graphs: add tests, introducing -k graph

[bison.git] / tests / actions.at

# Executing Actions.                               -*- Autotest -*-

# Copyright (C) 2001-2012 Free Software Foundation, Inc.

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

AT_BANNER([[User Actions.]])

## ------------------ ##
## Mid-rule actions.  ##
## ------------------ ##

AT_SETUP([Mid-rule actions])

# Bison once forgot the mid-rule actions.  It was because the action
# was attached to the host rule (the one with the mid-rule action),
# instead of being attached to the empty rule dedicated to this
# action.

AT_BISON_OPTION_PUSHDEFS
AT_DATA_GRAMMAR([[input.y]],
[[%error-verbose
%debug
%{
]AT_YYERROR_DECLARE[
]AT_YYLEX_DECLARE[
%}
%%
exp:     { putchar ('0'); }
     '1' { putchar ('1'); }
     '2' { putchar ('2'); }
     '3' { putchar ('3'); }
     '4' { putchar ('4'); }
     '5' { putchar ('5'); }
     '6' { putchar ('6'); }
     '7' { putchar ('7'); }
     '8' { putchar ('8'); }
     '9' { putchar ('9'); }
         { putchar ('\n'); }
   ;
%%
]AT_YYERROR_DEFINE[
]AT_YYLEX_DEFINE(["123456789"])[
int
main (void)
{
  return yyparse ();
}
]])
AT_BISON_OPTION_POPDEFS

AT_BISON_CHECK([-d -v -o input.c input.y])
AT_COMPILE([input])
AT_PARSER_CHECK([./input], 0,
[[0123456789
]])

AT_CLEANUP





## ---------------- ##
## Exotic Dollars.  ##
## ---------------- ##

AT_SETUP([Exotic Dollars])

AT_BISON_OPTION_PUSHDEFS
AT_DATA_GRAMMAR([[input.y]],
[[%error-verbose
%debug
%{
]AT_YYERROR_DECLARE[
]AT_YYLEX_DECLARE[
# define USE(Var)
%}

%union
{
  int val;
};

%type <val> a_1 a_2 a_5
            sum_of_the_five_previous_values

%%
exp: a_1 a_2 { $<val>$ = 3; } { $<val>$ = $<val>3 + 1; } a_5
     sum_of_the_five_previous_values
    {
       USE (($1, $2, $<foo>3, $<foo>4, $5));
       printf ("%d\n", $6);
    }
;
a_1: { $$ = 1; };
a_2: { $$ = 2; };
a_5: { $$ = 5; };

sum_of_the_five_previous_values:
    {
       $$ = $<val>0 + $<val>-1 + $<val>-2 + $<val>-3 + $<val>-4;
    }
;

%%
]AT_YYERROR_DEFINE[
]AT_YYLEX_DEFINE[
int
main (void)
{
  return yyparse ();
}
]])

AT_BISON_CHECK([-d -v -o input.c input.y], 0)
AT_COMPILE([input])
AT_PARSER_CHECK([./input], 0,
[[15
]])

# Make sure that fields after $n or $-n are parsed correctly.  At one
# point while implementing dashes in symbol names, we were dropping
# fields after $-n.
AT_DATA_GRAMMAR([[input.y]],
[[
%{
#include <stdio.h>
]AT_YYERROR_DECLARE[
]AT_YYLEX_DECLARE[
  typedef struct { int val; } stype;
# define YYSTYPE stype
%}

%%
start: one two { $$.val = $1.val + $2.val; } sum ;
one: { $$.val = 1; } ;
two: { $$.val = 2; } ;
sum: { printf ("%d\n", $0.val + $-1.val + $-2.val); } ;

%%
]AT_YYERROR_DEFINE[
]AT_YYLEX_DEFINE[
int
main (void)
{
  return yyparse ();
}
]])

AT_BISON_CHECK([[-o input.c input.y]])
AT_COMPILE([[input]])
AT_PARSER_CHECK([[./input]], [[0]],
[[6
]])

AT_BISON_OPTION_POPDEFS
AT_CLEANUP



## -------------------------- ##
## Printers and Destructors.  ##
## -------------------------- ##

# _AT_CHECK_PRINTER_AND_DESTRUCTOR($1, $2, $3, $4,
#                                  BISON-DIRECTIVE, UNION-FLAG)
# -------------------------------------------------------------
m4_define([_AT_CHECK_PRINTER_AND_DESTRUCTOR],
[# Make sure complex $n work.
m4_if([$1$2$3$4], $[1]$[2]$[3]$[4], [],
       [m4_fatal([$0: Invalid arguments: $@])])dnl

# Be sure to pass all the %directives to this macro to have correct
# helping macros.  So don't put any directly in the Bison file.
AT_BISON_OPTION_PUSHDEFS([$5])
AT_DATA_GRAMMAR([[input.y]],
[[%code requires {
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#define YYINITDEPTH 10
#define YYMAXDEPTH 10
#define RANGE(Location) ]AT_LALR1_CC_IF([(Location).begin.line, (Location).end.line],
      [(Location).first_line, (Location).last_line])[

/* Display the symbol type Symbol.  */
#define V(Symbol, Value, Location, Sep) \
   fprintf (stderr, #Symbol " (%d@%d-%d)" Sep, Value, RANGE(Location))
}

$5
]m4_ifval([$6], [%union
{
  int ival;
}])
AT_LALR1_CC_IF([%define global_tokens_and_yystype])
m4_ifval([$6], [[%code provides {]], [[%code {]])
AT_LALR1_CC_IF([typedef yy::location YYLTYPE;])[
]AT_YYLEX_DECLARE[
]AT_LALR1_CC_IF([], [AT_YYERROR_DECLARE])
[}

]m4_ifval([$6], [%type <ival> '(' 'x' 'y' ')' ';' thing line input END])[

/* FIXME: This %printer isn't actually tested.  */
%printer
  {
    ]AT_LALR1_CC_IF([debug_stream () << $$;],
                    [fprintf (yyoutput, "%d", $$)])[;
  }
  input line thing 'x' 'y'

%destructor
  { fprintf (stderr, "Freeing nterm input (%d@%d-%d)\n", $$, RANGE (@$)); }
  input

%destructor
  { fprintf (stderr, "Freeing nterm line (%d@%d-%d)\n", $$, RANGE (@$)); }
  line

