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.
2026-03-09 12:23:04 +00:00 · 2006-07-29 05:53:42 +00:00
parent 868d2d9638
commit ec5479ce35
12 changed files with 771 additions and 276 deletions
--- a/44
+++ b/44
@@ -1,3 +1,47 @@
+2006-07-29  Joel E. Denny  <jdenny@ces.clemson.edu>
+
+	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.
+
 2006-07-29  Joel E. Denny  <jdenny@ces.clemson.edu>

 	Clean up handling of %destructor for the end token (token 0).
--- a/17
+++ b/17
@@ -12,6 +12,23 @@ Changes in version 2.3+:
 * Locations columns and lines start at 1.
  In accordance with the GNU Coding Standards and Emacs.

+* You may now declare a default %destructor and %printer:
+
+  For example:
+
+     %union { char *string; }
+     %token <string> STRING1
+     %token <string> STRING2
+     %type  <string> string1
+     %type  <string> string2
+     %destructor { free ($$); }
+     %destructor { free ($$); printf ("%d", @$.first_line); } STRING1 string1
+
+  guarantees that, when the parser discards any user-declared symbol, it passes
+  its semantic value to `free'.  However, when the parser discards a `STRING1'
+  or a `string1', it also prints its line number to `stdout'.  It performs only
+  the second `%destructor' in this case, so it invokes `free' only once.
+
 * Except for LALR(1) parsers in C with POSIX Yacc emulation enabled (with `-y',
  `--yacc', or `%yacc'), Bison no longer generates #define statements for
  associating token numbers with token names.  Removing the #define statements
--- a/doc/bison.texinfo
+++ b/doc/bison.texinfo
@@ -3348,8 +3348,8 @@ it might discard the previous semantic context @code{$<context>5} without
 restoring it.
 Thus, @code{$<context>5} needs a destructor (@pxref{Destructor Decl, , Freeing
 Discarded Symbols}).
-However, Bison currently provides no means to declare a destructor for a
-mid-rule action's semantic value.
+However, Bison currently provides no means to declare a destructor specific to
+a particular mid-rule action's semantic value.

 One solution is to bury the mid-rule action inside a nonterminal symbol and to
 declare a destructor for that symbol:
@@ -4007,26 +4007,40 @@ symbol is automatically discarded.
 Invoke the braced @var{code} whenever the parser discards one of the
@var{symbols}.
 Within @var{code}, @code{$$} designates the semantic value associated
-with the discarded symbol.  The additional parser parameters are also
-available (@pxref{Parser Function, , The Parser Function
-@code{yyparse}}).
+with the discarded symbol, and @code{@@$} designates its location.
+The additional parser parameters are also available (@pxref{Parser Function, ,
+The Parser Function @code{yyparse}}).
+@end deffn
+
+@deffn {Directive} %destructor @{ @var{code} @}
+@cindex default %destructor
+Invoke the braced @var{code} whenever the parser discards any user-declared
+grammar symbol for which the user has not specifically declared any
+@code{%destructor}.
+This is known as the default @code{%destructor}.
+As in the previous form, @code{$$}, @code{@@$}, and the additional parser
+parameters are available.
@end deffn

 For instance:

@smallexample
-%union
-@{
-  char *string;
-@}
-%token <string> STRING
-%type  <string> string
-%destructor @{ free ($$); @} STRING string
+%union @{ char *string; @}
+%token <string> STRING1
+%token <string> STRING2
+%type  <string> string1
+%type  <string> string2
+%destructor @{ free ($$); @}
+%destructor @{ free ($$); printf ("%d", @@$.first_line); @} STRING1 string1
@end smallexample

@noindent
-guarantees that when a @code{STRING} or a @code{string} is discarded,
-its associated memory will be freed.
+guarantees that, when the parser discards any user-declared symbol, it passes
+its semantic value to @code{free}.
+However, when the parser discards a @code{STRING1} or a @code{string1}, it also
+prints its line number to @code{stdout}.
+It performs only the second @code{%destructor} in this case, so it invokes
+@code{free} only once.

