[PATCH v3] 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 x y' command that does not
exactly say which remote they want to work with, and there is no local
branch named y, we try to guess which remote by passing y then create
a new branch named y which tracks the remote branch.

If there are multiple remotes that have branch named y, we silently
gave up, leaving the variable branch intact.  This later causes
creating local branch and worktree not happen, and we end up with
passing an non-existing branch to lookup_commit_reference_by_name(),
triggering "invalid reference" error and die.

To resolve this issue, display a hint and a descriptive error message
and die immediately when multiple mathing branches are found.

Signed-off-by: Yoichi NAKAYAMA <yoichi.nakayama@gmail.com>
---
    worktree add: improve message for ambiguous remote branch name

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2197%2Fyoichi%2Fimprove-worktree-add-error-message-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2197/yoichi/improve-worktree-add-error-message-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/2197

Range-diff vs v2:

 1:  1bc57ce497 ! 1:  1b9364da7e worktree add: improve message for ambiguous remote branch name
     @@ Metadata
       ## Commit message ##
          worktree add: improve message for ambiguous remote branch name
      
     -    Display a hint and a descriptive error message when DWIM fails.
     +    When the user runs 'git worktree add x y' command that does not
     +    exactly say which remote they want to work with, and there is no local
     +    branch named y, we try to guess which remote by passing y then create
     +    a new branch named y which tracks the remote branch.
     +
     +    If there are multiple remotes that have branch named y, we silently
     +    gave up, leaving the variable branch intact.  This later causes
     +    creating local branch and worktree not happen, and we end up with
     +    passing an non-existing branch to lookup_commit_reference_by_name(),
     +    triggering "invalid reference" error and die.
     +
     +    To resolve this issue, display a hint and a descriptive error message
     +    and die immediately when multiple mathing branches are found.
      
          Signed-off-by: Yoichi NAKAYAMA <yoichi.nakayama@gmail.com>
      


 builtin/worktree.c      | 23 ++++++++++++++++++++++-
 t/t2400-worktree-add.sh |  4 ++--
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..b29c3a3755 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -64,6 +64,19 @@
 	"\n" \
 	"    git worktree add --orphan %s\n")
 
+#define WORKTREE_ADD_AMBIGUOUS_REMOTE_BRANCH_NAME_HINT_TEXT \
+	_("Matched multiple remote tracking branches, you can list them by:\n" \
+	"\n" \
+	"    git branch -r --list \"*/%s\"\n" \
+	"\n" \
+	"If you meant to create a worktree from a remote tracking branch on,\n" \
+	"e.g. 'origin', you can do so by:\n" \
+	"\n" \
+	"    git worktree add -b %s %s origin/%s\n" \
+	"\n" \
+	"If you'd like to always prefer some remote, e.g. 'origin',\n" \
+	"consider setting checkout.defaultRemote=origin in your config.")
+
 static const char * const git_worktree_usage[] = {
 	BUILTIN_WORKTREE_ADD_USAGE,
 	BUILTIN_WORKTREE_LIST_USAGE,
@@ -904,10 +917,18 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			int num_matches = 0;
+			remote = unique_tracking_name(branch, &oid, &num_matches);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet)
+					advise_if_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME,
+							  WORKTREE_ADD_AMBIGUOUS_REMOTE_BRANCH_NAME_HINT_TEXT,
+							  branch, branch, path, branch);
+				die(_("'%s' matched multiple (%d) remote tracking branches"),
+				    branch, num_matches);
 			}
 		}
 
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

base-commit: 010afd3166ddc64c9863b1506f12cbcdda0d4ea1
-- 
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