factor the handling of m4 escaping

The conversion from @ to @@ and so forth is coded is too many
different places.  Factor, a bit.

* src/scan-code.l: Instead of duplicating the logic of obstack_escape,
use it.
It sure is less efficient, but the cost is negligible.
This allows to factor rules that are alike.
And to factor some start-condition clauses.
* tests/input.at (Stray $ or @): New.
* NEWS: Document it.

NEWS

@@ -22,6 +22,12 @@ GNU Bison NEWS
 
 *** glr.cc: set_debug_level and debug_level work as expected.
 
+*** Stray @ or $ in actions
+
+  While Bison used to warn about stray $ or @ in action rules, it did not
+  for other actions such as printers, destructors, or initial actions.  It
+  now does.
+
 ** Type names in printers and destructors
 
   For consistency with rule actions, it is now possible to qualify $$ by a

src/scan-code.l

@@ -103,7 +103,10 @@ ref      -?[0-9]+|{id}|"["{id}"]"|"$"
      ';', or a C preprocessor directive, and that whitespaces and
      comments do not affect this flag.  Note that '{' does not need a
      semicolon because of '{}'.  A semicolon may be needed before a
-     cpp directive, but don't bother.  */
+     cpp directive, but don't bother.
+
+     While it is maintained in several start-conditions (factoring
+     opportunities), it is meaningful only for SC_RULE_ACTION. */
   bool need_semicolon = false;
 
   /* Whether in a C preprocessor directive.  Don't use a start condition
@@ -181,6 +184,15 @@ ref      -?[0-9]+|{id}|"["{id}"]"|"$"
     STRING_GROW;
     BEGIN SC_LINE_COMMENT;
   }
+  [$@]  {
+    warn_at (*loc, _("stray '%s'"), yytext);
+    obstack_escape (&obstack_for_string, yytext);
+    need_semicolon = true;
+  }
+  [\[\]]  {
+    obstack_escape (&obstack_for_string, yytext);
+    need_semicolon = true;
+  }
 }
 
 <SC_RULE_ACTION>
@@ -199,24 +211,6 @@ ref      -?[0-9]+|{id}|"["{id}"]"|"$"
       obstack_sgrow (&obstack_for_string, ref_tail_fields);
     need_semicolon = true;
   }
-  "$"  {
-    warn_at (*loc, _("stray '$'"));
-    obstack_sgrow (&obstack_for_string, "$][");
-    need_semicolon = true;
-  }
-  "@"  {
-    warn_at (*loc, _("stray '@'"));
-    obstack_sgrow (&obstack_for_string, "@@");
-    need_semicolon = true;
-  }
-  "["  {
-    obstack_sgrow (&obstack_for_string, "@{");
-    need_semicolon = true;
-  }
-  "]"  {
-    obstack_sgrow (&obstack_for_string, "@}");
-    need_semicolon = true;
-  }
 
   ";"  STRING_GROW;                 need_semicolon = false;
   "{"  STRING_GROW; ++braces_level; need_semicolon = false;
@@ -281,30 +275,18 @@ ref      -?[0-9]+|{id}|"["{id}"]"|"$"
 }
 
 
-  /*-----------------------------------------.
-  | Escape M4 quoting characters in C code.  |
-  `-----------------------------------------*/
-
 <*>
 {
-  \$	obstack_sgrow (&obstack_for_string, "$][");
+  /* Escape M4 quoting characters in C code.  */
-  \@	obstack_sgrow (&obstack_for_string, "@@");
+  [$@\[\]]    obstack_escape (&obstack_for_string, yytext);
-  \[	obstack_sgrow (&obstack_for_string, "@{");
+
-  \]	obstack_sgrow (&obstack_for_string, "@}");
+  /* By default, grow the string obstack with the input.  */
+  .|\n        STRING_GROW;
+
+  /* End of processing. */
+  <<EOF>>     STRING_FINISH; return last_string;
 }
 
-  /*-----------------------------------------------------.
-  | By default, grow the string obstack with the input.  |
-  `-----------------------------------------------------*/
-
-<*>.|\n	STRING_GROW;
-
- /* End of processing. */
-<*><<EOF>>	 {
-                   STRING_FINISH;
-                   return last_string;
-                 }
-
 %%
 
 static inline bool

tests/input.at

@@ -1371,6 +1371,36 @@ m4_popdef([AT_TEST])
 AT_CLEANUP
 
 
+## -------------- ##
+## Stray $ or @.  ##
+## -------------- ##
+
+AT_SETUP([[Stray $ or @]])
+
+AT_DATA_GRAMMAR([[input.y]],
+[[%token TOK
+%destructor     { $%; @%; } <*>;
+%initial-action { $%; @%; };
+%printer        { $%; @%; } <*>;
+%%
+exp: TOK        { $%; @%; };
+]])
+
+AT_BISON_CHECK([[input.y]], 0, [],
+[[input.y:10.19: warning: stray '$'
+input.y:10.23: warning: stray '@'
+input.y:11.19: warning: stray '$'
+input.y:11.23: warning: stray '@'
+input.y:12.19: warning: stray '$'
+input.y:12.23: warning: stray '@'
+input.y:14.19: warning: stray '$'
+input.y:14.23: warning: stray '@'
+]])
+
+AT_CLEANUP
+
+
+
 ## ---------------- ##
 ## Code injection.  ##
 ## ---------------- ##