%destructor
  { fprintf (stderr, "Freeing nterm thing (%d@%d-%d)\n", $$, RANGE (@$)); }
  thing

%destructor
  { fprintf (stderr, "Freeing token 'x' (%d@%d-%d)\n", $$, RANGE (@$)); }
  'x'

%destructor
  { fprintf (stderr, "Freeing token 'y' (%d@%d-%d)\n", $$, RANGE (@$)); }
  'y'

%token END 0
%destructor
  { fprintf (stderr, "Freeing token END (%d@%d-%d)\n", $$, RANGE (@$)); }
  END

%%
/*
   This grammar is made to exercise error recovery.
   "Lines" starting with `(' support error recovery, with
   ')' as synchronizing token.  Lines starting with 'x' can never
   be recovered from if in error.
*/

input:
  /* Nothing. */
    {
      $$ = 0;
      V(input, $$, @$, ": /* Nothing */\n");
    }
| line input /* Right recursive to load the stack so that popping at
		END can	be exercised.  */
    {
      $$ = 2;
      V(input, $$, @$, ": ");
      V(line,  $1, @1, " ");
      V(input, $2, @2, "\n");
    }
;

line:
  thing thing thing ';'
    {
      $$ = $1;
      V(line,  $$, @$, ": ");
      V(thing, $1, @1, " ");
      V(thing, $2, @2, " ");
      V(thing, $3, @3, " ");
      V(;,     $4, @4, "\n");
    }
| '(' thing thing ')'
    {
      $$ = $1;
      V(line,  $$, @$, ": ");
      V('(',   $1, @1, " ");
      V(thing, $2, @2, " ");
      V(thing, $3, @3, " ");
      V(')',   $4, @4, "\n");
    }
| '(' thing ')'
    {
      $$ = $1;
      V(line,  $$, @$, ": ");
      V('(',   $1, @1, " ");
      V(thing, $2, @2, " ");
      V(')',   $3, @3, "\n");
    }
| '(' error ')'
    {
      $$ = -1;
      V(line,  $$, @$, ": ");
      V('(',   $1, @1, " ");
      fprintf (stderr, "error (@%d-%d) ", RANGE(@2));
      V(')',   $3, @3, "\n");
    }
;

thing:
  'x'
    {
      $$ = $1;
      V(thing, $$, @$, ": ");
      V('x',   $1, @1, "\n");
    }
;
%%
/* Alias to ARGV[1]. */
const char *source = YY_NULL;

]AT_YYERROR_DEFINE[

static
]AT_YYLEX_PROTOTYPE[
{
  static unsigned int counter = 0;

  int c = ]AT_VAL[]m4_ifval([$6], [.ival])[ = counter++;
  /* As in BASIC, line numbers go from 10 to 10.  */
  ]AT_LOC_FIRST_LINE[ = ]AT_LOC_FIRST_COLUMN[ = 10 * c;
  ]AT_LOC_LAST_LINE[ = ]AT_LOC_LAST_COLUMN[ = ]AT_LOC_FIRST_LINE[ + 9;
  assert (0 <= c && c <= strlen (source));
  if (source[c])
    fprintf (stderr, "sending: '%c'", source[c]);
  else
    fprintf (stderr, "sending: END");
  fprintf (stderr, " (%d@%d-%d)\n", c, RANGE (]AT_LOC[));
  return source[c];
}
]AT_LALR1_CC_IF(
[static bool yydebug;
int
yyparse ()
{
  yy::parser parser;
  parser.set_debug_level (yydebug);
  return parser.parse ();
}
])[

int
main (int argc, const char *argv[])
{
  int status;
  yydebug = !!getenv ("YYDEBUG");
  assert (argc == 2);
  source = argv[1];
  status = yyparse ();
  switch (status)
    {
      case 0: fprintf (stderr, "Successful parse.\n"); break;
      case 1: fprintf (stderr, "Parsing FAILED.\n"); break;
      default: fprintf (stderr, "Parsing FAILED (status %d).\n", status); break;
    }
  return status;
}
]])

AT_FULL_COMPILE([input])


# Check the location of "empty"
# -----------------------------
# I.e., epsilon-reductions, as in "(x)" which ends by reducing
# an empty "line" nterm.
# FIXME: This location is not satisfying.  Depend on the lookahead?
AT_PARSER_CHECK([./input '(x)'], 0, [],
[[sending: '(' (0@0-9)
sending: 'x' (1@10-19)
thing (1@10-19): 'x' (1@10-19)
sending: ')' (2@20-29)
line (0@0-29): '(' (0@0-9) thing (1@10-19) ')' (2@20-29)
sending: END (3@30-39)
input (0@29-29): /* Nothing */
input (2@0-29): line (0@0-29) input (0@29-29)
Freeing token END (3@30-39)
Freeing nterm input (2@0-29)
Successful parse.
]])


# Check locations in error recovery
# ---------------------------------
# '(y)' is an error, but can be recovered from.  But what's the location
# of the error itself ('y'), and of the resulting reduction ('(error)').
AT_PARSER_CHECK([./input '(y)'], 0, [],
[[sending: '(' (0@0-9)
sending: 'y' (1@10-19)
10.10-19.18: syntax error, unexpected 'y', expecting 'x'
Freeing token 'y' (1@10-19)
sending: ')' (2@20-29)
line (-1@0-29): '(' (0@0-9) error (@10-19) ')' (2@20-29)
sending: END (3@30-39)
input (0@29-29): /* Nothing */
input (2@0-29): line (-1@0-29) input (0@29-29)
Freeing token END (3@30-39)
Freeing nterm input (2@0-29)
Successful parse.
]])


