[PATCH] Add 'git show-branch'.

The 'git show-branches' command turns out to be reasonably useful,
but painfully slow.  So rewrite it in C, using ideas from merge-base
while enhancing it a bit more.

 - Unlike show-branches, it can take --heads (show me all my
   heads), --tags (show me all my tags), or --all (both).

 - It can take --more=<number> to show beyond the merge-base.

 - It shows the short name for each commit in the extended SHA1
   syntax.

 - It can find merge-base for more than two heads.

Examples:

    $ git show-branch --more=6 HEAD

    is almost the same as "git log --pretty=oneline --max-count=6".

    $ git show-branch --merge-base master mhf misc

    finds the merge base of the three given heads.

    $ git show-branch master mhf misc

    shows logs from the top of these three branch heads, up to their
    common ancestor commit is shown.

    $ git show-branch --all --more=10

    is poor-man's gitk, showing all the tags and heads, and
    going back 10 commits beyond the merge base of those refs.

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

Makefile

@@ -84,7 +84,7 @@ PROG=   git-update-cache git-diff-files git-init-db git-write-tree \
 	git-diff-stages git-rev-parse git-patch-id git-pack-objects \
 	git-unpack-objects git-verify-pack git-receive-pack git-send-pack \
 	git-prune-packed git-fetch-pack git-upload-pack git-clone-pack \
-	git-show-index git-daemon git-var git-peek-remote \
+	git-show-index git-daemon git-var git-peek-remote git-show-branch \
 	git-update-server-info git-show-rev-cache git-build-rev-cache
 
 ifndef NO_CURL

commit.c

@@ -38,23 +38,32 @@ enum cmit_fmt get_commit_format(const char *arg)
 	die("invalid --pretty format");
 }
 
-static struct commit *check_commit(struct object *obj, const unsigned char *sha1)
+static struct commit *check_commit(struct object *obj,
+				   const unsigned char *sha1,
+				   int quiet)
 {
 	if (obj->type != commit_type) {
-		error("Object %s is a %s, not a commit", 
-		      sha1_to_hex(sha1), obj->type);
+		if (!quiet)
+			error("Object %s is a %s, not a commit",
+			      sha1_to_hex(sha1), obj->type);
 		return NULL;
 	}
 	return (struct commit *) obj;
 }
 
-struct commit *lookup_commit_reference(const unsigned char *sha1)
+struct commit *lookup_commit_reference_gently(const unsigned char *sha1,
+					      int quiet)
 {
 	struct object *obj = deref_tag(parse_object(sha1));
 
 	if (!obj)
 		return NULL;
-	return check_commit(obj, sha1);
+	return check_commit(obj, sha1, quiet);
+}
+
+struct commit *lookup_commit_reference(const unsigned char *sha1)
+{
+	return lookup_commit_reference_gently(sha1, 0);
 }
 
 struct commit *lookup_commit(const unsigned char *sha1)
@@ -69,7 +78,7 @@ struct commit *lookup_commit(const unsigned char *sha1)
 	}
 	if (!obj->type)
 		obj->type = commit_type;
-	return check_commit(obj, sha1);
+	return check_commit(obj, sha1, 0);
 }
 
 static unsigned long parse_commit_date(const char *buf)

commit.h

@@ -21,6 +21,8 @@ extern const char *commit_type;
 
 struct commit *lookup_commit(const unsigned char *sha1);
 struct commit *lookup_commit_reference(const unsigned char *sha1);
+struct commit *lookup_commit_reference_gently(const unsigned char *sha1,
+					      int quiet);
 
 int parse_commit_buffer(struct commit *item, void *buffer, unsigned long size);
 

