master 2e81e57: * src/lread.c: Remove old-style backquotes support

[Stefan Monnier]

branch: master
commit 2e81e5733db3b8b88a246d08671b828654cd6950
Author: Stefan Monnier <address@hidden>
Commit: Stefan Monnier <address@hidden>

    * src/lread.c: Remove old-style backquotes support
    
    (new_backquote_flag): Delete variable.
    (load_error_old_style_backquotes): Delete function.
    (force_new_style_backquotes): Delete variable.
    (read_internal_start): Don't obey it any more.
---
 etc/NEWS    |   2 ++
 src/lread.c | 102 ++++++++----------------------------------------------------
 2 files changed, 15 insertions(+), 89 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 82de05e..8737bb7 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -173,6 +173,8 @@ by mistake and were not useful to Lisp code.
 
 * Lisp Changes in Emacs 28.1
 
+** Remove final remaining traces of old-style backquotes
+
 ** The module header 'emacs-module.h' now contains type aliases
 'emacs_function' and 'emacs_finalizer' for module functions and
 finalizers, respectively.
diff --git a/src/lread.c b/src/lread.c
index 69dd739..c124d5a 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -152,12 +152,6 @@ static ptrdiff_t prev_saved_doc_string_length;
 /* This is the file position that string came from.  */
 static file_offset prev_saved_doc_string_position;
 
-/* True means inside a new-style backquote with no surrounding
-   parentheses.  Fread initializes this to the value of
-   `force_new_style_backquotes', so we need not specbind it or worry
-   about what happens to it when there is an error.  */
-static bool new_backquote_flag;
-
 /* A list of file names for files being loaded in Fload.  Used to
    check for recursive loads.  */
 
@@ -1035,18 +1029,6 @@ load_error_handler (Lisp_Object data)
   return Qnil;
 }
 
-static AVOID
-load_error_old_style_backquotes (void)
-{
-  if (NILP (Vload_file_name))
-    xsignal1 (Qerror, build_string ("Old-style backquotes detected!"));
-  else
-    {
-      AUTO_STRING (format, "Loading `%s': old-style backquotes detected!");
-      xsignal1 (Qerror, CALLN (Fformat_message, format, Vload_file_name));
-    }
-}
-
 static void
 load_warn_unescaped_character_literals (Lisp_Object file)
 {
@@ -2283,7 +2265,6 @@ read_internal_start (Lisp_Object stream, Lisp_Object 
start, Lisp_Object end)
   Lisp_Object retval;
 
   readchar_count = 0;
-  new_backquote_flag = force_new_style_backquotes;
   /* We can get called from readevalloop which may have set these
      already.  */
   if (! HASH_TABLE_P (read_objects_map)
@@ -3271,70 +3252,24 @@ read1 (Lisp_Object readcharfun, int *pch, bool 
first_in_list)
       return list2 (Qquote, read0 (readcharfun));
 
     case '`':
-      {
-       int next_char = READCHAR;
-       UNREAD (next_char);
-       /* Transition from old-style to new-style:
-          If we see "(`" it used to mean old-style, which usually works
-          fine because ` should almost never appear in such a position
-          for new-style.  But occasionally we need "(`" to mean new
-          style, so we try to distinguish the two by the fact that we
-          can either write "( `foo" or "(` foo", where the first
-          intends to use new-style whereas the second intends to use
-          old-style.  For Emacs-25, we should completely remove this
-          first_in_list exception (old-style can still be obtained via
-          "(\`" anyway).  */
-       if (!new_backquote_flag && first_in_list && next_char == ' ')
-         load_error_old_style_backquotes ();
-       else
-         {
-           Lisp_Object value;
-           bool saved_new_backquote_flag = new_backquote_flag;
-
-           new_backquote_flag = 1;
-           value = read0 (readcharfun);
-           new_backquote_flag = saved_new_backquote_flag;
+      return list2 (Qbackquote, read0 (readcharfun));
 
-           return list2 (Qbackquote, value);
-         }
-      }
     case ',':
       {
-       int next_char = READCHAR;
-       UNREAD (next_char);
-       /* Transition from old-style to new-style:
-           It used to be impossible to have a new-style , other than within
-          a new-style `.  This is sufficient when ` and , are used in the
-          normal way, but ` and , can also appear in args to macros that
-          will not interpret them in the usual way, in which case , may be
-          used without any ` anywhere near.
-          So we now use the same heuristic as for backquote: old-style
-          unquotes are only recognized when first on a list, and when
-          followed by a space.
-          Because it's more difficult to peek 2 chars ahead, a new-style
-          ,@ can still not be used outside of a `, unless it's in the middle
-          of a list.  */
-       if (new_backquote_flag
-           || !first_in_list
-           || (next_char != ' ' && next_char != '@'))
-         {
-           Lisp_Object comma_type = Qnil;
-           Lisp_Object value;
-           int ch = READCHAR;
-
-           if (ch == '@')
-             comma_type = Qcomma_at;
-           else
-             {
-               if (ch >= 0) UNREAD (ch);
-               comma_type = Qcomma;
-             }
+       Lisp_Object comma_type = Qnil;
+       Lisp_Object value;
+       int ch = READCHAR;
 
-           value = read0 (readcharfun);
-           return list2 (comma_type, value);
-         }
+       if (ch == '@')
+         comma_type = Qcomma_at;
        else
-         load_error_old_style_backquotes ();
+         {
+           if (ch >= 0) UNREAD (ch);
+           comma_type = Qcomma;
+         }
+
+       value = read0 (readcharfun);
+       return list2 (comma_type, value);
       }
     case '?':
       {
@@ -5065,17 +5000,6 @@ Note that if you customize this, obviously it will not 
affect files
 that are loaded before your customizations are read!  */);
   load_prefer_newer = 0;
 
-  DEFVAR_BOOL ("force-new-style-backquotes", force_new_style_backquotes,
-               doc: /* Non-nil means to always use the current syntax for 
backquotes.
-If nil, `load' and `read' raise errors when encountering some
-old-style variants of backquote and comma.  If non-nil, these
-constructs are always interpreted as described in the Info node
-`(elisp)Backquote', even if that interpretation is incompatible with
-previous versions of Emacs.  Setting this variable to non-nil makes
-Emacs compatible with the behavior planned for Emacs 28.  In Emacs 28,
-this variable will become obsolete.  */);
-  force_new_style_backquotes = false;
-
   /* Vsource_directory was initialized in init_lread.  */
 
   DEFSYM (Qcurrent_load_list, "current-load-list");