# Syntax errors caught by the parser
# ----------------------------------
# Exercise the discarding of stack top and input until `error'
# can be reduced.
#
#     '(', 'x', 'x', 'x', 'x', 'x', ')',
#
# Load the stack and provoke an error that cannot be caught by the
# grammar, to check that the stack is cleared.  And make sure the
# lookahead is freed.
#
#     '(', 'x', ')',
#     '(', 'x', ')',
#     'y'
AT_PARSER_CHECK([./input '(xxxxx)(x)(x)y'], 1, [],
[[sending: '(' (0@0-9)
sending: 'x' (1@10-19)
thing (1@10-19): 'x' (1@10-19)
sending: 'x' (2@20-29)
thing (2@20-29): 'x' (2@20-29)
sending: 'x' (3@30-39)
30.30-39.38: syntax error, unexpected 'x', expecting ')'
Freeing nterm thing (2@20-29)
Freeing nterm thing (1@10-19)
Freeing token 'x' (3@30-39)
sending: 'x' (4@40-49)
Freeing token 'x' (4@40-49)
sending: 'x' (5@50-59)
Freeing token 'x' (5@50-59)
sending: ')' (6@60-69)
line (-1@0-69): '(' (0@0-9) error (@10-59) ')' (6@60-69)
sending: '(' (7@70-79)
sending: 'x' (8@80-89)
thing (8@80-89): 'x' (8@80-89)
sending: ')' (9@90-99)
line (7@70-99): '(' (7@70-79) thing (8@80-89) ')' (9@90-99)
sending: '(' (10@100-109)
sending: 'x' (11@110-119)
thing (11@110-119): 'x' (11@110-119)
sending: ')' (12@120-129)
line (10@100-129): '(' (10@100-109) thing (11@110-119) ')' (12@120-129)
sending: 'y' (13@130-139)
input (0@129-129): /* Nothing */
input (2@100-129): line (10@100-129) input (0@129-129)
input (2@70-129): line (7@70-99) input (2@100-129)
input (2@0-129): line (-1@0-69) input (2@70-129)
130.130-139.138: syntax error, unexpected 'y', expecting END
Freeing nterm input (2@0-129)
Freeing token 'y' (13@130-139)
Parsing FAILED.
]])


# Syntax error caught by the parser where lookahead = END
# --------------------------------------------------------
# Load the stack and provoke an error that cannot be caught by the
# grammar, to check that the stack is cleared.  And make sure the
# lookahead is freed.
#
#     '(', 'x', ')',
#     '(', 'x', ')',
#     'x'
AT_PARSER_CHECK([./input '(x)(x)x'], 1, [],
[[sending: '(' (0@0-9)
sending: 'x' (1@10-19)
thing (1@10-19): 'x' (1@10-19)
sending: ')' (2@20-29)
line (0@0-29): '(' (0@0-9) thing (1@10-19) ')' (2@20-29)
sending: '(' (3@30-39)
sending: 'x' (4@40-49)
thing (4@40-49): 'x' (4@40-49)
sending: ')' (5@50-59)
line (3@30-59): '(' (3@30-39) thing (4@40-49) ')' (5@50-59)
sending: 'x' (6@60-69)
thing (6@60-69): 'x' (6@60-69)
sending: END (7@70-79)
70.70-79.78: syntax error, unexpected END, expecting 'x'
Freeing nterm thing (6@60-69)
Freeing nterm line (3@30-59)
Freeing nterm line (0@0-29)
Freeing token END (7@70-79)
Parsing FAILED.
]])


# Check destruction upon stack overflow
# -------------------------------------
# Upon stack overflow, all symbols on the stack should be destroyed.
# Only check for yacc.c.
AT_YACC_IF([
AT_PARSER_CHECK([./input '(x)(x)(x)(x)(x)(x)(x)'], 2, [],
[[sending: '(' (0@0-9)
sending: 'x' (1@10-19)
thing (1@10-19): 'x' (1@10-19)
sending: ')' (2@20-29)
line (0@0-29): '(' (0@0-9) thing (1@10-19) ')' (2@20-29)
sending: '(' (3@30-39)
sending: 'x' (4@40-49)
thing (4@40-49): 'x' (4@40-49)
sending: ')' (5@50-59)
line (3@30-59): '(' (3@30-39) thing (4@40-49) ')' (5@50-59)
sending: '(' (6@60-69)
sending: 'x' (7@70-79)
thing (7@70-79): 'x' (7@70-79)
sending: ')' (8@80-89)
line (6@60-89): '(' (6@60-69) thing (7@70-79) ')' (8@80-89)
sending: '(' (9@90-99)
sending: 'x' (10@100-109)
thing (10@100-109): 'x' (10@100-109)
sending: ')' (11@110-119)
line (9@90-119): '(' (9@90-99) thing (10@100-109) ')' (11@110-119)
sending: '(' (12@120-129)
sending: 'x' (13@130-139)
thing (13@130-139): 'x' (13@130-139)
sending: ')' (14@140-149)
line (12@120-149): '(' (12@120-129) thing (13@130-139) ')' (14@140-149)
sending: '(' (15@150-159)
sending: 'x' (16@160-169)
thing (16@160-169): 'x' (16@160-169)
sending: ')' (17@170-179)
line (15@150-179): '(' (15@150-159) thing (16@160-169) ')' (17@170-179)
sending: '(' (18@180-189)
sending: 'x' (19@190-199)
thing (19@190-199): 'x' (19@190-199)
sending: ')' (20@200-209)
200.200-209.208: memory exhausted
Freeing nterm thing (19@190-199)
Freeing nterm line (15@150-179)
Freeing nterm line (12@120-149)
Freeing nterm line (9@90-119)
Freeing nterm line (6@60-89)
Freeing nterm line (3@30-59)
Freeing nterm line (0@0-29)
Parsing FAILED (status 2).
]])
])

AT_BISON_OPTION_POPDEFS
])# _AT_CHECK_PRINTER_AND_DESTRUCTOR


# AT_CHECK_PRINTER_AND_DESTRUCTOR([BISON-OPTIONS], [UNION-FLAG], [SKIP_FLAG])
# ---------------------------------------------------------------------------
m4_define([AT_CHECK_PRINTER_AND_DESTRUCTOR],
[AT_SETUP([Printers and Destructors $2: $1])

$3
_AT_CHECK_PRINTER_AND_DESTRUCTOR($[1], $[2], $[3], $[4],
[%error-verbose
%debug
%verbose
%locations
$1], [$2])

AT_CLEANUP
])


AT_CHECK_PRINTER_AND_DESTRUCTOR([])
AT_CHECK_PRINTER_AND_DESTRUCTOR([], [with union])

AT_CHECK_PRINTER_AND_DESTRUCTOR([%defines %skeleton "lalr1.cc"])
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 tagless %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 tagless %printer and %destructor])
AT_BISON_OPTION_PUSHDEFS([%locations])
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>
]AT_YYLEX_DECLARE[
]AT_YYERROR_DECLARE[
# define USE(SYM)
%}

