[PATCH v5 1/5] branch: add --forked <remote>

["Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com>]

From: Harald Nordgren <haraldnordgren@gmail.com>

List local branches whose configured upstream falls within any of
the given <remote> arguments. <remote> may be either a configured
remote name (matching all of its remote-tracking branches) or a
single remote-tracking branch. Multiple <remote> arguments are
unioned.

This is the building block for --prune-merged, which deletes the
listed branches.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-branch.adoc |  12 ++++
 builtin/branch.c              | 110 +++++++++++++++++++++++++++++++++-
 t/t3200-branch.sh             |  54 +++++++++++++++++
 3 files changed, 174 insertions(+), 2 deletions(-)

diff --git a/Documentation/git-branch.adoc b/Documentation/git-branch.adoc
index c0afddc424..5773104cd3 100644
--- a/Documentation/git-branch.adoc
+++ b/Documentation/git-branch.adoc
@@ -24,6 +24,7 @@ git branch (-m|-M) [<old-branch>] <new-branch>
 git branch (-c|-C) [<old-branch>] <new-branch>
 git branch (-d|-D) [-r] <branch-name>...
 git branch --edit-description [<branch-name>]
+git branch --forked <remote>...
 
 DESCRIPTION
 -----------
@@ -199,6 +200,17 @@ This option is only applicable in non-verbose mode.
 	Print the name of the current branch. In detached `HEAD` state,
 	nothing is printed.
 
+`--forked`::
+	List local branches that fork from any of the given _<remote>_
+	arguments, that is, those whose configured upstream
+	(`branch.<name>.merge`) is one of those remotes' remote-tracking
+	branches.
++
+Each _<remote>_ may be either the name of a configured remote
+(e.g. `origin`, meaning any branch tracking a
+`refs/remotes/origin/*` ref) or a specific remote-tracking branch
+(e.g. `origin/master`). Multiple _<remote>_ arguments are unioned.
+
 `-v`::
 `-vv`::
 `--verbose`::
diff --git a/builtin/branch.c b/builtin/branch.c
index 1572a4f9ef..b3289a8875 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -38,6 +38,7 @@ static const char * const builtin_branch_usage[] = {
 	N_("git branch [<options>] (-c | -C) [<old-branch>] <new-branch>"),
 	N_("git branch [<options>] [-r | -a] [--points-at]"),
 	N_("git branch [<options>] [-r | -a] [--format]"),
+	N_("git branch [<options>] --forked <remote>..."),
 	NULL
 };
 
@@ -673,6 +674,105 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 	free_worktrees(worktrees);
 }
 
+static void parse_forked_args(int argc, const char **argv,
+			      struct string_list *remote_names,
+			      struct string_list *tracking_refs)
+{
+	int i;
+
+	for (i = 0; i < argc; i++) {
+		const char *arg = argv[i];
+		struct remote *remote;
+		struct object_id oid;
+		char *full_ref = NULL;
+
+		remote = remote_get(arg);
+		if (remote && remote_is_configured(remote, 0)) {
+			string_list_insert(remote_names, remote->name);
+			continue;
+		}
+
+		if (repo_dwim_ref(the_repository, arg, strlen(arg), &oid,
+				  &full_ref, 0) == 1 &&
+		    starts_with(full_ref, "refs/remotes/")) {
+			string_list_insert(tracking_refs, full_ref);
+			free(full_ref);
+			continue;
+		}
+		free(full_ref);
+
+		die(_("'%s' is neither a configured remote nor a "
+		      "remote-tracking branch"), arg);
+	}
+}
+
+static int branch_is_forked(const char *short_name,
+			    const struct string_list *remote_names,
+			    const struct string_list *tracking_refs)
+{
+	struct branch *branch = branch_get(short_name);
+	const char *upstream;
+
+	if (!branch || !branch->remote_name)
+		return 0;
+
+	if (string_list_has_string(remote_names, branch->remote_name))
+		return 1;
+
+	upstream = branch_get_upstream(branch, NULL);
+	if (upstream && string_list_has_string(tracking_refs, upstream))
+		return 1;
+
+	return 0;
+}
+
+struct forked_cb {
+	const struct string_list *remote_names;
+	const struct string_list *tracking_refs;
+	struct string_list *out;
+};
+
+static int collect_forked_branch(const struct reference *ref, void *cb_data)
+{
+	struct forked_cb *cb = cb_data;
+
+	if (ref->flags & REF_ISSYMREF)
+		return 0;
+	if (branch_is_forked(ref->name, cb->remote_names, cb->tracking_refs))
+		string_list_append(cb->out, ref->name);
+	return 0;
+}
+
+static int list_forked_branches(int argc, const char **argv)
+{
+	struct string_list remote_names = STRING_LIST_INIT_NODUP;
+	struct string_list tracking_refs = STRING_LIST_INIT_DUP;
+	struct string_list out = STRING_LIST_INIT_DUP;
+	struct string_list_item *item;
+	struct forked_cb cb = {
+		.remote_names = &remote_names,
+		.tracking_refs = &tracking_refs,
+		.out = &out,
+	};
+
+	if (!argc)
+		die(_("--forked requires at least one <remote>"));
+
+	parse_forked_args(argc, argv, &remote_names, &tracking_refs);
+
+	refs_for_each_branch_ref(get_main_ref_store(the_repository),
+				 collect_forked_branch, &cb);
+
+	string_list_sort(&out);
+	for_each_string_list_item(item, &out)
+		puts(item->string);
+
+	string_list_clear(&remote_names, 0);
+	string_list_clear(&tracking_refs, 0);
+	string_list_clear(&out, 0);
+	return 0;
+}
+
 static GIT_PATH_FUNC(edit_description, "EDIT_DESCRIPTION")
 