@sp 1

--- a/src/output.c
+++ b/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);
--- a/src/parse-gram.c
+++ b/src/parse-gram.c
--- a/src/parse-gram.h
+++ b/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
--- a/src/parse-gram.y
+++ b/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;
--- a/src/reader.c
+++ b/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));
 }

--- a/src/symtab.c
+++ b/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;
+}
--- a/src/symtab.h
+++ b/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_ */
--- a/tests/actions.at
+++ b/tests/actions.at
@@ -575,3 +575,202 @@ AT_CHECK_PRINTER_AND_DESTRUCTOR([%defines %skeleton "lalr1.cc"], [with union])

 AT_CHECK_PRINTER_AND_DESTRUCTOR([%glr-parser])
 AT_CHECK_PRINTER_AND_DESTRUCTOR([%glr-parser], [with union])
+
+
+
+
+
+## --------------------------------- ##
+## Default %printer and %destructor. ##
+## --------------------------------- ##
+
+# Check that the right %printer and %destructor are called, that they're not
+# called for $end, and that $$ and @$ work correctly.
+
+AT_SETUP([Default %printer and %destructor])
+
+AT_DATA_GRAMMAR([[input.y]],
+[[%error-verbose
+%debug
+%locations
+%initial-action {
+  @$.first_line = @$.last_line = 1;
+  @$.first_column = @$.last_column = 1;
+}
+
+%{
+# include <stdio.h>
+# include <stdlib.h>
+  static void yyerror (const char *msg);
+  static int yylex (void);
+# define USE(SYM)
+%}
+
+%printer {
+  fprintf (yyoutput, "Default printer for '%c' @ %d", $$, @$.first_column);
+}
+%destructor {
+  fprintf (stdout, "Default destructor for '%c' @ %d.\n", $$, @$.first_column);
+}
+
+%printer {
+  fprintf (yyoutput, "'b'/'c' printer for '%c' @ %d", $$, @$.first_column);
+} 'b' 'c'
+%destructor {
+  fprintf (stdout, "'b'/'c' destructor for '%c' @ %d.\n", $$, @$.first_column);
+} 'b' 'c'
+
+%%
+
+start: 'a' 'b' 'c' 'd' 'e' { $$ = 'S'; USE(($1, $2, $3, $4, $5)); } ;
+
+%%
+
+static int
+yylex (void)
+{
+  static const char *input = "abcd";
+  static int column = 1;
+  yylval = *input++;
+  yylloc.first_line = yylloc.last_line = 1;
+  yylloc.first_column = yylloc.last_column = column++;
+  return yylval;
+}
+
+static void
+yyerror (const char *msg)
+{
+  fprintf (stderr, "%s\n", msg);
+}
+
+int
+main (void)
+{
+  yydebug = 1;
+  return yyparse ();
+}
+]])
+
+AT_CHECK([bison -o input.c input.y])
+AT_COMPILE([input])
+AT_PARSER_CHECK([./input], 1,
+[[Default destructor for 'd' @ 4.
+'b'/'c' destructor for 'c' @ 3.
+'b'/'c' destructor for 'b' @ 2.
+Default destructor for 'a' @ 1.
+]],
+[[Starting parse
+Entering state 0
+Reading a token: Next token is token 'a' (1.1-1.1: Default printer for 'a' @ 1)
+Shifting token 'a' (1.1-1.1: Default printer for 'a' @ 1)
+Entering state 1
+Reading a token: Next token is token 'b' (1.2-1.2: 'b'/'c' printer for 'b' @ 2)
+Shifting token 'b' (1.2-1.2: 'b'/'c' printer for 'b' @ 2)
+Entering state 3
+Reading a token: Next token is token 'c' (1.3-1.3: 'b'/'c' printer for 'c' @ 3)
+Shifting token 'c' (1.3-1.3: 'b'/'c' printer for 'c' @ 3)
+Entering state 5
+Reading a token: Next token is token 'd' (1.4-1.4: Default printer for 'd' @ 4)
+Shifting token 'd' (1.4-1.4: Default printer for 'd' @ 4)
+Entering state 6
+Reading a token: Now at end of input.
+syntax error, unexpected $end, expecting 'e'
+Error: popping token 'd' (1.4-1.4: Default printer for 'd' @ 4)
+Stack now 0 1 3 5
+Error: popping token 'c' (1.3-1.3: 'b'/'c' printer for 'c' @ 3)
+Stack now 0 1 3
+Error: popping token 'b' (1.2-1.2: 'b'/'c' printer for 'b' @ 2)
+Stack now 0 1
+Error: popping token 'a' (1.1-1.1: Default printer for 'a' @ 1)
+Stack now 0
+Cleanup: discarding lookahead token $end (1.5-1.5: )
+Stack now 0
+]])
+
+AT_CLEANUP
+
+
+
+
+
+## ------------------------------------------------------------- ##
+## Default %printer and %destructor for user-declared end token. ##
+## ------------------------------------------------------------- ##
+
+AT_SETUP([Default %printer and %destructor for user-declared end token])
+
+AT_DATA_GRAMMAR([[input.y]],
+[[%error-verbose
+%debug
+%locations
+%initial-action {
+  @$.first_line = @$.last_line = 1;
+  @$.first_column = @$.last_column = 1;
+}
+
+%{
+# include <stdio.h>
+# include <stdlib.h>
+  static void yyerror (const char *msg);
+  static int yylex (void);
+# define USE(SYM)
+%}
+
+%token END 0
+%printer {
+  fprintf (yyoutput, "Default printer for '%c' @ %d", $$, @$.first_column);
+}
+%destructor {
+  fprintf (stdout, "Default destructor for '%c' @ %d.\n", $$, @$.first_column);
+}
+
+%%
+
+start: { $$ = 'S'; } ;
+
+%%
+
+static int
+yylex (void)
+{
+  yylval = 'E';
+  yylloc.first_line = yylloc.last_line = 1;
+  yylloc.first_column = yylloc.last_column = 1;
+  return 0;
+}
+
+static void
+yyerror (const char *msg)
+{
+  fprintf (stderr, "%s\n", msg);
+}
+
+int
+main (void)
+{
+  yydebug = 1;
+  return yyparse ();
+}
+]])
+
+AT_CHECK([bison -o input.c input.y])
+AT_COMPILE([input])
+AT_PARSER_CHECK([./input], 0,
+[[Default destructor for 'E' @ 1.
+Default destructor for 'S' @ 1.
+]],
+[[Starting parse
+Entering state 0
+Reducing stack by rule 1 (line 37):
+-> $$ = nterm start (1.1-1.1: Default printer for 'S' @ 1)
+Stack now 0
+Entering state 1
+Reading a token: Now at end of input.
+Shifting token END (1.1-1.1: Default printer for 'E' @ 1)
+Entering state 2
+Stack now 0 1 2
+Cleanup: popping token END (1.1-1.1: Default printer for 'E' @ 1)
+Cleanup: popping nterm start (1.1-1.1: Default printer for 'S' @ 1)
+]])
+
+AT_CLEANUP
--- a/tests/input.at
+++ b/tests/input.at
@@ -168,6 +168,65 @@ AT_CHECK_UNUSED_VALUES([1])
 AT_CLEANUP


