[PATCH v7 3/3] worktree add: improve message for ambiguous remote branch name

["Yoichi NAKAYAMA via GitGitGadget" <gitgitgadget@gmail.com>]

From: Yoichi NAKAYAMA <yoichi.nakayama@gmail.com>

When the user runs 'git worktree add ../foo-dir bar-topic' without
specifying a remote, and there is no local branch named bar-topic, we
try to guess which remote branch bar-topic refers to, then create a
new branch named bar-topic that tracks the remote branch.

If multiple remotes have a branch named bar-topic, we silently gave
up, leaving the variable 'branch' intact.  We then entered the
conditional clause 'if (!opts.orphan &&
!lookup_commit_reference_by_name(branch))' and triggered an "invalid
reference" error.  This error message did not provide enough
information to resolve the ambiguity.

When multiple matching branches are found, display a hint and a
descriptive error message and die immediately.

Signed-off-by: Yoichi NAKAYAMA <yoichi.nakayama@gmail.com>
---
 builtin/worktree.c      | 37 ++++++++++++++++++++++++++++++++++---
 t/t2400-worktree-add.sh |  4 ++--
 2 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 22c8e5e131..320b18873d 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -788,6 +788,25 @@ static char *dwim_branch(const char *path, char **new_branch)
 	return NULL;
 }
 
+static void advise_disambiguating_remotes(const char *path, const char *branch,
+					  const struct string_list *matched_remote_names)
+{
+	struct string_list_item *item;
+
+	advise(_("Branch name '%s' appears in multiple remotes:"), branch);
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to create a worktree from a remote tracking branch on\n"
+		 "<remote>, you can do so by:\n"
+		 "\n"
+		 "    git worktree add -b %s %s <remote>/%s\n"
+		 "\n"
+		 "If you'd like to always prefer some remote, e.g. 'origin',\n"
+		 "consider setting checkout.defaultRemote=origin in your config."),
+	       branch, path, branch);
+}
+
 static int add(int ac, const char **av, const char *prefix,
 	       struct repository *repo UNUSED)
 {
@@ -898,17 +917,29 @@ static int add(int ac, const char **av, const char *prefix,
 		/* DWIM: Infer --orphan when repo has no refs. */
 		opts.orphan = (!s) && dwim_orphan(&opts, !!opt_track, 1);
 	} else if (ac == 2) {
-		struct object_id oid;
 		struct commit *commit;
-		char *remote;
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL, NULL);
+			struct object_id oid;
+			char *remote;
+			int num_matches = 0;
+			struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+			remote = unique_tracking_name(branch, &oid, &num_matches,
+						      &matched_remote_names);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet &&
+				    advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+					advise_disambiguating_remotes(path, branch,
+								      &matched_remote_names);
+				die(_("'%s' matched multiple (%d) remote tracking branches"),
+				    branch, num_matches);
 			}
+			string_list_clear(&matched_remote_names, 0);
 		}
 
 		if (!strcmp(branch, "HEAD"))
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 87b926728a..5c105cf252 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -624,12 +624,12 @@ test_expect_success '"add" <path> <branch> dwims' '
 test_expect_success '"add" <path> <branch> dwims with checkout.defaultRemote' '
 	test_when_finished rm -rf repo_upstream repo_dwim foo &&
 	setup_remote_repo repo_upstream repo_dwim &&
-	git init repo_dwim &&
 	(
 		cd repo_dwim &&
 		git remote add repo_upstream2 ../repo_upstream &&
 		git fetch repo_upstream2 &&
-		test_must_fail git worktree add ../foo foo &&
+		test_must_fail git worktree add ../foo foo 2>error.actual &&
+		test_grep "matched multiple (2) remote tracking branches" error.actual &&
 		git -c checkout.defaultRemote=repo_upstream worktree add ../foo foo &&
 		git status -uno --porcelain >status.actual &&
 		test_must_be_empty status.actual
-- 
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