%printer {
  fprintf (yyoutput, "<*> printer should not be called.\n");
} <*>

%printer {
  fprintf (yyoutput, "<> printer for '%c' @ %d", $$, @$.first_column);
} <>
%destructor {
  fprintf (stdout, "<> destructor for '%c' @ %d.\n", $$, @$.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'

%destructor {
  fprintf (yyoutput, "<*> destructor should not be called.\n");
} <*>

%%

start: 'a' 'b' 'c' 'd' 'e' { $$ = 'S'; USE(($1, $2, $3, $4, $5)); } ;

%%
]AT_YYERROR_DEFINE[
]AT_YYLEX_DEFINE(["abcd"], [[yylval = res]])[

int
main (void)
{
  yydebug = 1;
  return yyparse ();
}
]])

AT_BISON_CHECK([-o input.c input.y])
AT_COMPILE([input])
AT_PARSER_CHECK([./input], 1,
[[<> destructor for 'd' @ 4.
'b'/'c' destructor for 'c' @ 3.
'b'/'c' destructor for 'b' @ 2.
<> destructor for 'a' @ 1.
]],
[[Starting parse
Entering state 0
Reading a token: Next token is token 'a' (1.1-1.1: <> printer for 'a' @ 1)
Shifting token 'a' (1.1-1.1: <> 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: <> printer for 'd' @ 4)
Shifting token 'd' (1.4-1.4: <> printer for 'd' @ 4)
Entering state 6
Reading a token: Now at end of input.
1.5-4: syntax error, unexpected $end, expecting 'e'
Error: popping token 'd' (1.4-1.4: <> 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: <> printer for 'a' @ 1)
Stack now 0
Cleanup: discarding lookahead token $end (1.5-1.5: )
Stack now 0
]])

AT_BISON_OPTION_POPDEFS
AT_CLEANUP



## ------------------------------------------------------ ##
## Default tagged and per-type %printer and %destructor.  ##
## ------------------------------------------------------ ##

AT_SETUP([Default tagged and per-type %printer and %destructor])
AT_BISON_OPTION_PUSHDEFS
AT_DATA_GRAMMAR([[input.y]],
[[%error-verbose
%debug

%{
# include <stdio.h>
# include <stdlib.h>
]AT_YYERROR_DECLARE[
]AT_YYLEX_DECLARE[
# define USE(SYM)
%}

%printer {
  fprintf (yyoutput, "<> printer should not be called.\n");
} <>

%union { int field0; int field1; int field2; }
%type <field0> start 'a' 'g'
%type <field1> 'e'
%type <field2> 'f'
%printer {
  fprintf (yyoutput, "<*>/<field2>/e printer");
} <*> 'e' <field2>
%destructor {
  fprintf (stdout, "<*>/<field2>/e destructor.\n");
} <*> 'e' <field2>

%type <field1> 'b'
%printer { fprintf (yyoutput, "<field1> printer"); } <field1>
%destructor { fprintf (stdout, "<field1> destructor.\n"); } <field1>

%type <field0> 'c'
%printer { fprintf (yyoutput, "'c' printer"); } 'c'
%destructor { fprintf (stdout, "'c' destructor.\n"); } 'c'

%type <field1> 'd'
%printer { fprintf (yyoutput, "'d' printer"); } 'd'
%destructor { fprintf (stdout, "'d' destructor.\n"); } 'd'

%destructor {
  fprintf (yyoutput, "<> destructor should not be called.\n");
} <>

%%

start:
  'a' 'b' 'c' 'd' 'e' 'f' 'g'
    {
      USE(($1, $2, $3, $4, $5, $6, $7));
      $$ = 'S';
    }
  ;

%%
]AT_YYERROR_DEFINE[
]AT_YYLEX_DEFINE(["abcdef"])[

int
main (void)
{
  yydebug = 1;
  return yyparse ();
}
]])

AT_BISON_CHECK([-o input.c input.y])
AT_COMPILE([input])
AT_PARSER_CHECK([./input], 1,
[[<*>/<field2>/e destructor.
<*>/<field2>/e destructor.
'd' destructor.
'c' destructor.
<field1> destructor.
<*>/<field2>/e destructor.
]],
[[Starting parse
Entering state 0
Reading a token: Next token is token 'a' (<*>/<field2>/e printer)
Shifting token 'a' (<*>/<field2>/e printer)
Entering state 1
Reading a token: Next token is token 'b' (<field1> printer)
Shifting token 'b' (<field1> printer)
Entering state 3
Reading a token: Next token is token 'c' ('c' printer)
Shifting token 'c' ('c' printer)
Entering state 5
Reading a token: Next token is token 'd' ('d' printer)
Shifting token 'd' ('d' printer)
Entering state 6
Reading a token: Next token is token 'e' (<*>/<field2>/e printer)
Shifting token 'e' (<*>/<field2>/e printer)
Entering state 7
Reading a token: Next token is token 'f' (<*>/<field2>/e printer)
Shifting token 'f' (<*>/<field2>/e printer)
Entering state 8
Reading a token: Now at end of input.
syntax error, unexpected $end, expecting 'g'
Error: popping token 'f' (<*>/<field2>/e printer)
Stack now 0 1 3 5 6 7
Error: popping token 'e' (<*>/<field2>/e printer)
Stack now 0 1 3 5 6
Error: popping token 'd' ('d' printer)
Stack now 0 1 3 5
Error: popping token 'c' ('c' printer)
Stack now 0 1 3
Error: popping token 'b' (<field1> printer)
Stack now 0 1
Error: popping token 'a' (<*>/<field2>/e printer)
Stack now 0
Cleanup: discarding lookahead token $end ()
Stack now 0
]])

AT_BISON_OPTION_POPDEFS
AT_CLEANUP



## ------------------------------------------------------------- ##
## Default %printer and %destructor for user-defined end token.  ##
## ------------------------------------------------------------- ##

AT_SETUP([Default %printer and %destructor for user-defined end token])

# _AT_CHECK_DEFAULT_PRINTER_AND_DESTRUCTOR_FOR_END_TOKEN(TYPED)
# -------------------------------------------------------------
m4_define([_AT_CHECK_DEFAULT_PRINTER_AND_DESTRUCTOR_FOR_END_TOKEN],
[m4_if($1, 0,
  [m4_pushdef([kind], []) m4_pushdef([not_kind], [*])],
  [m4_pushdef([kind], [*]) m4_pushdef([not_kind], [])])