show-branch.c

@@ -0,0 +1,325 @@
+#include <stdlib.h>
+#include "cache.h"
+#include "commit.h"
+#include "refs.h"
+
+static const char show_branch_usage[] =
+"git-show-branch [--all] [--heads] [--tags] [--more=count] [<refs>...]";
+
+#define UNINTERESTING	01
+
+#define REV_SHIFT	 2
+#define MAX_REVS	29 /* should not exceed bits_per_int - REV_SHIFT */
+
+static struct commit *interesting(struct commit_list *list)
+{
+	while (list) {
+		struct commit *commit = list->item;
+		list = list->next;
+		if (commit->object.flags & UNINTERESTING)
+			continue;
+		return commit;
+	}
+	return NULL;
+}
+
+static struct commit *pop_one_commit(struct commit_list **list_p)
+{
+	struct commit *commit;
+	struct commit_list *list;
+	list = *list_p;
+	commit = list->item;
+	*list_p = list->next;
+	free(list);
+	return commit;
+}
+
+struct commit_name {
+	int head_rev;	/* which head's ancestor? */
+	int generation;	/* how many parents away from head_rev */
+};
+
+/* Name the commit as nth generation ancestor of head_rev;
+ * we count only the first-parent relationship for naming purposes.
+ */
+static void name_commit(struct commit *commit, int head_rev, int nth)
+{
+	struct commit_name *name;
+	if (!commit->object.util)
+		commit->object.util = xmalloc(sizeof(struct commit_name));
+	name = commit->object.util;
+	name->head_rev = head_rev;
+	name->generation = nth;
+}
+
+/* Parent is the first parent of the commit.  We may name it
+ * as (n+1)th generation ancestor of the same head_rev as
+ * commit is nth generation ancestore of, if that generation
+ * number is better than the name it already has.
+ */
+static void name_parent(struct commit *commit, struct commit *parent)
+{
+	struct commit_name *commit_name = commit->object.util;
+	struct commit_name *parent_name = parent->object.util;
+	if (!commit_name)
+		return;
+	if (!parent_name ||
+	    commit_name->generation + 1 < parent_name->generation)
+		name_commit(parent, commit_name->head_rev,
+			    commit_name->generation + 1);
+}
+
+static int mark_seen(struct commit *commit, struct commit_list **seen_p)
+{
+	if (!commit->object.flags) {
+		insert_by_date(commit, seen_p);
+		return 1;
+	}
+	return 0;
+}
+
+static void join_revs(struct commit_list **list_p,
+		      struct commit_list **seen_p,
+		      int num_rev, int extra)
+{
+	int all_mask = ((1u << (REV_SHIFT + num_rev)) - 1);
+	int all_revs = all_mask & ~((1u << REV_SHIFT) - 1);
+
+	while (*list_p) {
+		struct commit_list *parents;
+		struct commit *commit = pop_one_commit(list_p);
+		int flags = commit->object.flags & all_mask;
+		int nth_parent = 0;
+		int still_interesting = !!interesting(*list_p);
+
+		if (!still_interesting && extra < 0)
+			break;
+
+		mark_seen(commit, seen_p);
+		if ((flags & all_revs) == all_revs)
+			flags |= UNINTERESTING;
+		parents = commit->parents;
+
+		while (parents) {
+			struct commit *p = parents->item;
+			int this_flag = p->object.flags;
+			parents = parents->next;
+			nth_parent++;
+			if (nth_parent == 1)
+				name_parent(commit, p);
+
+			if ((this_flag & flags) == flags)
+				continue;
+			parse_commit(p);
+			if (mark_seen(p, seen_p) && !still_interesting)
+				extra--;
+			p->object.flags |= flags;
+			insert_by_date(p, list_p);
+		}
+	}
+}
+
+static void show_one_commit(struct commit *commit, char **head_name)
+{
+	char pretty[128], *cp;
+	struct commit_name *name = commit->object.util;
+	pretty_print_commit(CMIT_FMT_ONELINE, commit->buffer, ~0,
+			    pretty, sizeof(pretty));
+	if (!strncmp(pretty, "[PATCH] ", 8))
+		cp = pretty + 8;
+	else
+		cp = pretty;
+	if (name && head_name) {
+		printf("[%s", head_name[name->head_rev]);
+		if (name->generation)
+			printf("~%d", name->generation);
+		printf("] ");
+	}
+	puts(cp);
+}
+
+static char *ref_name[MAX_REVS + 1];
+static int ref_name_cnt;
+
+static int append_ref(const char *refname, const unsigned char *sha1)
+{
+	struct commit *commit = lookup_commit_reference_gently(sha1, 1);
+	if (!commit)
+		return 0;
+	if (MAX_REVS < ref_name_cnt) {
+		fprintf(stderr, "warning: ignoring %s; "
+			"cannot handle more than %d refs",
+			refname, MAX_REVS);
+		return 0;
+	}
+	ref_name[ref_name_cnt++] = strdup(refname);
+	ref_name[ref_name_cnt] = NULL;
+	return 0;
+}
+
+static int append_head_ref(const char *refname, const unsigned char *sha1)
