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.

1 files changed, 40 insertions, 0 deletions

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