Fix misc problems with thumbnails on MS-Windows

* lisp/image/image-dired-external.el (image-dired-pngcrush-thumb):
Fix deletion of intermediate file.
(image-dired-cmd-pngcrush-options)
(image-dired-cmd-create-standard-thumbnail-options): Use %u for
file:// URI.
(image-dired--file-URI): New function.
(image-dired-create-thumb-1, image-dired-create-thumb-2)
(image-dired-set-exif-data): Use it to generate correct URI on
MS-Windows.

* src/w32image.c (Fw32image_create_thumbnail): Copy the file names
before mirroring their slashes.

lisp/image/image-dired-external.el

@@ -103,21 +103,24 @@ It optimizes the compression of PNG images.  It also adds PNG textual chunks
 with the information required by the Thumbnail Managing Standard."
   :type '(choice (const :tag "Not Set" nil) file))
 
+;; Note: the "-text" arguments below are according to specification in
+;; https://specifications.freedesktop.org/thumbnail-spec/thumbnail-spec-latest.html#CREATION
 (defcustom image-dired-cmd-pngcrush-options
   `("-q"
-    "-text" "b" "Description" "Thumbnail of file://%f"
-    "-text" "b" "Software" ,(emacs-version)
+    "-text" "b" "Description" "Thumbnail of file://%u"
+    "-text" "b" "Software" ,(string-replace "\n" " " (emacs-version))
     ;; "-text b \"Thumb::Image::Height\" \"%oh\" "
     ;; "-text b \"Thumb::Image::Mimetype\" \"%mime\" "
     ;; "-text b \"Thumb::Image::Width\" \"%ow\" "
     "-text" "b" "Thumb::MTime" "%m"
     ;; "-text b \"Thumb::Size\" \"%b\" "
-    "-text" "b" "Thumb::URI" "file://%f"
+    "-text" "b" "Thumb::URI" "file://%u"
     "%q" "%t")
   "Arguments for `image-dired-cmd-pngcrush-program'.
 The value can use the same %-format specifiers as in
-`image-dired-cmd-create-thumbnail-options', with \"%q\" for a
-temporary file name (typically generated by pnqnq)."
+`image-dired-cmd-create-thumbnail-options', with \"%q\" standing for a
+temporary file name (typically generated by pnqnq),
+and \"%u\" standing for a file URI corresponding to file in \"%f\"."
   :version "26.1"
   :type '(repeat (string :tag "Argument")))
 
@@ -134,20 +137,22 @@ The value can use the same %-format specifiers as in
   :type '(repeat (string :tag "Argument"))
   :link '(url-link "man:optipng(1)"))
 
+;; Note: the "-set" arguments below are according to specification in
+;; https://specifications.freedesktop.org/thumbnail-spec/thumbnail-spec-latest.html#CREATION
 (defcustom image-dired-cmd-create-standard-thumbnail-options
   (let ((opts (list
                "-size" "%wx%h" "%f[0]"
                "-set" "Thumb::MTime" "%m"
-               "-set" "Thumb::URI" "file://%f"
-               "-set" "Description" "Thumbnail of file://%f"
-               "-set" "Software" (emacs-version)
+               "-set" "Thumb::URI" "file://%u"
+               "-set" "Description" "Thumbnail of file://%u"
+               "-set" "Software" (string-replace "\n" " " (emacs-version))
                "-thumbnail" "%wx%h>" "png:%t")))
     (if (executable-find "gm") (cons "convert" opts) opts))
   "Options for creating thumbnails according to the Thumbnail Managing Standard.
 Used with `image-dired-cmd-create-thumbnail-program', if that is available.
 The value can use the same %-format specifiers as in
 `image-dired-cmd-create-thumbnail-options', with \"%m\" for file
-modification time.
+modification time and \"%u\" for the URI of the file in \"%f\".
 On MS-Windows, if the `convert' command is not available, and
 `w32image-create-thumbnail' is used instead, the textual chunks
 specified by the \"-set\" options will not be injected, and instead
@@ -196,6 +201,12 @@ and %v which is replaced by the tag value."
 
 ;;; Util functions
 
+(defun image-dired--file-URI (file)
+  ;; https://en.wikipedia.org/wiki/File_URI_scheme
+  (if (memq system-type '(windows-nt ms-dos))
+      (concat "/" file)
+    file))
+
 (defun image-dired--probe-thumbnail-cmd (cmd)
   "Check whether CMD is usable for thumbnail creation."
   (cond
@@ -327,11 +338,11 @@ on MS-Windows cannot have too many concurrent sub-processes.")
                       (message "command %S %s" (process-command process)
                                (string-replace "\n" "" status))
                     (message "command %S failed with status %s"
-                             process status))
+                             process status)))
                 (when (or (not (processp process))
                           (memq (process-status process) '(exit signal)))
                   (let ((temp (cdr (assq ?q spec))))
-                    (delete-file temp))))))
+                    (delete-file temp)))))
          (proc
           (if (eq system-type 'windows-nt)
               ;; See above for the reasons we don't use 'start-process'
@@ -385,6 +396,7 @@ on MS-Windows cannot have too many concurrent sub-processes.")
          (spec `((?s . ,size) (?w . ,size) (?h . ,size)
                  (?m . ,modif-time)
                  (?f . ,original-file)
+                 (?u . ,(image-dired--file-URI original-file))
                  (?q . ,thumbnail-nq8-file)
                  (?t . ,thumbnail-file)))
          (thumbnail-dir (file-name-directory thumbnail-file))
@@ -471,6 +483,7 @@ file is created by Emacs itself."
                (spec `((?s . ,size) (?w . ,size) (?h . ,size)
                        (?m . ,modif-time)
                        (?f . ,original-file)
+                       (?u . ,(image-dired--file-URI original-file))
                        (?q . ,thumbnail-nq8-file)
                        (?t . ,thumbnail-file))))
           (cond
@@ -611,6 +624,7 @@ default value at the prompt."
   (let ((spec
          (list
           (cons ?f (expand-file-name file))
+          (cons ?u (image-dired--file-URI (expand-file-name file)))
           (cons ?t tag-name)
           (cons ?v tag-value))))
     (apply #'call-process image-dired-cmd-write-exif-data-program nil nil nil