# Exercising Bison on counterexamples.                         -*- Autotest -*-

# Copyright (C) 2020-2022 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 <https://www.gnu.org/licenses/>.

AT_BANNER([[Counterexamples.]])

# AT_BISON_CHECK_CEX(TREE, FLAT)
# ------------------------------
m4_define([AT_BISON_CHECK_CEX],
[AT_KEYWORDS([cex])

AT_BISON_CHECK([-Wcounterexamples input.y], [0], [], [stderr])
# FIXME: Avoid trailing white spaces.
AT_CHECK([[sed -e 's/time limit exceeded: [0-9][.0-9]*/time limit exceeded: XXX/g;s/ *$//;' stderr]],
         [], [$1])

m4_pushdef([AT_SET_ENV_IF],
           [[YYFLAT=1; export YYFLAT;]]m4_defn([AT_SET_ENV_IF]))
AT_BISON_CHECK([-Wcounterexamples input.y], [0], [], [stderr])
AT_CHECK([[sed -e 's/time limit exceeded: [0-9][.0-9]*/time limit exceeded: XXX/g' stderr]],
         [], [$2])
m4_popdef([AT_SET_ENV_IF])

])

## --------------------- ##
## Simple Unifying S/R.  ##
## --------------------- ##

AT_SETUP([Unifying S/R])

AT_DATA([[input.y]],
[[%token A B C
%%
s: a x | y c;
a: A;
c: C;
x: B | B C;
y: A | A B;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example: A . B C
  Shift derivation
    s
    `-> 2: y            c
           `-> 8: A . B `-> 4: C
  Reduce derivation
    s
    `-> 1: a          x
           `-> 3: A . `-> 6: B C
input.y:4.4: warning: rule useless in parser due to conflicts [-Wother]
]],
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example           A . B C
  Shift derivation  s -> [ y -> [ A . B ] c -> [ C ] ]
  Reduce derivation s -> [ a -> [ A . ] x -> [ B C ] ]
input.y:4.4: warning: rule useless in parser due to conflicts [-Wother]
]])

AT_CLEANUP

## ------------------- ##
## Deep Unifying S/R.  ##
## ------------------- ##

AT_SETUP([Deep Unifying S/R])

AT_DATA([[input.y]],
[[%token A B C
%%
s: ac | a bc;
ac: A ac C | b;
b: B | B b;
a: A | A a;
bc: B bc C | B C;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example: A . B C
  Shift derivation
    s
    `-> 1: ac
           `-> 3: A ac                C
                    `-> 4: b
                           `-> 5: . B
  Reduce derivation
    s
    `-> 2: a          bc
           `-> 7: A . `-> 10: B C
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example: A A . B B C C
  Shift derivation
    s
    `-> 1: ac
           `-> 3: A ac                                    C
                    `-> 3: A ac                         C
                             `-> 4: b
                                    `-> 6: . b
                                             `-> 5: B B
  Reduce derivation
    s
    `-> 2: a                   bc
           `-> 8: A a          `-> 9: B bc          C
                    `-> 7: A .          `-> 10: B C
input.y:6.4: warning: rule useless in parser due to conflicts [-Wother]
]],
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example           A . B C
  Shift derivation  s -> [ ac -> [ A ac -> [ b -> [ . B ] ] C ] ]
  Reduce derivation s -> [ a -> [ A . ] bc -> [ B C ] ]
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example           A A . B B C C
  Shift derivation  s -> [ ac -> [ A ac -> [ A ac -> [ b -> [ . b -> [ B B ] ] ] C ] C ] ]
  Reduce derivation s -> [ a -> [ A a -> [ A . ] ] bc -> [ B bc -> [ B C ] C ] ]
input.y:6.4: warning: rule useless in parser due to conflicts [-Wother]
]])

AT_CLEANUP

## ------------------------------------ ##
## S/R Conflict with Nullable Symbols.  ##
## ------------------------------------ ##

AT_SETUP([S/R Conflict with Nullable Symbols])

AT_DATA([[input.y]],
[[%token A B X Y
%%
s: ax by | A xby;
ax: A x;
x: %empty | X x;
by: B y;
y: %empty | Y y;
xby: B | X xby Y;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 2 shift/reduce conflicts [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example: A . B
  Shift derivation
    s
    `-> 2: A xby
             `-> 9: . B
  Reduce derivation
    s
    `-> 1: ax                       by
           `-> 3: A x               `-> 6: B y
                    `-> 4: %empty .          `-> 6: %empty
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  First example: A X . B Y $end
  Shift derivation
    $accept
    `-> 0: s                               $end
           `-> 2: A xby
                    `-> 10: X xby        Y
                              `-> 9: . B
  Second example: A X . B y $end
  Reduce derivation
    $accept
    `-> 0: s                                                   $end
           `-> 1: ax                                by
                  `-> 3: A x                        `-> 6: B y
                           `-> 5: X x
                                    `-> 4: %empty .
input.y:5.4-9: warning: rule useless in parser due to conflicts [-Wother]
]],
[[input.y: warning: 2 shift/reduce conflicts [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example           A . B
  Shift derivation  s -> [ A xby -> [ . B ] ]
  Reduce derivation s -> [ ax -> [ A x -> [ . ] ] by -> [ B y -> [ ] ] ]
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  First example     A X . B Y $end
  Shift derivation  $accept -> [ s -> [ A xby -> [ X xby -> [ . B ] Y ] ] $end ]
  Second example    A X . B y $end
  Reduce derivation $accept -> [ s -> [ ax -> [ A x -> [ X x -> [ . ] ] ] by -> [ B y ] ] $end ]
input.y:5.4-9: warning: rule useless in parser due to conflicts [-Wother]
]])

