worktree: add --guess-remote flag to add subcommand

Currently 'git worktree add <path>' creates a new branch named after the
basename of the <path>, that matches the HEAD of whichever worktree we
were on when calling "git worktree add <path>".

It's sometimes useful to have 'git worktree add <path> behave more like
the dwim machinery in 'git checkout <new-branch>', i.e. check if the new
branch name, derived from the basename of the <path>, uniquely matches
the branch name of a remote-tracking branch, and if so check out that
branch and set the upstream to the remote-tracking branch.

Add a new --guess-remote option that enables exactly that behaviour.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-worktree.txt

@@ -115,6 +115,13 @@ OPTIONS
 	such as configuring sparse-checkout. See "Sparse checkout"
 	in linkgit:git-read-tree[1].
 
+--[no-]guess-remote::
+	With `worktree add <path>`, without `<commit-ish>`, instead
+	of creating a new branch from HEAD, if there exists a tracking
+	branch in exactly one remote matching the basename of `<path>,
+	base the new branch on the remote-tracking branch, and mark
+	the remote-tracking branch as "upstream" from the new branch.
+
 --[no-]track::
 	When creating a new branch, if `<commit-ish>` is a branch,
 	mark it as "upstream" from the new branch.  This is the

builtin/worktree.c

@@ -343,6 +343,7 @@ static int add(int ac, const char **av, const char *prefix)
 	char *path;
 	const char *branch;
 	const char *opt_track = NULL;
+	int guess_remote = 0;
 	struct option options[] = {
 		OPT__FORCE(&opts.force, N_("checkout <branch> even if already checked out in other worktree")),
 		OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
@@ -355,6 +356,8 @@ static int add(int ac, const char **av, const char *prefix)
 		OPT_PASSTHRU(0, "track", &opt_track, NULL,
 			     N_("set up tracking mode (see git-branch(1))"),
 			     PARSE_OPT_NOARG | PARSE_OPT_OPTARG),
+		OPT_BOOL(0, "guess-remote", &guess_remote,
+			 N_("try to match the new branch name with a remote-tracking branch")),
 		OPT_END()
 	};
 
@@ -389,6 +392,13 @@ static int add(int ac, const char **av, const char *prefix)
 		int n;
 		const char *s = worktree_basename(path, &n);
 		opts.new_branch = xstrndup(s, n);
+		if (guess_remote) {
+			struct object_id oid;
+			const char *remote =
+				unique_tracking_name(opts.new_branch, &oid);
+			if (remote)
+				branch = remote;
+		}
 	}
 
 	if (ac == 2 && !opts.new_branch && !opts.detach) {

t/t2025-worktree-add.sh

@@ -384,4 +384,33 @@ test_expect_success '"add" <path> <branch> dwims' '
 	)
 '
 
+test_expect_success 'git worktree add does not match remote' '
+	test_when_finished rm -rf repo_a repo_b foo &&
+	setup_remote_repo repo_a repo_b &&
+	(
+		cd repo_b &&
+		git worktree add ../foo
+	) &&
+	(
+		cd foo &&
+		test_must_fail git config "branch.foo.remote" &&
+		test_must_fail git config "branch.foo.merge" &&
+		! test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
+	)
+'
+
+test_expect_success 'git worktree add --guess-remote sets up tracking' '
+	test_when_finished rm -rf repo_a repo_b foo &&
+	setup_remote_repo repo_a repo_b &&
+	(
+		cd repo_b &&
+		git worktree add --guess-remote ../foo
+	) &&
+	(
+		cd foo &&
+		test_branch_upstream foo repo_a foo &&
+		test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
+	)
+'
+
 test_done