Enable declaration of default %printer/%destructor. Make the parser

use these for all user-declared grammar symbols for which the user does
not declare a specific %printer/%destructor.  Thus, the parser uses it
for token 0 if the user declares it but not if Bison generates it as
$end.  Discussed starting at
<http://lists.gnu.org/archive/html/bison-patches/2006-02/msg00064.html>,
<http://lists.gnu.org/archive/html/bison-patches/2006-06/msg00091.html>,
and
<http://lists.gnu.org/archive/html/bison-patches/2006-07/msg00019.html>.
* NEWS (2.3+): Mention.
* doc/bison.texinfo (Actions in Mid-Rule): It's no longer impossible to
declare a %destructor for a mid-rule's semantic value.  It's just
impossible to declare one specific to it.
(Freeing Discarded Symbols): Mention that @$ can be used in %destructor
code.  Describe default %destructor form.
* src/parse-gram.y (grammar_declaration): Parse default
%printer/%destructor declarations.
* src/output.c (symbol_destructors_output): Use symbol_destructor_get
and symbol_destructor_location_get rather than accessing the destructor
and destructor_location members of struct symbol.
(symbol_printers_output): Likewise but for %printer's.
* src/reader.c (symbol_should_be_used): Likewise but for %destructor's
again.
* src/symtab.c (default_destructor, default_destructor_location,
default_printer, default_printer_location): New static global
variables to record the default %destructor and %printer.
(symbol_destructor_get, symbol_destructor_location_get,
symbol_printer_get, symbol_printer_location_get): New functions to
compute the appropriate %destructor and %printer for a symbol.
(default_destructor_set, default_printer_set): New functions to set the
default %destructor and %printer.
* src/symtab.h: Prototype all those new functions.
* tests/actions.at (Default %printer and %destructor): New test to
check that the right %printer and %destructor are called, that they're
not called for $end, and that $$ and @$ work correctly.
(Default %printer and %destructor for user-declared end token): New
test to check that the default %printer and %destructor are called for
a user-declared end token.
* tests/input.at (Default %printer and %destructor redeclared, Unused
values with default %destructor): New tests to check related grammar
warnings and errors.

src/output.c

@@ -390,7 +390,7 @@ symbol_destructors_output (FILE *out)
 
   fputs ("m4_define([b4_symbol_destructors], \n[", out);
   for (i = 0; i < nsyms; ++i)
-    if (symbols[i]->destructor)
+    if (symbol_destructor_get (symbols[i]))
       {
 	symbol *sym = symbols[i];
 
@@ -399,10 +399,12 @@ symbol_destructors_output (FILE *out)
 	   destructor, optional typename.  */
 	fprintf (out, "%s[", sep);
 	sep = ",\n";
-	escaped_output (out, sym->destructor_location.start.file);
-	fprintf (out, ", %d, ", sym->destructor_location.start.line);
+	escaped_output (out, symbol_destructor_location_get (sym).start.file);
+	fprintf (out, ", %d, ",
+		 symbol_destructor_location_get (sym).start.line);
 	escaped_output (out, sym->tag);
-	fprintf (out, ", %d, [[%s]]", sym->number, sym->destructor);
+	fprintf (out, ", %d, [[%s]]", sym->number,
+		 symbol_destructor_get (sym));
 	if (sym->type_name)
 	  fprintf (out, ", [[%s]]", sym->type_name);
 	fputc (']', out);
@@ -423,7 +425,7 @@ symbol_printers_output (FILE *out)
 
   fputs ("m4_define([b4_symbol_printers], \n[", out);
   for (i = 0; i < nsyms; ++i)
-    if (symbols[i]->printer)
+    if (symbol_printer_get (symbols[i]))
       {
 	symbol *sym = symbols[i];
 