AT_BISON_OPTION_PUSHDEFS([%locations])
AT_DATA_GRAMMAR([[input]]$1[[.y]],
[[%error-verbose
%debug
%locations
%initial-action {
  @$.first_line = @$.last_line = 1;
  @$.first_column = @$.last_column = 1;
}

%{
# include <stdio.h>
# include <stdlib.h>
]AT_YYERROR_DECLARE[
]AT_YYLEX_DECLARE[
# define USE(SYM)
%}

%destructor {
  fprintf (yyoutput, "<]]not_kind[[> destructor should not be called.\n");
} <]]not_kind[[>

%token END 0
%printer {
  fprintf (yyoutput, "<]]kind[[> for '%c' @ %d", $$, @$.first_column);
} <]]kind[[>
%destructor {
  fprintf (stdout, "<]]kind[[> for '%c' @ %d.\n", $$, @$.first_column);
} <]]kind[[>

%printer {
  fprintf (yyoutput, "<]]not_kind[[> printer should not be called.\n");
} <]]not_kind[[>

]]m4_if($1, 0, [[[
]]],
[[[%union { char tag; }
%type <tag> start END]]])[[

%%

start: { $$ = 'S'; } ;

%%

static int
yylex (void)
{
  static int called;
  if (called++)
    abort ();
  yylval]]m4_if($1, 0,, [[[.tag]]])[[ = 'E';
  yylloc.first_line = yylloc.last_line = 1;
  yylloc.first_column = yylloc.last_column = 1;
  return 0;
}
]AT_YYERROR_DEFINE[

int
main (void)
{
  yydebug = 1;
  return yyparse ();
}
]])
AT_BISON_OPTION_POPDEFS

AT_BISON_CHECK([-o input$1.c input$1.y])
AT_COMPILE([input$1])
AT_PARSER_CHECK([./input$1], 0,
[[<]]kind[[> for 'E' @ 1.
<]]kind[[> for 'S' @ 1.
]],
[[Starting parse
Entering state 0
Reducing stack by rule 1 (line 46):
-> $$ = nterm start (1.1-1.1: <]]kind[[> for 'S' @ 1)
Stack now 0
Entering state 1
Reading a token: Now at end of input.
Shifting token END (1.1-1.1: <]]kind[[> for 'E' @ 1)
Entering state 2
Stack now 0 1 2
Cleanup: popping token END (1.1-1.1: <]]kind[[> for 'E' @ 1)
Cleanup: popping nterm start (1.1-1.1: <]]kind[[> for 'S' @ 1)
]])

m4_popdef([kind])
m4_popdef([not_kind])
])

_AT_CHECK_DEFAULT_PRINTER_AND_DESTRUCTOR_FOR_END_TOKEN(0)
_AT_CHECK_DEFAULT_PRINTER_AND_DESTRUCTOR_FOR_END_TOKEN(1)

AT_CLEANUP



## ------------------------------------------------------------------ ##
## Default %printer and %destructor are not for error or $undefined.  ##
## ------------------------------------------------------------------ ##

AT_SETUP([Default %printer and %destructor are not for error or $undefined])

# If Bison were to apply the default %printer and %destructor to the error
# token or to $undefined:
#   - For the error token:
#     - It would generate warnings for unused $n.
#     - It would invoke the %printer and %destructor on the error token's
#       semantic value, which would be initialized from the lookahead, which
#       would be destroyed separately.
#   - For $undefined, who knows what the semantic value would be.
AT_BISON_OPTION_PUSHDEFS
AT_DATA_GRAMMAR([[input.y]],
[[%debug

%{
# include <stdio.h>
# include <stdlib.h>
]AT_YYERROR_DECLARE[
]AT_YYLEX_DECLARE[
# define USE(SYM)
%}

%printer {
  fprintf (yyoutput, "'%c'", $$);
} <> <*>
%destructor {
  fprintf (stderr, "DESTROY '%c'\n", $$);
} <> <*>

%%

start:
  { $$ = 'S'; }
  /* In order to reveal the problems that this bug caused during parsing, add
   * $2 to USE.  */
  | 'a' error 'b' 'c' { USE(($1, $3, $4)); $$ = 'S'; }
  ;

%%
]AT_YYERROR_DEFINE[
]AT_YYLEX_DEFINE(["abd"], [yylval = res])[
int
main (void)
{
  yydebug = 1;
  return yyparse ();
}
]])
AT_BISON_OPTION_POPDEFS

AT_BISON_CHECK([-o input.c input.y])
AT_COMPILE([input])
AT_PARSER_CHECK([./input], [1], [],
[[Starting parse
Entering state 0
Reading a token: Next token is token 'a' ('a')
Shifting token 'a' ('a')
Entering state 1
Reading a token: Next token is token 'b' ('b')
syntax error
Shifting token error ()
Entering state 3
Next token is token 'b' ('b')
Shifting token 'b' ('b')
Entering state 5
Reading a token: Next token is token $undefined ()
Error: popping token 'b' ('b')
DESTROY 'b'
Stack now 0 1 3
Error: popping token error ()
Stack now 0 1
Shifting token error ()
Entering state 3
Next token is token $undefined ()
Error: discarding token $undefined ()
Error: popping token error ()
Stack now 0 1
Shifting token error ()
Entering state 3
Reading a token: Now at end of input.
Cleanup: discarding lookahead token $end ()
Stack now 0 1 3
Cleanup: popping token error ()
Cleanup: popping token 'a' ('a')
DESTROY 'a'
]])

AT_CLEANUP



## ------------------------------------------------------ ##
## Default %printer and %destructor are not for $accept.  ##
## ------------------------------------------------------ ##

AT_SETUP([Default %printer and %destructor are not for $accept])

# If YYSTYPE is a union and Bison were to apply the default %printer and
# %destructor to $accept:
#   - The %printer and %destructor code generated for $accept would always be
#     dead code because $accept is currently never shifted onto the stack.
#   - $$ for $accept would always be of type YYSTYPE because it's not possible
#     to declare `%type <field> $accept'.  (Also true for $undefined.)
#   - Thus, the compiler might complain that the user code assumes the wrong
#     type for $$ since the code might assume the type associated with a
#     specific union field, which is especially reasonable in C++ since that
#     type may be a base type.  This test case checks for this problem.  (Also
#     true for $undefined and the error token, so there are three warnings for
#     %printer and three for %destructor.)

