[PATCH] Make `old-style-backquotes' variable internal

[Philipp <phil07c1@gmail.com>]

* src/lread.c (load_warn_old_style_backquotes, Fload, read1)
(syms_of_lread): Rename `old-style-backquotes' to
`lread--old-style-backquotes', and clarify that it's for internal
use only.
* lisp/emacs-lisp/bytecomp.el (byte-compile-from-buffer): Rename
variable.
* test/src/lread-tests.el (lread-tests--old-style-backquotes): Add
unit test.
* emacs-lisp/bytecomp-tests.el
(bytecomp-tests--old-style-backquotes): Add unit test.
---
 lisp/emacs-lisp/bytecomp.el            |  4 ++--
 src/lread.c                            | 17 +++++++++--------
 test/lisp/emacs-lisp/bytecomp-tests.el | 15 +++++++++++++++
 test/src/lread-tests.el                |  9 +++++++++
 4 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 25102548a9..3fd3f5a1b8 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -2026,11 +2026,11 @@ byte-compile-from-buffer
 		 (not (eobp)))
 	  (setq byte-compile-read-position (point)
 		byte-compile-last-position byte-compile-read-position)
-	  (let* ((old-style-backquotes nil)
+	  (let* ((lread--old-style-backquotes nil)
                  (lread--unescaped-character-literals nil)
                  (form (read inbuffer)))
             ;; Warn about the use of old-style backquotes.
-            (when old-style-backquotes
+            (when lread--old-style-backquotes
               (byte-compile-warn "!! The file uses old-style backquotes !!
 This functionality has been obsolete for more than 10 years already
 and will be removed soon.  See (elisp)Backquote in the manual."))
diff --git a/src/lread.c b/src/lread.c
index 6467043b1d..3cf8ef5a4e 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -948,7 +948,7 @@ load_error_handler (Lisp_Object data)
 static void
 load_warn_old_style_backquotes (Lisp_Object file)
 {
-  if (!NILP (Vold_style_backquotes))
+  if (!NILP (Vlread_old_style_backquotes))
     {
       AUTO_STRING (format, "Loading `%s': old-style backquotes detected!");
       CALLN (Fmessage, format, file);
@@ -1214,7 +1214,7 @@ Return t if the file exists and loads successfully.  */)
   version = -1;
 
   /* Check for the presence of old-style quotes and warn about them.  */
-  specbind (Qold_style_backquotes, Qnil);
+  specbind (Qlread_old_style_backquotes, Qnil);
   record_unwind_protect (load_warn_old_style_backquotes, file);
 
   /* Check for the presence of unescaped character literals and warn
@@ -3037,7 +3037,7 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
 	   "(\`" anyway).  */
 	if (!new_backquote_flag && first_in_list && next_char == ' ')
 	  {
-	    Vold_style_backquotes = Qt;
+	    Vlread_old_style_backquotes = Qt;
 	    goto default_label;
 	  }
 	else
@@ -3091,7 +3091,7 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
 	  }
 	else
 	  {
-	    Vold_style_backquotes = Qt;
+	    Vlread_old_style_backquotes = Qt;
 	    goto default_label;
 	  }
       }
@@ -4840,10 +4840,11 @@ variables, this must be set in the first line of a file.  */);
 	       doc: /* List of buffers being read from by calls to `eval-buffer' and `eval-region'.  */);
   Veval_buffer_list = Qnil;
 
-  DEFVAR_LISP ("old-style-backquotes", Vold_style_backquotes,
-	       doc: /* Set to non-nil when `read' encounters an old-style backquote.  */);
-  Vold_style_backquotes = Qnil;
-  DEFSYM (Qold_style_backquotes, "old-style-backquotes");
+  DEFVAR_LISP ("lread--old-style-backquotes", Vlread_old_style_backquotes,
+	       doc: /* Set to non-nil when `read' encounters an old-style backquote.
+For internal use only.  */);
+  Vlread_old_style_backquotes = Qnil;
+  DEFSYM (Qlread_old_style_backquotes, "lread--old-style-backquotes");
 
   DEFVAR_LISP ("lread--unescaped-character-literals",
                Vlread_unescaped_character_literals,
diff --git a/test/lisp/emacs-lisp/bytecomp-tests.el b/test/lisp/emacs-lisp/bytecomp-tests.el
index 3624904753..a83c998a59 100644
--- a/test/lisp/emacs-lisp/bytecomp-tests.el
+++ b/test/lisp/emacs-lisp/bytecomp-tests.el
@@ -529,6 +529,21 @@ bytecomp-tests--with-temp-file
                        (list (concat "unescaped character literals "
                                      "\", (, ), ;, [, ] detected!"))))))))
 
+(ert-deftest bytecomp-tests--old-style-backquotes ()
+  "Check that byte compiling warns about old-style backquotes."
+  (should (boundp 'lread--old-style-backquotes))
+  (bytecomp-tests--with-temp-file source
+    (write-region "(` (a b))" nil source)
+    (bytecomp-tests--with-temp-file destination
+      (let* ((byte-compile-dest-file-function (lambda (_) destination))
+            (byte-compile-error-on-warn t)
+            (byte-compile-debug t)
+            (err (should-error (byte-compile-file source))))
+        (should (equal (cdr err)
+                       (list "!! The file uses old-style backquotes !!
+This functionality has been obsolete for more than 10 years already
+and will be removed soon.  See (elisp)Backquote in the manual.")))))))
+
 ;; Local Variables:
 ;; no-byte-compile: t
 ;; End:
diff --git a/test/src/lread-tests.el b/test/src/lread-tests.el
index 84342348d4..e45d184cad 100644
--- a/test/src/lread-tests.el
+++ b/test/src/lread-tests.el
@@ -142,4 +142,13 @@ lread-tests--last-message
                            "unescaped character literals "
                            "\", (, ), ;, [, ] detected!")))))
 
+(ert-deftest lread-tests--old-style-backquotes ()
+  "Check that loading warns about old-style backquotes."
+  (lread-tests--with-temp-file file-name
+    (write-region "(` (a b))" nil file-name)
+    (should (equal (load file-name nil :nomessage :nosuffix) t))
+    (should (equal (lread-tests--last-message)
+                   (concat (format-message "Loading `%s': " file-name)
+                           "old-style backquotes detected!")))))
+
 ;;; lread-tests.el ends here
-- 
2.12.2