+## --------------------------------------------- ##
+## Default %printer and %destructor redeclared.  ##
+## --------------------------------------------- ##
+
+AT_SETUP([Default %printer and %destructor redeclared])
+
+AT_DATA([[input.y]],
+[[%destructor { destroy ($$); }
+%printer { destroy ($$); }
+
+%destructor { destroy ($$); }
+%printer { destroy ($$); }
+
+%%
+
+start: ;
+
+%destructor { destroy ($$); };
+%printer { destroy ($$); };
+]])
+
+AT_CHECK([bison input.y], [1], [],
+[[input.y:4.13-29: redeclaration for default %destructor
+input.y:1.13-29: previous declaration
+input.y:5.10-26: redeclaration for default %printer
+input.y:2.10-26: previous declaration
+input.y:11.13-29: redeclaration for default %destructor
+input.y:4.13-29: previous declaration
+input.y:12.10-26: redeclaration for default %printer
+input.y:5.10-26: previous declaration
+]])
+
+AT_CLEANUP
+
+
+## ---------------------------------------- ##
+## Unused values with default %destructor.  ##
+## ---------------------------------------- ##
+
+AT_SETUP([Unused values with default %destructor])
+
+AT_DATA([[input.y]],
+[[%destructor { destroy ($$); }
+
+%%
+
+start: end end { $1; } ;
+end: { }  ;
+]])
+
+AT_CHECK([bison input.y], [0], [],
+[[input.y:5.8-22: warning: unset value: $$
+input.y:5.8-22: warning: unused value: $2
+input.y:6.6-8: warning: unset value: $$
+]])
+
+AT_CLEANUP
+
+
 ## ---------------------- ##
 ## Incompatible Aliases.  ##
 ## ---------------------- ##