Signal error for symbol names with strange quotes (Bug#2967)

* src/lread.c (read1): Signal an error when a symbol starts with a
non-escaped quote-like character.
* test/src/lread-tests.el (lread-tests--funny-quote-symbols): New
test.
* etc/NEWS: Announce change.

3 files changed, 39 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 50945f0cfa3..4324d87991f 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1154,6 +1154,10 @@ instead of its first.
 renamed to 'lread--old-style-backquotes'.  No user code should use
 this variable.
 
+** To avoid confusion caused by "smart quotes", the reader no longer
+accepts Lisp symbols which begin with the following quotation
+characters: ‘’‛“”‟〞＂＇, unless they are escaped with backslash.
+
 +++
 ** Module functions are now implemented slightly differently; in
 particular, the function 'internal--module-call' has been removed.
diff --git a/src/lread.c b/src/lread.c
index 901e40b3489..dbaadce4b40 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -3479,6 +3479,24 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
             if (! NILP (result))
               return unbind_to (count, result);
           }
+        if (!quoted && multibyte)
+          {
+            int ch = STRING_CHAR ((unsigned char *) read_buffer);
+            switch (ch)
+              {
+              case 0x2018: /* LEFT SINGLE QUOTATION MARK */
+              case 0x2019: /* RIGHT SINGLE QUOTATION MARK */
+              case 0x201B: /* SINGLE HIGH-REVERSED-9 QUOTATION MARK */
+              case 0x201C: /* LEFT DOUBLE QUOTATION MARK */
+              case 0x201D: /* RIGHT DOUBLE QUOTATION MARK */
+              case 0x201F: /* DOUBLE HIGH-REVERSED-9 QUOTATION MARK */
+              case 0x301E: /* DOUBLE PRIME QUOTATION MARK */
+              case 0xFF02: /* FULLWIDTH QUOTATION MARK */
+              case 0xFF07: /* FULLWIDTH APOSTROPHE */
+                xsignal2 (Qinvalid_read_syntax, build_string ("strange quote"),
+                          CALLN (Fstring, make_number (ch)));
+              }
+          }
         {
           Lisp_Object result;
           ptrdiff_t nbytes = p - read_buffer;
diff --git a/test/src/lread-tests.el b/test/src/lread-tests.el
index a0a317feeeb..dd5a2003b41 100644
--- a/test/src/lread-tests.el
+++ b/test/src/lread-tests.el
@@ -142,6 +142,23 @@ literals (Bug#20852)."
                            "unescaped character literals "
                            "`?\"', `?(', `?)', `?;', `?[', `?]' detected!")))))
 
+(ert-deftest lread-tests--funny-quote-symbols ()
+  "Check that 'smart quotes' or similar trigger errors in symbol names."
+  (dolist (quote-char
+           '(#x2018 ;; LEFT SINGLE QUOTATION MARK
+             #x2019 ;; RIGHT SINGLE QUOTATION MARK
+             #x201B ;; SINGLE HIGH-REVERSED-9 QUOTATION MARK
+             #x201C ;; LEFT DOUBLE QUOTATION MARK
+             #x201D ;; RIGHT DOUBLE QUOTATION MARK
+             #x201F ;; DOUBLE HIGH-REVERSED-9 QUOTATION MARK
+             #x301E ;; DOUBLE PRIME QUOTATION MARK
+             #xFF02 ;; FULLWIDTH QUOTATION MARK
+             #xFF07 ;; FULLWIDTH APOSTROPHE
+             ))
+    (let ((str (format "%cfoo" quote-char)))
+     (should-error (read str) :type 'invalid-read-syntax)
+     (should (eq (read (concat "\\" str)) (intern str))))))
+
 (ert-deftest lread-test-bug26837 ()
   "Test for http://debbugs.gnu.org/26837 ."
   (let ((load-path (cons