Warn about missing backslashes during load

* src/lread.c (load_warn_unescaped_character_literals, Fload, read1)
(syms_of_lread): Warn if unescaped character literals are
found (Bug#20152).
* lisp/emacs-lisp/bytecomp.el (byte-compile-from-buffer): Check for
unescaped character literals during byte compilation.
* test/src/lread-tests.el (lread-tests--unescaped-char-literals): New
unit test.
(lread-tests--with-temp-file, lread-tests--last-message): Helper
functions for unit test.
* test/lisp/emacs-lisp/bytecomp-tests.el
(bytecomp-tests--unescaped-char-literals): New unit test.
* test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp-tests--with-temp-file):
Helper macro for unit test.

4 files changed, 96 insertions, 0 deletions

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 15dc24060aa..25102548a9d 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -2027,12 +2027,19 @@ With argument ARG, insert value in current buffer after the form."
           (setq byte-compile-read-position (point)
                 byte-compile-last-position byte-compile-read-position)
           (let* ((old-style-backquotes nil)
+                 (lread--unescaped-character-literals nil)
                  (form (read inbuffer)))
             ;; Warn about the use of old-style backquotes.
             (when 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."))
+            (when lread--unescaped-character-literals
+              (byte-compile-warn
+               "unescaped character literals %s detected!"
+               (mapconcat #'string
+                          (sort lread--unescaped-character-literals #'<)
+                          ", ")))
             (byte-compile-toplevel-file-form form)))
         ;; Compile pending forms at end of file.
         (byte-compile-flush-pending)
diff --git a/src/lread.c b/src/lread.c
index 3b2e123dd39..6467043b1da 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -955,6 +955,21 @@ load_warn_old_style_backquotes (Lisp_Object file)
     }
 }
 
+static void
+load_warn_unescaped_character_literals (Lisp_Object file)
+{
+  if (NILP (Vlread_unescaped_character_literals)) return;
+  CHECK_CONS (Vlread_unescaped_character_literals);
+  AUTO_STRING (format,
+               "Loading `%s': unescaped character literals %s detected!");
+  AUTO_STRING (separator, ", ");
+  CALLN (Fmessage,
+         format, file,
+         Fmapconcat (Qstring,
+                     Fsort (Vlread_unescaped_character_literals, Qlss),
+                     separator));
+}
+
 DEFUN ("get-load-suffixes", Fget_load_suffixes, Sget_load_suffixes, 0, 0, 0,
        doc: /* Return the suffixes that `load' should try if a suffix is \
 required.
@@ -1202,6 +1217,11 @@ Return t if the file exists and loads successfully.  */)
   specbind (Qold_style_backquotes, Qnil);
   record_unwind_protect (load_warn_old_style_backquotes, file);
 
+  /* Check for the presence of unescaped character literals and warn
+     about them. */
+  specbind (Qlread_unescaped_character_literals, Qnil);
+  record_unwind_protect (load_warn_unescaped_character_literals, file);
+
   int is_elc;
   if ((is_elc = suffix_p (found, ".elc")) != 0
       /* version = 1 means the file is empty, in which case we can
@@ -3092,6 +3112,16 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
         if (c == ' ' || c == '\t')
           return make_number (c);
 
+        if (c == '(' || c == ')' || c == '[' || c == ']'
+            || c == '"' || c == ';')
+          {
+            CHECK_LIST (Vlread_unescaped_character_literals);
+            Lisp_Object char_obj = make_natnum (c);
+            if (NILP (Fmemq (char_obj, Vlread_unescaped_character_literals)))
+              Vlread_unescaped_character_literals =
+                Fcons (char_obj, Vlread_unescaped_character_literals);
+          }
+
         if (c == '\\')
           c = read_escape (readcharfun, 0);
         modifiers = c & CHAR_MODIFIER_MASK;
@@ -4815,6 +4845,16 @@ variables, this must be set in the first line of a file.  */);
   Vold_style_backquotes = Qnil;
   DEFSYM (Qold_style_backquotes, "old-style-backquotes");
 
+  DEFVAR_LISP ("lread--unescaped-character-literals",
+               Vlread_unescaped_character_literals,
+               doc: /* List of deprecated unescaped character literals encountered by `read'.
+For internal use only.  */);
+  Vlread_unescaped_character_literals = Qnil;
+  DEFSYM (Qlread_unescaped_character_literals,
+          "lread--unescaped-character-literals");
+
+  DEFSYM (Qlss, "<");
+
   DEFVAR_BOOL ("load-prefer-newer", load_prefer_newer,
                doc: /* Non-nil means `load' prefers the newest version of a file.
 This applies when a filename suffix is not explicitly specified and
diff --git a/test/lisp/emacs-lisp/bytecomp-tests.el b/test/lisp/emacs-lisp/bytecomp-tests.el
index e8feec31d26..3624904753c 100644
--- a/test/lisp/emacs-lisp/bytecomp-tests.el
+++ b/test/lisp/emacs-lisp/bytecomp-tests.el
@@ -506,6 +506,29 @@ bytecompiled code, and their results compared.")
   (dolist (pat bytecomp-lexbind-tests)
     (should (bytecomp-lexbind-check-1 pat))))
 
+(defmacro bytecomp-tests--with-temp-file (file-name-var &rest body)
+  (declare (indent 1))
+  (cl-check-type file-name-var symbol)
+  `(let ((,file-name-var (make-temp-file "emacs")))
+     (unwind-protect
+         (progn ,@body)
+       (delete-file ,file-name-var))))
+
+(ert-deftest bytecomp-tests--unescaped-char-literals ()
+  "Check that byte compiling warns about unescaped character
+literals (Bug#20852)."
+  (should (boundp 'lread--unescaped-character-literals))
+  (bytecomp-tests--with-temp-file source
+    (write-region "(list ?) ?( ?; ?\" ?[ ?])" 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 (concat "unescaped character literals "
+                                     "\", (, ), ;, [, ] detected!"))))))))
+
 ;; Local Variables:
 ;; no-byte-compile: t
 ;; End:
diff --git a/test/src/lread-tests.el b/test/src/lread-tests.el
index 27f967f045b..84342348d45 100644
--- a/test/src/lread-tests.el
+++ b/test/src/lread-tests.el
@@ -116,4 +116,30 @@
   (should (equal '(#s(foo) #s(foo))
                  (read "(#1=#s(foo) #1#)"))))
 
+(defmacro lread-tests--with-temp-file (file-name-var &rest body)
+  (declare (indent 1))
+  (cl-check-type file-name-var symbol)
+  `(let ((,file-name-var (make-temp-file "emacs")))
+     (unwind-protect
+         (progn ,@body)
+       (delete-file ,file-name-var))))
+
+(defun lread-tests--last-message ()
+  (with-current-buffer "*Messages*"
+    (save-excursion
+      (goto-char (point-max))
+      (skip-chars-backward "\n")
+      (buffer-substring (line-beginning-position) (point)))))
+
+(ert-deftest lread-tests--unescaped-char-literals ()
+  "Check that loading warns about unescaped character
+literals (Bug#20852)."
+  (lread-tests--with-temp-file file-name
+    (write-region "?) ?( ?; ?\" ?[ ?]" 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)
+                           "unescaped character literals "
+                           "\", (, ), ;, [, ] detected!")))))
+
 ;;; lread-tests.el ends here