Remove support for destructive splicing in elisp

* src/lread.c (read1): Don't handle destructive splicing in
backquote expressions (e.g. ",.<identifier>").  (Bug#19790)
(syms_of_lread): Remove Qcomma_dot.
* src/print.c (print_object): Don't check for Qcomma_dot.
* test/src/eval-tests.el
(eval-tests-19790-backquote-comma-dot-substitution): New test.
* etc/NEWS: Announce it.

2 files changed, 1 insertions, 5 deletions

diff --git a/src/lread.c b/src/lread.c
index 151731a81d9..5000b38a015 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -3310,8 +3310,6 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
 
             if (ch == '@')
               comma_type = Qcomma_at;
-            else if (ch == '.')
-              comma_type = Qcomma_dot;
             else
               {
                 if (ch >= 0) UNREAD (ch);
@@ -5080,7 +5078,6 @@ this variable will become obsolete.  */);
   DEFSYM (Qbackquote, "`");
   DEFSYM (Qcomma, ",");
   DEFSYM (Qcomma_at, ",@");
-  DEFSYM (Qcomma_dot, ",.");
 
   DEFSYM (Qinhibit_file_name_operation, "inhibit-file-name-operation");
   DEFSYM (Qascii_character, "ascii-character");
diff --git a/src/print.c b/src/print.c
index 7e5aed82877..77ddd93efba 100644
--- a/src/print.c
+++ b/src/print.c
@@ -2076,8 +2076,7 @@ print_object (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag)
       else if (print_quoted && CONSP (XCDR (obj)) && NILP (XCDR (XCDR (obj)))
                && new_backquote_output
                && (EQ (XCAR (obj), Qcomma)
-                   || EQ (XCAR (obj), Qcomma_at)
-                   || EQ (XCAR (obj), Qcomma_dot)))
+                   || EQ (XCAR (obj), Qcomma_at)))
         {
           print_object (XCAR (obj), printcharfun, false);
           new_backquote_output--;