branch: let branch filters imply --list

Currently, a branch filter like `--contains`, `--merged`, or
`--no-merged` is ignored when we are not in listing mode.
For example:

  git branch --contains=foo bar

will create the branch "bar" from the current HEAD, ignoring
the `--contains` argument entirely. This is not very
helpful. There are two reasonable behaviors for git here:

  1. Flag an error; the arguments do not make sense.

  2. Implicitly go into `--list` mode

This patch chooses the latter, as it is more convenient, and
there should not be any ambiguity with attempting to create
a branch; using `--contains` and not wanting to list is
nonsensical.

That leaves the case where an explicit modification option
like `-d` is given.  We already catch the case where
`--list` is given alongside `-d` and flag an error. With
this patch, we will also catch the use of `--contains` and
other filter options alongside `-d`.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-branch.txt

@@ -195,15 +195,15 @@ start-point is either a local or remote-tracking branch.
 
 --contains [<commit>]::
 	Only list branches which contain the specified commit (HEAD
-	if not specified).
+	if not specified). Implies `--list`.
 
 --merged [<commit>]::
 	Only list branches whose tips are reachable from the
-	specified commit (HEAD if not specified).
+	specified commit (HEAD if not specified). Implies `--list`.
 
 --no-merged [<commit>]::
 	Only list branches whose tips are not reachable from the
-	specified commit (HEAD if not specified).
+	specified commit (HEAD if not specified). Implies `--list`.
 
 <branchname>::
 	The name of the branch to create or delete.

builtin/branch.c

@@ -825,6 +825,9 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 	if (!delete && !rename && !edit_description && !new_upstream && !unset_upstream && argc == 0)
 		list = 1;
 
+	if (with_commit || merge_filter != NO_FILTER)
+		list = 1;
+
 	if (!!delete + !!rename + !!force_create + !!list + !!new_upstream + !!unset_upstream > 1)
 		usage_with_options(builtin_branch_usage, options);
 

t/t3201-branch-contains.sh

@@ -55,6 +55,16 @@ test_expect_success 'branch --contains=side' '
 
 '
 
+test_expect_success 'branch --contains with pattern implies --list' '
+
+	git branch --contains=master master >actual &&
+	{
+		echo "  master"
+	} >expect &&
+	test_cmp expect actual
+
+'
+
 test_expect_success 'side: branch --merged' '
 
 	git branch --merged >actual &&
@@ -66,6 +76,16 @@ test_expect_success 'side: branch --merged' '
 
 '
 
+test_expect_success 'branch --merged with pattern implies --list' '
+
+	git branch --merged=side master >actual &&
+	{
+		echo "  master"
+	} >expect &&
+	test_cmp expect actual
+
+'
+
 test_expect_success 'side: branch --no-merged' '
 
 	git branch --no-merged >actual &&
@@ -95,4 +115,19 @@ test_expect_success 'master: branch --no-merged' '
 
 '
 
+test_expect_success 'branch --no-merged with pattern implies --list' '
+
+	git branch --no-merged=master master >actual &&
+	>expect &&
+	test_cmp expect actual
+
+'
+
+test_expect_success 'implicit --list conflicts with modification options' '
+
+	test_must_fail git branch --contains=master -d &&
+	test_must_fail git branch --contains=master -m foo
+
+'
+
 test_done