@@ -432,10 +434,10 @@ symbol_printers_output (FILE *out)
 	   printer, optional typename.  */
 	fprintf (out, "%s[", sep);
 	sep = ",\n";
-	escaped_output (out, sym->printer_location.start.file);
-	fprintf (out, ", %d, ", sym->printer_location.start.line);
+	escaped_output (out, symbol_printer_location_get (sym).start.file);
+	fprintf (out, ", %d, ", symbol_printer_location_get (sym).start.line);
 	escaped_output (out, sym->tag);
-	fprintf (out, ", %d, [[%s]]", sym->number, sym->printer);
+	fprintf (out, ", %d, [[%s]]", sym->number, symbol_printer_get (sym));
 	if (sym->type_name)
 	  fprintf (out, ", [[%s]]", sym->type_name);
 	fputc (']', out);

src/parse-gram.h

@@ -159,7 +159,7 @@
 
 #if ! defined YYSTYPE && ! defined YYSTYPE_IS_DECLARED
 typedef union YYSTYPE
-{/* Line 1539 of yacc.c.  */
+{/* Line 1535 of yacc.c.  */
 #line 97 "parse-gram.y"
 
   symbol *symbol;
@@ -170,7 +170,7 @@ typedef union YYSTYPE
   uniqstr uniqstr;
   unsigned char character;
 }
-/* Line 1539 of yacc.c.  */
+/* Line 1535 of yacc.c.  */
 #line 175 "parse-gram.h"
 	YYSTYPE;
 # define YYSTYPE_IS_TRIVIAL 1

src/parse-gram.y

@@ -261,6 +261,10 @@ grammar_declaration:
     {
       grammar_start_symbol_set ($2, @2);
     }
+| "%destructor" "{...}"
+    {
+      default_destructor_set (translate_symbol_action ($2, @2), @2);
+    }
 | "%destructor" "{...}" symbols.1
     {
       symbol_list *list;
@@ -277,6 +281,10 @@ grammar_declaration:
 	symbol_printer_set (list->sym, action, @2);
       symbol_list_free ($3);
     }
+| "%printer" "{...}"
+    {
+      default_printer_set (translate_symbol_action ($2, @2), @2);
+    }
 | "%default-prec"
     {
       default_prec = true;

src/reader.c

@@ -259,7 +259,7 @@ grammar_current_rule_begin (symbol *lhs, location loc)
 static bool
 symbol_should_be_used (symbol_list const *s)
 {
-  return (s->sym->destructor
+  return (symbol_destructor_get (s->sym)
 	  || (s->midrule && s->midrule->used));
 }
 

src/symtab.c

@@ -41,6 +41,15 @@ symbol *accept = NULL;
 symbol *startsymbol = NULL;
 location startsymbol_location;
 
+/*-----------------------------------.
+| Default %destructor and %printer.  |
+`-----------------------------------*/
+
+static const char *default_destructor = NULL;
+static location default_destructor_location;
+static const char *default_printer = NULL;
+static location default_printer_location;
+
 /*---------------------------------.
 | Create a new symbol, named TAG.  |
 `---------------------------------*/
@@ -147,6 +156,33 @@ symbol_destructor_set (symbol *sym, const char *destructor, location loc)
     }
 }
 
+/*---------------------------------------.
+| Get the computed %destructor for SYM.  |
+`---------------------------------------*/
+
+const char *
+symbol_destructor_get (symbol *sym)
+{
+  /* Token 0 cannot have a %destructor unless the user renames it.  */
+  if (UNIQSTR_EQ (sym->tag, uniqstr_new ("$end")))
+    return NULL;
+
+  if (sym->destructor != NULL)
+    return sym->destructor;
+  return default_destructor;
+}
+
+/*---------------------------------------------------------------.
+| Get the grammar location of the %destructor computed for SYM.  |
+`---------------------------------------------------------------*/
+
+location
+symbol_destructor_location_get (symbol *sym)
+{
+  if (sym->destructor != NULL)
+    return sym->destructor_location;
+  return default_destructor_location;
+}
 
 /*---------------------------------------------------------------.
 | Set the PRINTER associated with SYM.  Do nothing if passed 0.  |
@@ -164,6 +200,34 @@ symbol_printer_set (symbol *sym, const char *printer, location loc)
     }
 }
 
+/*------------------------------------.
+| Get the computed %printer for SYM.  |
+`------------------------------------*/
+
+const char *
+symbol_printer_get (symbol *sym)
+{
+  /* Token 0 cannot have a %printer unless the user renames it.  */
+  if (UNIQSTR_EQ (sym->tag, uniqstr_new ("$end")))
+    return NULL;
+
+  if (sym->printer != NULL)
+    return sym->printer;
+  return default_printer;
+}
+
+/*------------------------------------------------------------.
+| Get the grammar location of the %printer computed for SYM.  |
+`------------------------------------------------------------*/
+
+location
+symbol_printer_location_get (symbol *sym)
+{
+  if (sym->printer != NULL)
+    return sym->printer_location;
+  return default_printer_location;
+}
+
 