AT_BISON_OPTION_PUSHDEFS
AT_DATA_GRAMMAR([[input.y]],
[[%debug /* So that %printer is actually compiled.  */

%{
# include <stdio.h>
# include <stdlib.h>
]AT_YYERROR_DECLARE[
]AT_YYLEX_DECLARE[
# define USE(SYM)
%}

%printer {
  char chr = $$;
  fprintf (yyoutput, "'%c'", chr);
} <> <*>
%destructor {
  char chr = $$;
  fprintf (stderr, "DESTROY '%c'\n", chr);
} <> <*>

%union { char chr; }
%type <chr> start

%%

start: { USE($$); } ;

%%
]AT_YYERROR_DEFINE[
]AT_YYLEX_DEFINE[
int
main (void)
{
  return yyparse ();
}
]])
AT_BISON_OPTION_POPDEFS

AT_BISON_CHECK([-o input.c input.y])
AT_COMPILE([input])

AT_CLEANUP



## ------------------------------------------------------ ##
## Default %printer and %destructor for mid-rule values.  ##
## ------------------------------------------------------ ##

AT_SETUP([Default %printer and %destructor for mid-rule values])

AT_BISON_OPTION_PUSHDEFS
AT_DATA_GRAMMAR([[input.y]],
[[%debug /* So that %printer is actually compiled.  */

%{
# include <stdio.h>
# include <stdlib.h>
]AT_YYERROR_DECLARE[
]AT_YYLEX_DECLARE[
# define USE(SYM)
# define YYLTYPE int
# define YYLLOC_DEFAULT(Current, Rhs, N) (void)(Rhs)
# define YY_LOCATION_PRINT(File, Loc)
%}

%printer { fprintf (yyoutput, "%d", @$); } <>
%destructor { fprintf (stderr, "DESTROY %d\n", @$); } <>
%printer { fprintf (yyoutput, "<*> printer should not be called"); } <*>
%destructor { fprintf (yyoutput, "<*> destructor should not be called"); } <*>

%%

start:
  {           @$ = 1; } // Not set or used.
  { USE ($$); @$ = 2; } // Both set and used.
  { USE ($$); @$ = 3; } // Only set.
  {           @$ = 4; } // Only used.
  'c'
  { USE (($$, $2, $4, $5)); @$ = 0; }
  ;

%%
]AT_YYERROR_DEFINE[
]AT_YYLEX_DEFINE[
int
main (void)
{
  yydebug = 1;
  return yyparse ();
}
]])
AT_BISON_OPTION_POPDEFS

AT_BISON_CHECK([-o input.c input.y], 0,,
[[input.y:33.3-23: warning: unset value: $$
input.y:30.3-35.37: warning: unused value: $3
]])

AT_COMPILE([input])
AT_PARSER_CHECK([./input], 1,,
[[Starting parse
Entering state 0
Reducing stack by rule 1 (line 30):
-> $$ = nterm $@1 (: )
Stack now 0
Entering state 2
Reducing stack by rule 2 (line 31):
-> $$ = nterm @2 (: 2)
Stack now 0 2
Entering state 4
Reducing stack by rule 3 (line 32):
-> $$ = nterm @3 (: 3)
Stack now 0 2 4
Entering state 5
Reducing stack by rule 4 (line 33):
-> $$ = nterm @4 (: 4)
Stack now 0 2 4 5
Entering state 6
Reading a token: Now at end of input.
syntax error
Error: popping nterm @4 (: 4)
DESTROY 4
Stack now 0 2 4 5
Error: popping nterm @3 (: 3)
DESTROY 3
Stack now 0 2 4
Error: popping nterm @2 (: 2)
DESTROY 2
Stack now 0 2
Error: popping nterm $@1 (: )
Stack now 0
Cleanup: discarding lookahead token $end (: )
Stack now 0
]])

AT_CLEANUP


## ----------------------- ##
## @$ implies %locations.  ##
## ----------------------- ##

# Bison once forgot to check for @$ in actions other than semantic actions.

# AT_CHECK_ACTION_LOCATIONS(ACTION-DIRECTIVE)
# -------------------------------------------
m4_define([AT_CHECK_ACTION_LOCATIONS],
[AT_SETUP([[@$ in ]$1[ implies %locations]])
AT_BISON_OPTION_PUSHDEFS
AT_DATA_GRAMMAR([[input.y]],
[[%code {
  #include <stdio.h>
]AT_YYERROR_DECLARE[
]AT_YYLEX_DECLARE[
}

%debug

]$1[ {
  fprintf (stderr, "%d\n", @$.first_line);
} ]m4_if($1, [%initial-action], [], [[start]])[

%%

start:  ;

%%

static int
yylex (void)
{
  return 0;
}

]AT_YYERROR_DEFINE[
int
main (void)
{
  return yyparse ();
}
]])

AT_BISON_CHECK([[-o input.c input.y]])
AT_COMPILE([[input]])
AT_BISON_OPTION_POPDEFS
AT_CLEANUP])

AT_CHECK_ACTION_LOCATIONS([[%initial-action]])
AT_CHECK_ACTION_LOCATIONS([[%destructor]])
AT_CHECK_ACTION_LOCATIONS([[%printer]])


## ------------------------- ##
## Qualified $$ in actions.  ##
## ------------------------- ##

# Check that we can used qualified $$ (v.g., $<type>$) not only in
# rule actions, but also where $$ is valid: %printer and %destructor.
#
# FIXME: Not actually checking %desctructor, but it's the same code as
# %printer...
#
# To do that, use a semantic value that has two fields (sem_type),
# declare symbols to have only one of these types (INT, float), and
# use $<type>$ to get the other one.  Including for symbols that are
# not typed (UNTYPED).

m4_pushdef([AT_TEST],
[AT_SETUP([[Qualified $$ in actions: $1]])

AT_BISON_OPTION_PUSHDEFS([%locations %skeleton "$1"])

