branch: add --unset-upstream option

We have ways of setting the upstream information, but if we want to
unset it, we need to resort to modifying the configuration manually.

Teach branch an --unset-upstream option that unsets this information.

Signed-off-by: Carlos Martín Nieto <cmn@elego.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-branch.txt

@@ -14,6 +14,7 @@ SYNOPSIS
 	[(--merged | --no-merged | --contains) [<commit>]] [<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>]
 'git branch' (-m | -M) [<oldbranch>] <newbranch>
 'git branch' (-d | -D) [-r] <branchname>...
 'git branch' --edit-description [<branchname>]
@@ -180,6 +181,10 @@ start-point is either a local or remote-tracking branch.
 	considered <branchname>'s upstream branch. If no <branchname>
 	is specified, then it defaults to the current branch.
 
+--unset-upstream::
+	Remove the upstream information for <branchname>. If no branch
+	is specified it defaults to the current branch.
+
 --edit-description::
 	Open an editor and edit the text to explain what the branch is
 	for, to be used by various other commands (e.g. `request-pull`).

builtin/branch.c

@@ -712,7 +712,7 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 	int delete = 0, rename = 0, force_create = 0, list = 0;
 	int verbose = 0, abbrev = -1, detached = 0;
 	int reflog = 0, edit_description = 0;
-	int quiet = 0;
+	int quiet = 0, unset_upstream = 0;
 	const char *new_upstream = NULL;
 	enum branch_track track;
 	int kinds = REF_LOCAL_BRANCH;
@@ -728,6 +728,7 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		OPT_SET_INT( 0, "set-upstream",  &track, "change upstream info",
 			BRANCH_TRACK_OVERRIDE),
 		OPT_STRING('u', "set-upstream-to", &new_upstream, "upstream", "change the upstream info"),
+		OPT_BOOLEAN(0, "unset-upstream", &unset_upstream, "Unset the upstream info"),
 		OPT__COLOR(&branch_use_color, "use colored output"),
 		OPT_SET_INT('r', "remotes",     &kinds, "act on remote-tracking branches",
 			REF_REMOTE_BRANCH),
@@ -796,10 +797,10 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix, options, builtin_branch_usage,
 			     0);
 
-	if (!delete && !rename && !edit_description && !new_upstream && argc == 0)
+	if (!delete && !rename && !edit_description && !new_upstream && !unset_upstream && argc == 0)
 		list = 1;
 
-	if (!!delete + !!rename + !!force_create + !!list + !!new_upstream > 1)
+	if (!!delete + !!rename + !!force_create + !!list + !!new_upstream + !!unset_upstream > 1)
 		usage_with_options(builtin_branch_usage, options);
 
 	if (abbrev == -1)
@@ -865,6 +866,20 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		 * info and making sure new_upstream is correct
 		 */
 		create_branch(head, branch->name, new_upstream, 0, 0, 0, quiet, BRANCH_TRACK_OVERRIDE);
+	} else if (unset_upstream) {
+		struct branch *branch = branch_get(argv[0]);
+		struct strbuf buf = STRBUF_INIT;
+
+		if (!branch_has_merge_config(branch)) {
+			die(_("Branch '%s' has no upstream information"), branch->name);
+		}
+
+		strbuf_addf(&buf, "branch.%s.remote", branch->name);
+		git_config_set_multivar(buf.buf, NULL, NULL, 1);
+		strbuf_reset(&buf);
+		strbuf_addf(&buf, "branch.%s.merge", branch->name);
+		git_config_set_multivar(buf.buf, NULL, NULL, 1);
+		strbuf_release(&buf);
 	} else if (argc > 0 && argc <= 2) {
 		if (kinds != REF_LOCAL_BRANCH)
 			die(_("-a and -r options to 'git branch' do not make sense with a branch name"));

t/t3200-branch.sh

@@ -383,6 +383,28 @@ test_expect_success 'use --set-upstream-to modify a particular branch' \
      test "$(git config branch.my13.remote)" = "." &&
      test "$(git config branch.my13.merge)" = "refs/heads/master"'
 
+test_expect_success '--unset-upstream should fail if given a non-existent branch' \
+    'test_must_fail git branch --unset-upstream i-dont-exist'
+
+test_expect_success 'test --unset-upstream on HEAD' \
+    'git branch my14
+     test_config branch.master.remote foo &&
+     test_config branch.master.merge foo &&
+     git branch --set-upstream-to my14 &&
+     git branch --unset-upstream &&
+     test_must_fail git config branch.master.remote &&
+     test_must_fail git config branch.master.merge &&
+     # fail for a branch without upstream set
+     test_must_fail git branch --unset-upstream
+'
+
+test_expect_success 'test --unset-upstream on a particular branch' \
+    'git branch my15
+     git branch --set-upstream-to master my14 &&
+     git branch --unset-upstream my14 &&
+     test_must_fail git config branch.my14.remote &&
+     test_must_fail git config branch.my14.merge'
+
 # Keep this test last, as it changes the current branch
 cat >expect <<EOF
 $_z40 $HEAD $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> 1117150200 +0000	branch: Created from master