Merge branch 'tg/worktree-add-existing-branch'

"git worktree add" learned to check out an existing branch.

* tg/worktree-add-existing-branch:
  worktree: teach "add" to check out existing branches
  worktree: factor out dwim_branch function
  worktree: improve message when creating a new worktree
  worktree: remove extra members from struct add_opts

Documentation/git-worktree.txt

@@ -61,8 +61,13 @@ $ git worktree add --track -b <branch> <path> <remote>/<branch>
 ------------
 +
 If `<commit-ish>` is omitted and neither `-b` nor `-B` nor `--detach` used,
-then, as a convenience, a new branch based at HEAD is created automatically,
-as if `-b $(basename <path>)` was specified.
+then, as a convenience, the new worktree is associated with a branch
+(call it `<branch>`) named after `$(basename <path>)`.  If `<branch>`
+doesn't exist, a new branch based on HEAD is automatically created as
+if `-b <branch>` was given.  If `<branch>` does exist, it will be
+checked out in the new worktree, if it's not checked out anywhere
+else, otherwise the command will refuse to create the worktree (unless
+`--force` is used).
 
 list::
 

builtin/worktree.c

@@ -29,8 +29,6 @@ struct add_opts {
 	int detach;
 	int checkout;
 	int keep_locked;
-	const char *new_branch;
-	int force_new_branch;
 };
 
 static int show_only;
@@ -298,8 +296,6 @@ static int add_worktree(const char *path, const char *refname,
 	strbuf_addf(&sb, "%s/commondir", sb_repo.buf);
 	write_file(sb.buf, "../..");
 
-	fprintf_ln(stderr, _("Preparing %s (identifier %s)"), path, name);
-
 	argv_array_pushf(&child_env, "%s=%s", GIT_DIR_ENVIRONMENT, sb_git.buf);
 	argv_array_pushf(&child_env, "%s=%s", GIT_WORK_TREE_ENVIRONMENT, path);
 	cp.git_cmd = 1;
@@ -366,18 +362,75 @@ done:
 	return ret;
 }
 
+static void print_preparing_worktree_line(int detach,
+					  const char *branch,
+					  const char *new_branch,
+					  int force_new_branch)
+{
+	if (force_new_branch) {
+		struct commit *commit = lookup_commit_reference_by_name(new_branch);
+		if (!commit)
+			printf_ln(_("Preparing worktree (new branch '%s')"), new_branch);
+		else
+			printf_ln(_("Preparing worktree (resetting branch '%s'; was at %s)"),
+				  new_branch,
+				  find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV));
+	} else if (new_branch) {
+		printf_ln(_("Preparing worktree (new branch '%s')"), new_branch);
+	} else {
+		struct strbuf s = STRBUF_INIT;
+		if (!detach && !strbuf_check_branch_ref(&s, branch) &&
+		    ref_exists(s.buf))
+			printf_ln(_("Preparing worktree (checking out '%s')"),
+				  branch);
+		else {
+			struct commit *commit = lookup_commit_reference_by_name(branch);
+			if (!commit)
+				die(_("invalid reference: %s"), branch);
+			printf_ln(_("Preparing worktree (detached HEAD %s)"),
+				  find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV));
+		}
+		strbuf_release(&s);
+	}
+}
+
+static const char *dwim_branch(const char *path, const char **new_branch)
+{
+	int n;
+	const char *s = worktree_basename(path, &n);
+	const char *branchname = xstrndup(s, n);
+	struct strbuf ref = STRBUF_INIT;
+
+	UNLEAK(branchname);
+	if (!strbuf_check_branch_ref(&ref, branchname) &&
+	    ref_exists(ref.buf)) {
+		strbuf_release(&ref);
+		return branchname;
+	}
+
+	*new_branch = branchname;
+	if (guess_remote) {
+		struct object_id oid;
+		const char *remote =
+			unique_tracking_name(*new_branch, &oid);
+		return remote;
+	}
+	return NULL;
+}
+
 static int add(int ac, const char **av, const char *prefix)
 {
 	struct add_opts opts;
 	const char *new_branch_force = NULL;
 	char *path;
 	const char *branch;
+	const char *new_branch = NULL;
 	const char *opt_track = NULL;
 	struct option options[] = {
 		OPT__FORCE(&opts.force,
 			   N_("checkout <branch> even if already checked out in other worktree"),
 			   PARSE_OPT_NOCOMPLETE),
-		OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
+		OPT_STRING('b', NULL, &new_branch, N_("branch"),
 			   N_("create a new branch")),
 		OPT_STRING('B', NULL, &new_branch_force, N_("branch"),
 			   N_("create or reset a branch")),
@@ -395,7 +448,7 @@ static int add(int ac, const char **av, const char *prefix)
 	memset(&opts, 0, sizeof(opts));
 	opts.checkout = 1;
 	ac = parse_options(ac, av, prefix, options, worktree_usage, 0);
-	if (!!opts.detach + !!opts.new_branch + !!new_branch_force > 1)
+	if (!!opts.detach + !!new_branch + !!new_branch_force > 1)
 		die(_("-b, -B, and --detach are mutually exclusive"));
 	if (ac < 1 || ac > 2)
 		usage_with_options(worktree_usage, options);
@@ -406,33 +459,25 @@ static int add(int ac, const char **av, const char *prefix)
 	if (!strcmp(branch, "-"))
 		branch = "@{-1}";
 