AT_DATA_GRAMMAR([[input.y]],
[[%skeleton "$1"
%defines   // FIXME: Mandated by lalr1.cc in Bison 2.6.
%locations // FIXME: Mandated by lalr1.cc in Bison 2.6.
%debug
%code requires
{
  typedef struct sem_type
  {
    int ival;
    float fval;
  } sem_type;

# define YYSTYPE sem_type

]AT_SKEL_CC_IF([[
# include <iostream>
  static void
  report (std::ostream& yyo, int ival, float fval)
  {
    yyo << "ival: " << ival << ", fval: " <<  fval;
  }
]], [[
# include <stdio.h>
  static void
  report (FILE* yyo, int ival, float fval)
  {
    fprintf (yyo, "ival: %d, fval: %1.1f", ival, fval);
  }
]])[
}

%code
{
  ]AT_YYERROR_DECLARE[
  ]AT_YYLEX_DECLARE[
}

%token UNTYPED
%token <ival> INT
%type <fval> float
%printer { report (yyo, $$,       $<fval>$); } <ival>;
%printer { report (yyo, $<ival>$, $$      ); } <fval>;
%printer { report (yyo, $<ival>$, $<fval>$); } <>;

]AT_SKEL_CC_IF([[
/* The lalr1.cc skeleton, for backward compatibility, defines
   a constructor for position that initializes the filename.  The
   glr.cc skeleton does not (and in fact cannot: location/position
   are stored in a union, from which objects with constructors are
   excluded in C++). */
%initial-action {
  @$.initialize ();
}
]])[

%initial-action
{
  $<ival>$ = 42;
  $<fval>$ = 4.2;
}

%%
float: UNTYPED INT
{
  $$       = $<fval>1 + $<fval>2;
  $<ival>$ = $<ival>1 + $][2;
};
%%
]AT_YYERROR_DEFINE[
]AT_YYLEX_DEFINE(AT_SKEL_CC_IF([[{yy::parser::token::UNTYPED,
                                 yy::parser::token::INT,
                                  EOF}]],
                               [[{UNTYPED, INT, EOF}]]),
                 [AT_VAL.ival = toknum * 10; AT_VAL.fval = toknum / 10.0;])[
int
main (void)
{]AT_SKEL_CC_IF([[
  yy::parser p;
  p.set_debug_level(1);
  return p.parse ();]], [[
  yydebug = 1;
  return yyparse ();]])[
}
]])

AT_FULL_COMPILE([[input]])
AT_PARSER_CHECK([./input], 0, [], [stderr])
# Don't be too picky on the traces, GLR is not exactly the same.  Keep
# only the lines from the printer.
#
# Don't care about locations.  FIXME: remove their removal when Bison
# supports C++ without locations.
AT_CHECK([[sed -ne 's/([-0-9.]*: /(/;/ival:/p' stderr]], 0,
[[Reading a token: Next token is token UNTYPED (ival: 10, fval: 0.1)
Shifting token UNTYPED (ival: 10, fval: 0.1)
Reading a token: Next token is token INT (ival: 20, fval: 0.2)
Shifting token INT (ival: 20, fval: 0.2)
   $][1 = token UNTYPED (ival: 10, fval: 0.1)
   $][2 = token INT (ival: 20, fval: 0.2)
-> $$ = nterm float (ival: 30, fval: 0.3)
Cleanup: popping nterm float (ival: 30, fval: 0.3)
]])

AT_BISON_OPTION_POPDEFS

AT_CLEANUP
])

AT_TEST([yacc.c])
AT_TEST([glr.c])
AT_TEST([lalr1.cc])
AT_TEST([glr.cc])

m4_popdef([AT_TEST])

## ----------------------------------------------- ##
## Fix user actions without a trailing semicolon.  ##
## ----------------------------------------------- ##

AT_SETUP([[Fix user actions without a trailing semicolon]])

# This feature is undocumented, but we accidentally broke it in 2.3a,
# and there was a complaint at:
# <http://lists.gnu.org/archive/html/bug-bison/2008-11/msg00001.html>.
AT_BISON_OPTION_PUSHDEFS
AT_DATA([input.y],
[[%%
start: test2 test1 test0 testc;

test2
: 'a' { semi;			/* TEST:N:2 */ }
| 'b' { if (0) {no_semi}	/* TEST:N:2 */ }
| 'c' { if (0) {semi;}		/* TEST:N:2 */ }
| 'd' { semi;   no_semi		/* TEST:Y:2 */ }
| 'e' { semi(); no_semi()	/* TEST:Y:2 */ }
| 'f' { semi[]; no_semi[]	/* TEST:Y:2 */ }
| 'g' { semi++; no_semi++	/* TEST:Y:2 */ }
| 'h' { {no_semi} no_semi	/* TEST:Y:2 */ }
| 'i' { {semi;}   no_semi	/* TEST:Y:2 */ }
;
test1
  : 'a' { semi;			// TEST:N:1 ;
} | 'b' { if (0) {no_semi}	// TEST:N:1 ;
} | 'c' { if (0) {semi;}	// TEST:N:1 ;
} | 'd' { semi;   no_semi	// TEST:Y:1 ;
} | 'e' { semi(); no_semi()	// TEST:Y:1 ;
} | 'f' { semi[]; no_semi[]	// TEST:Y:1 ;
} | 'g' { semi++; no_semi++	// TEST:Y:1 ;
} | 'h' { {no_semi} no_semi	// TEST:Y:1 ;
} | 'i' { {semi;}   no_semi	// TEST:Y:1 ;
} ;
test0
  : 'a' { semi;			// TEST:N:1 {}
} | 'b' { if (0) {no_semi}	// TEST:N:1 {}
} | 'c' { if (0) {semi;}	// TEST:N:1 {}
} | 'd' { semi;   no_semi	// TEST:Y:1 {}
} | 'e' { semi(); no_semi()	// TEST:Y:1 {}
} | 'f' { semi[]; no_semi[]	// TEST:Y:1 {}
} | 'g' { semi++; no_semi++	// TEST:Y:1 {}
} | 'h' { {no_semi} no_semi	// TEST:Y:1 {}
} | 'i' { {semi;}   no_semi	// TEST:Y:1 {}
} ;

testc
: 'a' {
#define TEST_MACRO_N \
[]"broken\" $ @ $$ @$ [];\
string;"}
| 'b' {
no_semi
#define TEST_MACRO_N \
[]"broken\" $ @ $$ @$ [];\
string;"}
]])
AT_BISON_OPTION_POPDEFS

