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/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_ */