git-branch: add support for --merged and --no-merged

These options filter the output from git branch to only include branches
whose tip is either merged or not merged into HEAD.

The use-case for these options is when working with integration of branches
from many remotes: `git branch --no-merged -a` will show a nice list of merge
candidates while `git branch --merged -a` will show the progress of your
integration work.

Also, a plain `git branch --merged` is a quick way to find local branches
which you might want to delete.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-branch.txt

@@ -8,7 +8,7 @@ git-branch - List, create, or delete branches
 SYNOPSIS
 --------
 [verse]
-'git-branch' [--color | --no-color] [-r | -a]
+'git-branch' [--color | --no-color] [-r | -a] [--merged | --no-merged]
 	   [-v [--abbrev=<length> | --no-abbrev]]
 	   [--contains <commit>]
 'git-branch' [--track | --no-track] [-l] [-f] <branchname> [<start-point>]
@@ -24,6 +24,8 @@ and option `-a` shows both.
 With `--contains <commit>`, shows only the branches that
 contains the named commit (in other words, the branches whose
 tip commits are descendant of the named commit).
+With `--merged`, only branches merged into HEAD will be listed, and
+with `--no-merged` only branches not merged into HEAD will be listed.
 
 In its second form, a new branch named <branchname> will be created.
 It will start out with a head equal to the one given as <start-point>.

builtin-branch.c

@@ -15,7 +15,7 @@
 #include "branch.h"
 
 static const char * const builtin_branch_usage[] = {
-	"git-branch [options] [-r | -a]",
+	"git-branch [options] [-r | -a] [--merged | --no-merged]",
 	"git-branch [options] [-l] [-f] <branchname> [<start-point>]",
 	"git-branch [options] [-r] (-d | -D) <branchname>",
 	"git-branch [options] (-m | -M) [<oldbranch>] <newbranch>",
@@ -46,6 +46,8 @@ enum color_branch {
 	COLOR_BRANCH_CURRENT = 4,
 };
 
+static int mergefilter = -1;
+
 static int parse_branch_color_slot(const char *var, int ofs)
 {
 	if (!strcasecmp(var+ofs, "plain"))
@@ -210,6 +212,7 @@ static int append_ref(const char *refname, const unsigned char *sha1, int flags,
 	struct ref_item *newitem;
 	int kind = REF_UNKNOWN_TYPE;
 	int len;
+	static struct commit_list branch;
 
 	/* Detect kind */
 	if (!prefixcmp(refname, "refs/heads/")) {
@@ -231,6 +234,16 @@ static int append_ref(const char *refname, const unsigned char *sha1, int flags,
 	if ((kind & ref_list->kinds) == 0)
 		return 0;
 
+	if (mergefilter > -1) {
+		branch.item = lookup_commit_reference_gently(sha1, 1);
+		if (!branch.item)
+			die("Unable to lookup tip of branch %s", refname);
+		if (mergefilter == 0 && has_commit(head_sha1, &branch))
+			return 0;
+		if (mergefilter == 1 && !has_commit(head_sha1, &branch))
+			return 0;
+	}
+
 	/* Resize buffer */
 	if (ref_list->index >= ref_list->alloc) {
 		ref_list->alloc = alloc_nr(ref_list->alloc);
@@ -444,6 +457,7 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		OPT_BIT('M', NULL, &rename, "move/rename a branch, even if target exists", 2),
 		OPT_BOOLEAN('l', NULL, &reflog, "create the branch's reflog"),
 		OPT_BOOLEAN('f', NULL, &force_create, "force creation (when already exists)"),
+		OPT_SET_INT(0, "merged", &mergefilter, "list only merged branches", 1),
 		OPT_END(),
 	};