Improve project support for quoted directory names (Bug#47799)

* lisp/progmodes/project.el (project--files-in-directory): Unquote
directory name before passing it to 'find'.
(project--remote-file-names): Requote local filenames if the original
directory is quoted.
* test/lisp/progmodes/project-tests.el (project/quoted-directory): New
unit test.

lisp/progmodes/project.el

@@ -300,7 +300,8 @@ to find the list of ignores for each directory."
          (command (format "%s %s %s -type f %s -print0"
                           find-program
                           ;; In case DIR is a symlink.
-                          (file-name-as-directory localdir)
+                          (file-name-unquote
+                           (file-name-as-directory localdir))
                           (xref--find-ignores-arguments ignores localdir)
                           (if files
                               (concat (shell-quote-argument "(")
@@ -317,10 +318,13 @@ to find the list of ignores for each directory."
            #'string<))))
 
 (defun project--remote-file-names (local-files)
-  "Return LOCAL-FILES as if they were on the system of `default-directory'."
+  "Return LOCAL-FILES as if they were on the system of `default-directory'.
+Also quote LOCAL-FILES if `default-directory' is quoted."
   (let ((remote-id (file-remote-p default-directory)))
     (if (not remote-id)
-        local-files
+        (if (file-name-quoted-p default-directory)
+            (mapcar #'file-name-quote local-files)
+          local-files)
       (mapcar (lambda (file)
                 (concat remote-id file))
               local-files))))

test/lisp/progmodes/project-tests.el

@@ -0,0 +1,44 @@
+;;; project-tests.el --- tests for project.el -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2021  Free Software Foundation, Inc.
+
+;; Keywords:
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Unit tests for progmodes/project.el.
+
+;;; Code:
+
+(require 'project)
+
+(require 'ert)
+
+(ert-deftest project/quoted-directory ()
+  "Check that `project-files' deals with quoted directory
+names (Bug#47799)."
+  (let ((directory (make-temp-file "project-tests-" :directory)))
+    (unwind-protect
+        (let ((project (cons 'transient (file-name-quote directory)))
+              (file (expand-file-name "file" directory)))
+          (make-empty-file file)
+          (should (equal (project-files project)
+                         (list (file-name-quote file)))))
+      (delete-directory directory :recursive))))
+
+;;; project-tests.el ends here