-	opts.force_new_branch = !!new_branch_force;
-	if (opts.force_new_branch) {
+	if (new_branch_force) {
 		struct strbuf symref = STRBUF_INIT;
 
-		opts.new_branch = new_branch_force;
+		new_branch = new_branch_force;
 
 		if (!opts.force &&
-		    !strbuf_check_branch_ref(&symref, opts.new_branch) &&
+		    !strbuf_check_branch_ref(&symref, new_branch) &&
 		    ref_exists(symref.buf))
 			die_if_checked_out(symref.buf, 0);
 		strbuf_release(&symref);
 	}
 
-	if (ac < 2 && !opts.new_branch && !opts.detach) {
-		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 && !new_branch && !opts.detach) {
+		const char *s = dwim_branch(path, &new_branch);
+		if (s)
+			branch = s;
 	}
 
-	if (ac == 2 && !opts.new_branch && !opts.detach) {
+	if (ac == 2 && !new_branch && !opts.detach) {
 		struct object_id oid;
 		struct commit *commit;
 		const char *remote;
@@ -441,25 +486,27 @@ static int add(int ac, const char **av, const char *prefix)
 		if (!commit) {
 			remote = unique_tracking_name(branch, &oid);
 			if (remote) {
-				opts.new_branch = branch;
+				new_branch = branch;
 				branch = remote;
 			}
 		}
 	}
 
-	if (opts.new_branch) {
+	print_preparing_worktree_line(opts.detach, branch, new_branch, !!new_branch_force);
+
+	if (new_branch) {
 		struct child_process cp = CHILD_PROCESS_INIT;
 		cp.git_cmd = 1;
 		argv_array_push(&cp.args, "branch");
-		if (opts.force_new_branch)
+		if (new_branch_force)
 			argv_array_push(&cp.args, "--force");
-		argv_array_push(&cp.args, opts.new_branch);
+		argv_array_push(&cp.args, new_branch);
 		argv_array_push(&cp.args, branch);
 		if (opt_track)
 			argv_array_push(&cp.args, opt_track);
 		if (run_command(&cp))
 			return -1;
-		branch = opts.new_branch;
+		branch = new_branch;
 	} else if (opt_track) {
 		die(_("--[no-]track can only be used if a new branch is created"));
 	}

t/t2025-worktree-add.sh

@@ -198,13 +198,25 @@ test_expect_success '"add" with <branch> omitted' '
 	test_cmp_rev HEAD bat
 '
 
-test_expect_success '"add" auto-vivify does not clobber existing branch' '
-	test_commit c1 &&
-	test_commit c2 &&
-	git branch precious HEAD~1 &&
-	test_must_fail git worktree add precious &&
-	test_cmp_rev HEAD~1 precious &&
-	test_path_is_missing precious
+test_expect_success '"add" checks out existing branch of dwimd name' '
+	git branch dwim HEAD~1 &&
+	git worktree add dwim &&
+	test_cmp_rev HEAD~1 dwim &&
+	(
+		cd dwim &&
+		test_cmp_rev HEAD dwim
+	)
+'
+
+test_expect_success '"add <path>" dwim fails with checked out branch' '
+	git checkout -b test-branch &&
+	test_must_fail git worktree add test-branch &&
+	test_path_is_missing test-branch
+'
+
+test_expect_success '"add --force" with existing dwimd name doesnt die' '
+	git checkout test-branch &&
+	git worktree add --force test-branch
 '
 
 test_expect_success '"add" no auto-vivify with --detach and <branch> omitted' '