 static int edit_branch_description(const char *branch_name)
@@ -714,6 +814,7 @@ int cmd_branch(int argc,
 	/* possible actions */
 	int delete = 0, rename = 0, copy = 0, list = 0,
 	    unset_upstream = 0, show_current = 0, edit_description = 0;
+	int forked = 0;
 	const char *new_upstream = NULL;
 	int noncreate_actions = 0;
 	/* possible options */
@@ -767,6 +868,8 @@ int cmd_branch(int argc,
 		OPT_BOOL(0, "create-reflog", &reflog, N_("create the branch's reflog")),
 		OPT_BOOL(0, "edit-description", &edit_description,
 			 N_("edit the description for the branch")),
+		OPT_BOOL(0, "forked", &forked,
+			N_("list local branches forked from the given <remote>s")),
 		OPT__FORCE(&force, N_("force creation, move/rename, deletion"), PARSE_OPT_NOCOMPLETE),
 		OPT_MERGED(&filter, N_("print only branches that are merged")),
 		OPT_NO_MERGED(&filter, N_("print only branches that are not merged")),
@@ -811,7 +914,7 @@ int cmd_branch(int argc,
 			     0);
 
 	if (!delete && !rename && !copy && !edit_description && !new_upstream &&
-	    !show_current && !unset_upstream && argc == 0)
+	    !show_current && !unset_upstream && !forked && argc == 0)
 		list = 1;
 
 	if (filter.with_commit || filter.no_commit ||
@@ -820,7 +923,7 @@ int cmd_branch(int argc,
 
 	noncreate_actions = !!delete + !!rename + !!copy + !!new_upstream +
 			    !!show_current + !!list + !!edit_description +
-			    !!unset_upstream;
+			    !!unset_upstream + !!forked;
 	if (noncreate_actions > 1)
 		usage_with_options(builtin_branch_usage, options);
 
@@ -860,6 +963,9 @@ int cmd_branch(int argc,
 			die(_("branch name required"));
 		ret = delete_branches(argc, argv, delete > 1, filter.kind, quiet);
 		goto out;
+	} else if (forked) {
+		ret = list_forked_branches(argc, argv);
+		goto out;
 	} else if (show_current) {
 		print_current_branch_name();
 		ret = 0;
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index e7829c2c4b..24a3ec44ee 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -1717,4 +1717,58 @@ test_expect_success 'errors if given a bad branch name' '
 	test_cmp expect actual
 '
 
+test_expect_success '--forked: setup' '
+	test_create_repo forked-upstream &&
+	test_commit -C forked-upstream base &&
+	git -C forked-upstream branch one base &&
+	git -C forked-upstream branch two base &&
+
+	test_create_repo forked-other &&
+	test_commit -C forked-other other-base &&
+	git -C forked-other branch foreign other-base &&
+
+	git clone forked-upstream forked &&
+	git -C forked remote add other ../forked-other &&
+	git -C forked fetch other &&
+	git -C forked branch --track local-one origin/one &&
+	git -C forked branch --track local-two origin/two &&
+	git -C forked branch --track local-foreign other/foreign &&
+	git -C forked branch detached
+'
+
+test_expect_success '--forked <remote-name> lists branches tracking that remote' '
+	git -C forked branch --forked origin >actual &&
+	cat >expect <<-\EOF &&
+	local-one
+	local-two
+	main
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '--forked <remote-tracking-branch> lists only matching branches' '
+	git -C forked branch --forked origin/one >actual &&
+	echo local-one >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--forked unions multiple <remote> arguments' '
+	git -C forked branch --forked origin/one other >actual &&
+	cat >expect <<-\EOF &&
+	local-foreign
+	local-one
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '--forked rejects unknown remote/ref' '
+	test_must_fail git -C forked branch --forked nope 2>err &&
+	test_grep "neither a configured remote nor a remote-tracking branch" err
+'
+
+test_expect_success '--forked requires at least one <remote>' '
+	test_must_fail git -C forked branch --forked 2>err &&
+	test_grep "at least one <remote>" err
+'
+
 test_done
-- 
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