 /*-----------------------------------------------------------------.
 | Set the PRECEDENCE associated with SYM.  Does nothing if invoked |
@@ -666,3 +730,32 @@ symbols_pack (void)
 	      _("the start symbol %s is a token"),
 	      startsymbol->tag);
 }
+
+
+/*-----------------------------------.
+| Set default %destructor/%printer.  |
+`-----------------------------------*/
+
+void
+default_destructor_set (const char *destructor, location loc)
+{
+  if (default_destructor != NULL)
+    {
+      complain_at (loc, _("redeclaration for default %%destructor"));
+      complain_at (default_destructor_location, _("previous declaration"));
+    }
+  default_destructor = destructor;
+  default_destructor_location = loc;
+}
+
+void
+default_printer_set (const char *printer, location loc)
+{
+  if (default_printer != NULL)
+    {
+      complain_at (loc, _("redeclaration for default %%printer"));
+      complain_at (default_printer_location, _("previous declaration"));
+    }
+  default_printer = printer;
+  default_printer_location = loc;
+}

src/symtab.h

@@ -61,16 +61,35 @@ struct symbol
   /** The location of its first occurrence.  */
   location location;
 
-  /** Its %type and associated printer and destructor.  */
+  /** Its \c \%type.  */
   uniqstr type_name;
+  /** Its \c \%type's location.  */
   location type_location;
 
-  /** Does not own the memory. */
+  /** Any \c \%destructor declared specifically for this symbol.
+
+     Access this field only through <tt>symbol</tt>'s interface functions.  For
+     example, if <tt>symbol::destructor = NULL</tt>, the default
+     \c \%destructor or a per-type \c \%destructor might be appropriate, and
+     \c symbol_destructor_get will compute the correct one.  */
   const char *destructor;
+
+  /** The location of \c symbol::destructor.
+
+     Access this field only through <tt>symbol</tt>'s interface functions.
+     \sa symbol::destructor  */
   location destructor_location;
 
-  /** Printer. */
+  /** Any \c \%printer declared specifically for this symbol.
+
+     Access this field only through <tt>symbol</tt>'s interface functions.
+     \sa symbol::destructor  */
   const char *printer;
+
+  /** The location of \c symbol::printer.
+
+     Access this field only through <tt>symbol</tt>'s interface functions.
+     \sa symbol::destructor  */
   location printer_location;
 
   symbol_number number;
@@ -125,9 +144,25 @@ void symbol_type_set (symbol *sym, uniqstr type_name, location loc);
 /** Set the \c destructor associated with \c sym.  */
 void symbol_destructor_set (symbol *sym, const char *destructor, location loc);
 
+/** Get the computed \c \%destructor for \c sym, or \c NULL if none.   */
+const char *symbol_destructor_get (symbol *sym);
+
+/** Get the grammar location of the computed \c \%destructor for \c sym.
+ 
+  \pre <tt>symbol_destructor_get (sym) != NULL</tt> */
+location symbol_destructor_location_get (symbol *sym);
+
 /** Set the \c printer associated with \c sym.  */
 void symbol_printer_set (symbol *sym, const char *printer, location loc);
 
+/** Get the computed \c \%printer for \c sym, or \c NULL if none.  */
+const char *symbol_printer_get (symbol *sym);
+
+/** Get the grammar location of the computed \c \%printer for \c sym.
+
+  \pre <tt>symbol_printer_get (sym) != NULL</tt> */
+location symbol_printer_location_get (symbol *sym);
+
 /* Set the \c precedence associated with \c sym.
 
    Ensure that \a symbol is a terminal.
@@ -155,7 +190,7 @@ extern symbol *accept;
 
 /** The user start symbol. */
 extern symbol *startsymbol;
-/** The location of the \c %start declaration.  */
+/** The location of the \c \%start declaration.  */
 extern location startsymbol_location;
 
 
@@ -181,4 +216,15 @@ void symbols_check_defined (void);
    #token_translations.  */
 void symbols_pack (void);
 
+
+/*-----------------------------------.
+| Default %destructor and %printer.  |
+`-----------------------------------*/
+
+/** Set the default \c \%destructor.  */
+void default_destructor_set (const char *destructor, location loc);
+
+/** Set the default \c \%printer.  */
+void default_printer_set (const char *printer, location loc);
+
 #endif /* !SYMTAB_H_ */