+{
+	if (strncmp(refname, "refs/heads/", 11))
+		return 0;
+	return append_ref(refname + 5, sha1);
+}
+
+static int append_tag_ref(const char *refname, const unsigned char *sha1)
+{
+	if (strncmp(refname, "refs/tags/", 10))
+		return 0;
+	return append_ref(refname + 5, sha1);
+}
+
+static void snarf_refs(int head, int tag)
+{
+	if (head)
+		for_each_ref(append_head_ref);
+	if (tag)
+		for_each_ref(append_tag_ref);
+}
+
+static int rev_is_head(char *head_path, int headlen,
+		       char *name,
+		       unsigned char *head_sha1, unsigned char *sha1)
+{
+	int namelen;
+	if ((!head_path[0]) || memcmp(head_sha1, sha1, 20))
+		return 0;
+	namelen = strlen(name);
+	if ((headlen < namelen) ||
+	    memcmp(head_path + headlen - namelen, name, namelen))
+		return 0;
+	if (headlen == namelen ||
+	    head_path[headlen - namelen - 1] == '/')
+		return 1;
+	return 0;
+}
+
+static int show_merge_base(struct commit_list *seen, int num_rev)
+{
+	int all_mask = ((1u << (REV_SHIFT + num_rev)) - 1);
+	int all_revs = all_mask & ~((1u << REV_SHIFT) - 1);
+
+	while (seen) {
+		struct commit *commit = pop_one_commit(&seen);
+		int flags = commit->object.flags & all_mask;
+		if (!(flags & UNINTERESTING) &&
+		    ((flags & all_revs) == all_revs)) {
+			puts(sha1_to_hex(commit->object.sha1));
+			return 0;
+		}
+	}
+	return 1;
+}
+
+int main(int ac, char **av)
+{
+	struct commit *rev[MAX_REVS], *commit;
+	struct commit_list *list = NULL, *seen = NULL;
+	int num_rev, i, extra = 0;
+	int all_heads = 0, all_tags = 0;
+	char head_path[128];
+	int head_path_len;
+	unsigned char head_sha1[20];
+	int merge_base = 0;
+
+	while (1 < ac && av[1][0] == '-') {
+		char *arg = av[1];
+		if (!strcmp(arg, "--all"))
+			all_heads = all_tags = 1;
+		else if (!strcmp(arg, "--heads"))
+			all_heads = 1;
+		else if (!strcmp(arg, "--tags"))
+			all_tags = 1;
+		else if (!strcmp(arg, "--more"))
+			extra = 1;
+		else if (!strncmp(arg, "--more=", 7)) {
+			extra = atoi(arg + 7);
+			if (extra < 0)
+				usage(show_branch_usage);
+		}
+		else if (!strcmp(arg, "--merge-base"))
+			merge_base = 1;
+		else
+			usage(show_branch_usage);
+		ac--; av++;
+	}
+	ac--; av++;
+
+	if (all_heads + all_tags)
+		snarf_refs(all_heads, all_tags);
+
+	while (0 < ac) {
+		unsigned char revkey[20];
+		if (get_sha1(*av, revkey))
+			die("bad sha1 reference %s", *av);
+		append_ref(*av, revkey);
+		ac--; av++;
+	}
+
+	/* If still no revs, then add heads */
+	if (!ref_name_cnt)
+		snarf_refs(1, 0);
+
+	for (num_rev = 0; ref_name[num_rev]; num_rev++) {
+		unsigned char revkey[20];
+
+		if (MAX_REVS <= num_rev)
+			die("cannot handle more than %d revs.", MAX_REVS);
+		if (get_sha1(ref_name[num_rev], revkey))
+			usage(show_branch_usage);
+		commit = lookup_commit_reference(revkey);
+		if (!commit)
+			die("cannot find commit %s (%s)",
+			    ref_name[num_rev], revkey);
+		parse_commit(commit);
+		if (!commit->object.util)
+			name_commit(commit, num_rev, 0);
+		mark_seen(commit, &seen);
+
+		/* rev#0 uses bit REV_SHIFT, rev#1 uses bit REV_SHIFT+1,
+		 * and so on.  REV_SHIFT bits from bit 0 are used for
+		 * internal bookkeeping.
+		 */
+		commit->object.flags |= 1u << (num_rev + REV_SHIFT);
+		insert_by_date(commit, &list);
+		rev[num_rev] = commit;
+	}
+	join_revs(&list, &seen, num_rev, extra);
+
+	head_path_len = readlink(".git/HEAD", head_path, sizeof(head_path)-1);
+	if ((head_path_len < 0) || get_sha1("HEAD", head_sha1))
+		head_path[0] = 0;
+	else
+		head_path[head_path_len] = 0;
+
+	if (merge_base)
+		return show_merge_base(seen, num_rev);
+
+	if (1 < num_rev)
+		for (i = 0; i < num_rev; i++) {
+			int j;
+			int is_head = rev_is_head(head_path,
+						  head_path_len,
+						  ref_name[i],
+						  head_sha1,
+						  rev[i]->object.sha1);
+			for (j = 0; j < i; j++)
+				putchar(' ');
+			printf("%c [%s] ", is_head ? '*' : '!', ref_name[i]);
+			show_one_commit(rev[i], NULL);
+		}
+	while (seen) {
+		struct commit *commit = pop_one_commit(&seen);
+		int this_flag = commit->object.flags;
+		if ((this_flag & UNINTERESTING) && (--extra < 0))
+			break;
+		for (i = 0; i < num_rev; i++)
+			putchar((this_flag & (1u << (i + REV_SHIFT)))
+				? '+' : ' ');
+		putchar(' ');
+		show_one_commit(commit, ref_name);
+	}
+	return 0;
+}