AT_BISON_CHECK([[-o input.c input.y]], [0], [],
[[input.y:8.48: warning: a ';' might be needed at the end of action code
input.y:8.48: warning: future versions of Bison will not add the ';'
input.y:9.48: warning: a ';' might be needed at the end of action code
input.y:9.48: warning: future versions of Bison will not add the ';'
input.y:10.48: warning: a ';' might be needed at the end of action code
input.y:10.48: warning: future versions of Bison will not add the ';'
input.y:11.48: warning: a ';' might be needed at the end of action code
input.y:11.48: warning: future versions of Bison will not add the ';'
input.y:12.48: warning: a ';' might be needed at the end of action code
input.y:12.48: warning: future versions of Bison will not add the ';'
input.y:13.48: warning: a ';' might be needed at the end of action code
input.y:13.48: warning: future versions of Bison will not add the ';'
input.y:20.1: warning: a ';' might be needed at the end of action code
input.y:20.1: warning: future versions of Bison will not add the ';'
input.y:21.1: warning: a ';' might be needed at the end of action code
input.y:21.1: warning: future versions of Bison will not add the ';'
input.y:22.1: warning: a ';' might be needed at the end of action code
input.y:22.1: warning: future versions of Bison will not add the ';'
input.y:23.1: warning: a ';' might be needed at the end of action code
input.y:23.1: warning: future versions of Bison will not add the ';'
input.y:24.1: warning: a ';' might be needed at the end of action code
input.y:24.1: warning: future versions of Bison will not add the ';'
input.y:25.1: warning: a ';' might be needed at the end of action code
input.y:25.1: warning: future versions of Bison will not add the ';'
input.y:31.1: warning: a ';' might be needed at the end of action code
input.y:31.1: warning: future versions of Bison will not add the ';'
input.y:32.1: warning: a ';' might be needed at the end of action code
input.y:32.1: warning: future versions of Bison will not add the ';'
input.y:33.1: warning: a ';' might be needed at the end of action code
input.y:33.1: warning: future versions of Bison will not add the ';'
input.y:34.1: warning: a ';' might be needed at the end of action code
input.y:34.1: warning: future versions of Bison will not add the ';'
input.y:35.1: warning: a ';' might be needed at the end of action code
input.y:35.1: warning: future versions of Bison will not add the ';'
input.y:36.1: warning: a ';' might be needed at the end of action code
input.y:36.1: warning: future versions of Bison will not add the ';'
]])

AT_MATCHES_CHECK([input.c], [[/\* TEST:N:2 \*/ \}$]],       [[3]])
AT_MATCHES_CHECK([input.c], [[/\* TEST:Y:2 \*/ ;\}$]],      [[6]])
AT_MATCHES_CHECK([input.c], [[// TEST:N:1 [;{}]*\n\}$]],    [[6]])
AT_MATCHES_CHECK([input.c], [[// TEST:Y:1 [;{}]*\n;\}$]],  [[12]])
AT_MATCHES_CHECK([input.c], [[#define TEST_MACRO_N \\\n\[\]"broken\\" \$ \@ \$\$ \@\$ \[\];\\\nstring;"\}]], [[2]])

AT_CLEANUP


## -------------------------------------------------- ##
## Destroying lookahead assigned by semantic action.  ##
## -------------------------------------------------- ##

AT_SETUP([[Destroying lookahead assigned by semantic action]])

AT_BISON_OPTION_PUSHDEFS
AT_DATA_GRAMMAR([input.y],
[[
%code {
  #include <assert.h>
  #include <stdio.h>
]AT_YYERROR_DECLARE[
]AT_YYLEX_DECLARE[
  #define USE(Var)
}

%destructor { fprintf (stderr, "'a' destructor\n"); } 'a'
%destructor { fprintf (stderr, "'b' destructor\n"); } 'b'

%%

// In a previous version of Bison, yychar assigned by the semantic
// action below was not translated into yytoken before the lookahead was
// discarded and thus before its destructor (selected according to
// yytoken) was called in order to return from yyparse.  This would
// happen even if YYACCEPT was performed in a later semantic action as
// long as only consistent states with default reductions were visited
// in between.  However, we leave YYACCEPT in the same semantic action
// for this test in order to show that skeletons cannot simply translate
// immediately after every semantic action because a semantic action
// that has set yychar might not always return normally.  Instead,
// skeletons must translate before every use of yytoken.
start: 'a' accept { USE($1); } ;
accept: /*empty*/ {
  assert (yychar == YYEMPTY);
  yychar = 'b';
  YYACCEPT;
} ;

%%
]AT_YYERROR_DEFINE[
]AT_YYLEX_DEFINE(["a"])[
int
main (void)
{
  return yyparse ();
}
]])
AT_BISON_OPTION_POPDEFS
AT_BISON_CHECK([[-o input.c input.y]])
AT_COMPILE([[input]])
AT_PARSER_CHECK([[./input]], [[0]], [],
[['b' destructor
'a' destructor
]])

AT_CLEANUP

## ---------- ##
## YYBACKUP.  ##
## ---------- ##

AT_SETUP([[YYBACKUP]])

AT_BISON_OPTION_PUSHDEFS([%pure-parser])

AT_DATA_GRAMMAR([input.y],
[[
%error-verbose
%debug
%pure-parser
%code {
# include <stdio.h>
# include <stdlib.h>
# include <assert.h>

  ]AT_YYERROR_DECLARE[
  ]AT_YYLEX_DECLARE[
}
%%
input:
  exp exp {}
;

exp:
  'a'     { printf ("a: %d\n", $1); }
| 'b'     { YYBACKUP('a', 123); }
| 'c' 'd' { YYBACKUP('a', 456); }
;

%%
]AT_YYERROR_DEFINE[
]AT_YYLEX_DEFINE(["bcd"], [*lvalp = (toknum + 1) * 10])[

int
main (void)
{
  yydebug = !!getenv("YYDEBUG");
  return yyparse ();
}
]])
AT_BISON_OPTION_POPDEFS

AT_BISON_CHECK([[-o input.c input.y]])
AT_COMPILE([[input]])
AT_PARSER_CHECK([[./input]], [[0]],
[[a: 123
a: 456
]])

AT_CLEANUP