branch: implement '--format' option

Implement the '--format' option provided by 'ref-filter'. This lets the
user list branches as per desired format similar to the implementation
in 'git for-each-ref'.

Add tests and documentation for the same.

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-branch.txt

@@ -12,7 +12,7 @@ SYNOPSIS
 	[--list] [-v [--abbrev=<length> | --no-abbrev]]
 	[--column[=<options>] | --no-column]
 	[(--merged | --no-merged | --contains) [<commit>]] [--sort=<key>]
-	[--points-at <object>] [<pattern>...]
+	[--points-at <object>] [--format=<format>] [<pattern>...]
 'git branch' [--set-upstream | --track | --no-track] [-l] [-f] <branchname> [<start-point>]
 'git branch' (--set-upstream-to=<upstream> | -u <upstream>) [<branchname>]
 'git branch' --unset-upstream [<branchname>]
@@ -250,6 +250,11 @@ start-point is either a local or remote-tracking branch.
 --points-at <object>::
 	Only list branches of the given object.
 
+--format <format>::
+	A string that interpolates `%(fieldname)` from the object
+	pointed at by a ref being shown.  The format is the same as
+	that of linkgit:git-for-each-ref[1].
+
 Examples
 --------
 

builtin/branch.c

@@ -28,6 +28,7 @@ static const char * const builtin_branch_usage[] = {
 	N_("git branch [<options>] [-r] (-d | -D) <branch-name>..."),
 	N_("git branch [<options>] (-m | -M) [<old-branch>] <new-branch>"),
 	N_("git branch [<options>] [-r | -a] [--points-at]"),
+	N_("git branch [<options>] [-r | -a] [--format]"),
 	NULL
 };
 
@@ -364,14 +365,14 @@ static char *build_format(struct ref_filter *filter, int maxwidth, const char *r
 	return strbuf_detach(&fmt, NULL);
 }
 
-static void print_ref_list(struct ref_filter *filter, struct ref_sorting *sorting)
+static void print_ref_list(struct ref_filter *filter, struct ref_sorting *sorting, const char *format)
 {
 	int i;
 	struct ref_array array;
 	int maxwidth = 0;
 	const char *remote_prefix = "";
 	struct strbuf out = STRBUF_INIT;
-	char *format;
+	char *to_free = NULL;
 
 	/*
 	 * If we are listing more than just remote branches,
@@ -388,7 +389,8 @@ static void print_ref_list(struct ref_filter *filter, struct ref_sorting *sortin
 	if (filter->verbose)
 		maxwidth = calc_maxwidth(&array, strlen(remote_prefix));
 
-	format = build_format(filter, maxwidth, remote_prefix);
+	if (!format)
+		format = to_free = build_format(filter, maxwidth, remote_prefix);
 	verify_ref_format(format);
 
 	ref_array_sort(sorting, &array);
@@ -407,7 +409,7 @@ static void print_ref_list(struct ref_filter *filter, struct ref_sorting *sortin
 	}
 
 	ref_array_clear(&array);
-	free(format);
+	free(to_free);
 }
 
 static void reject_rebase_or_bisect_branch(const char *target)
@@ -528,6 +530,7 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 	struct ref_filter filter;
 	int icase = 0;
 	static struct ref_sorting *sorting = NULL, **sorting_tail = &sorting;
+	const char *format = NULL;
 
 	struct option options[] = {
 		OPT_GROUP(N_("Generic options")),
@@ -569,6 +572,7 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 			N_("print only branches of the object"), 0, parse_opt_object_name
 		},
 		OPT_BOOL('i', "ignore-case", &icase, N_("sorting and filtering are case insensitive")),
+		OPT_STRING(  0 , "format", &format, N_("format"), N_("format to use for the output")),
 		OPT_END(),
 	};
 
@@ -641,7 +645,7 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		if (!sorting)
 			sorting = ref_default_sorting();
 		sorting->ignore_case = icase;
-		print_ref_list(&filter, sorting);
+		print_ref_list(&filter, sorting, format);
 		print_columns(&output, colopts, NULL);
 		string_list_clear(&output, 0);
 		return 0;

t/t3203-branch-output.sh

@@ -225,4 +225,18 @@ test_expect_success 'sort branches, ignore case' '
 	)
 '
 
+test_expect_success 'git branch --format option' '
+	cat >expect <<-\EOF &&
+	Refname is (HEAD detached from fromtag)
+	Refname is refs/heads/ambiguous
+	Refname is refs/heads/branch-one
+	Refname is refs/heads/branch-two
+	Refname is refs/heads/master
+	Refname is refs/heads/ref-to-branch
+	Refname is refs/heads/ref-to-remote
+	EOF
+	git branch --format="Refname is %(refname)" >actual &&
+	test_cmp expect actual
+'
+
 test_done