Merge branch 'cb/checkout-same-branch-twice' into seen

"git checkout -B $branch" failed to protect against checking out
a branch that is checked out elsewhere, unlike "git branch -f" did.

* cb/checkout-same-branch-twice:
  checkout/switch: disallow checking out same branch in multiple worktrees

Author: gitster

builtin/checkout.c

@@ -1476,7 +1476,8 @@ static void die_if_some_operation_in_progress(void)
 }
 
 static int checkout_branch(struct checkout_opts *opts,
-			   struct branch_info *new_branch_info)
+			   struct branch_info *new_branch_info,
+			   char *check_branch_path)
 {
 	if (opts->pathspec.nr)
 		die(_("paths cannot be used with switching branches"));
@@ -1535,13 +1536,13 @@ static int checkout_branch(struct checkout_opts *opts,
 	if (!opts->can_switch_when_in_progress)
 		die_if_some_operation_in_progress();
 
-	if (new_branch_info->path && !opts->force_detach && !opts->new_branch &&
-	    !opts->ignore_other_worktrees) {
+	if (!opts->ignore_other_worktrees && !opts->force_detach &&
+	    check_branch_path && ref_exists(check_branch_path)) {
 		int flag;
 		char *head_ref = resolve_refdup("HEAD", 0, NULL, &flag);
-		if (head_ref &&
-		    (!(flag & REF_ISSYMREF) || strcmp(head_ref, new_branch_info->path)))
-			die_if_checked_out(new_branch_info->path, 1);
+		if (opts->new_branch_force || (head_ref &&
+		    (!(flag & REF_ISSYMREF) || strcmp(head_ref, check_branch_path))))
+			die_if_checked_out(check_branch_path, 1);
 		free(head_ref);
 	}
 
@@ -1629,7 +1630,9 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 			 const char * const usagestr[],
 			 struct branch_info *new_branch_info)
 {
+	int ret;
 	int parseopt_flags = 0;
+	char *check_branch_path = NULL;
 
 	opts->overwrite_ignore = 1;
 	opts->prefix = prefix;
@@ -1719,6 +1722,13 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 		opts->new_branch = argv0 + 1;
 	}
 
+	if (opts->new_branch && !opts->ignore_other_worktrees) {
+		struct strbuf buf = STRBUF_INIT;
+
+		strbuf_branchname(&buf, opts->new_branch, INTERPRET_BRANCH_LOCAL);
+		strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
+		check_branch_path = strbuf_detach(&buf, NULL);
+	}
 	/*
 	 * Extract branch name from command line arguments, so
 	 * all that is left is pathspecs.
@@ -1743,6 +1753,9 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 					     new_branch_info, opts, &rev);
 		argv += n;
 		argc -= n;
+
+		if (!opts->ignore_other_worktrees && !check_branch_path && new_branch_info->path)
+			check_branch_path = xstrdup(new_branch_info->path);
 	} else if (!opts->accept_ref && opts->from_treeish) {
 		struct object_id rev;
 
@@ -1819,9 +1832,12 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 	}
 
 	if (opts->patch_mode || opts->pathspec.nr)
-		return checkout_paths(opts, new_branch_info);
+		ret = checkout_paths(opts, new_branch_info);
 	else
-		return checkout_branch(opts, new_branch_info);
+		ret = checkout_branch(opts, new_branch_info, check_branch_path);
+
+	free(check_branch_path);
+	return ret;
 }
 
 int cmd_checkout(int argc, const char **argv, const char *prefix)

t/t2400-worktree-add.sh

@@ -118,32 +118,52 @@ test_expect_success '"add" worktree creating new branch' '
 	)
 '
 
-test_expect_success 'die the same branch is already checked out' '
+test_expect_success 'die if the same branch is already checked out' '
 	(
 		cd here &&
-		test_must_fail git checkout newmain
+		test_must_fail git checkout newmain &&
+		test_must_fail git checkout -B newmain &&
+		test_must_fail git switch newmain &&
+		test_must_fail git switch -C newmain
 	)
 '
 
-test_expect_success SYMLINKS 'die the same branch is already checked out (symlink)' '
+test_expect_success SYMLINKS 'die if the same branch is already checked out (symlink)' '
 	head=$(git -C there rev-parse --git-path HEAD) &&
 	ref=$(git -C there symbolic-ref HEAD) &&
 	rm "$head" &&
 	ln -s "$ref" "$head" &&
 	test_must_fail git -C here checkout newmain
 '
 
-test_expect_success 'not die the same branch is already checked out' '
+test_expect_success 'allow creating multiple worktrees for same branch with force' '
+	git worktree add --force anothernewmain newmain
+'
+
+test_expect_success 'allow checkout/reset from the conflicted branch' '
 	(
 		cd here &&
-		git worktree add --force anothernewmain newmain
+		git checkout -b conflictedmain newmain &&
+		git checkout -B conflictedmain newmain &&
+		git switch -C conflictedmain newmain
+	)
+'
+
+test_expect_success 'and not die on re-checking out current branch even if conflicted' '
+	(
+		cd there &&
+		git checkout newmain &&
+		git switch newmain
 	)
 '
 
-test_expect_success 'not die on re-checking out current branch' '
+test_expect_failure 'unless using force without --ignore-other-worktrees' '
 	(
 		cd there &&
-		git checkout newmain
+		test_must_fail git checkout -B newmain &&
+		test_must_fail git switch -C newmain &&
+		git checkout --ignore-other-worktrees -B newmain &&
+		git switch --ignore-other-worktrees -C newmain
 	)
 '