	name_commits(seen, rev, ref_name, num_rev);
+	if (!sha1_name && !no_name)
+		name_commits(seen, rev, ref_name, num_rev);
 
 	all_mask = ((1u << (REV_SHIFT + num_rev)) - 1);
 	all_revs = all_mask & ~((1u << REV_SHIFT) - 1);
@@ -490,7 +510,6 @@ int main(int ac, char **av)
 		struct commit *commit = pop_one_commit(&seen);
 		int this_flag = commit->object.flags;
 		int is_merge_point = (this_flag & all_revs) == all_revs;
-		static char *obvious[] = { "" };
 
 		if (is_merge_point)
 			shown_merge_point = 1;
@@ -501,9 +520,7 @@ int main(int ac, char **av)
 					? '+' : ' ');
 			putchar(' ');
 		}
-		show_one_commit(commit);
-		if (num_rev == 1)
-			label = obvious;
+		show_one_commit(commit, no_name);
 		if (shown_merge_point && is_merge_point)
 			if (--extra < 0)
 				break;