AT_CLEANUP

## ---------------------------- ##
## Non-unifying Ambiguous S/R.  ##
## ---------------------------- ##

AT_SETUP([Non-unifying Ambiguous S/R])

AT_DATA([[input.y]],
[[%token A B C D E
%%
g: s | x;
s: A x E | A x D E;
x: b cd | bc;
b: B;
cd: C D;
bc: B C;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token C [-Wcounterexamples]
  First example: B . C $end
  Shift derivation
    $accept
    `-> 0: g                          $end
           `-> 2: x
                  `-> 6: bc
                         `-> 9: B . C
  Second example: B . C D $end
  Reduce derivation
    $accept
    `-> 0: g                                   $end
           `-> 2: x
                  `-> 5: b          cd
                         `-> 7: B . `-> 8: C D
input.y:6.4: warning: rule useless in parser due to conflicts [-Wother]
]],
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token C [-Wcounterexamples]
  First example     B . C $end
  Shift derivation  $accept -> [ g -> [ x -> [ bc -> [ B . C ] ] ] $end ]
  Second example    B . C D $end
  Reduce derivation $accept -> [ g -> [ x -> [ b -> [ B . ] cd -> [ C D ] ] ] $end ]
input.y:6.4: warning: rule useless in parser due to conflicts [-Wother]
]])

AT_CLEANUP

## ------------------------------ ##
## Non-unifying Unambiguous S/R.  ##
## ------------------------------ ##

AT_SETUP([Non-unifying Unambiguous S/R])

AT_DATA([[input.y]],
[[%token A B
%%
s: t | s t;
t: x | y;
x: A;
y: A A B;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token A [-Wcounterexamples]
  First example: A . A B $end
  Shift derivation
    $accept
    `-> 0: s                            $end
           `-> 1: t
                  `-> 4: y
                         `-> 6: A . A B
  Second example: A . A $end
  Reduce derivation
    $accept
    `-> 0: s                                               $end
           `-> 2: s                        t
                  `-> 1: t                 `-> 3: x
                         `-> 3: x                 `-> 5: A
                                `-> 5: A .
]],
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token A [-Wcounterexamples]
  First example     A . A B $end
  Shift derivation  $accept -> [ s -> [ t -> [ y -> [ A . A B ] ] ] $end ]
  Second example    A . A $end
  Reduce derivation $accept -> [ s -> [ s -> [ t -> [ x -> [ A . ] ] ] t -> [ x -> [ A ] ] ] $end ]
]])

AT_CLEANUP

## ----------------------- ##
## S/R after first token.  ##
## ----------------------- ##

AT_SETUP([S/R after first token])

AT_DATA([[input.y]],
[[%token A B X Y
%%
a: r t | s;
r: b;
b: B;
t: A xx | A x xy;
s: b A xx y;
x: X;
xx: X X;
xy: X Y;
y: Y;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 2 shift/reduce conflicts [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token A [-Wcounterexamples]
  Example: b . A X X Y
  Shift derivation
    a
    `-> 2: s
           `-> 7: b . xx           y
                      `-> 9: A X X `-> 11: Y
  Reduce derivation
    a
    `-> 1: r          t
           `-> 3: b . `-> 6: A x        xy
                               `-> 8: X `-> 10: X Y
input.y: warning: shift/reduce conflict on token X [-Wcounterexamples]
  First example: A X . X
  Shift derivation
    a
    `-> 1: t
           `-> 5: A xx
                    `-> 9: X . X
  Second example: X . X xy
  Reduce derivation
    a
    `-> 1: x          t
           `-> 8: X . `-> 6: X xy
input.y:4.4: warning: rule useless in parser due to conflicts [-Wother]
input.y:8.4: warning: rule useless in parser due to conflicts [-Wother]
]],
[[input.y: warning: 2 shift/reduce conflicts [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token A [-Wcounterexamples]
  Example           b . A X X Y
  Shift derivation  a -> [ s -> [ b . xx -> [ A X X ] y -> [ Y ] ] ]
  Reduce derivation a -> [ r -> [ b . ] t -> [ A x -> [ X ] xy -> [ X Y ] ] ]
input.y: warning: shift/reduce conflict on token X [-Wcounterexamples]
  First example     A X . X
  Shift derivation  a -> [ t -> [ A xx -> [ X . X ] ] ]
  Second example    X . X xy
  Reduce derivation a -> [ x -> [ X . ] t -> [ X xy ] ]
input.y:4.4: warning: rule useless in parser due to conflicts [-Wother]
input.y:8.4: warning: rule useless in parser due to conflicts [-Wother]
]])

AT_CLEANUP

## ----------------------------- ##
## Unifying R/R counterexample.  ##
## ----------------------------- ##

AT_SETUP([Unifying R/R counterexample])

AT_DATA([[input.y]],
[[%token A
%%
a : A b ;
b : A | b;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
input.y: warning: reduce/reduce conflict on token $end [-Wcounterexamples]
  Example: A b .
  First reduce derivation
    a
    `-> 1: A b .
  Second reduce derivation
    a
    `-> 1: A b
             `-> 3: b .
input.y:4.9: warning: rule useless in parser due to conflicts [-Wother]
]],
[[input.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
input.y: warning: reduce/reduce conflict on token $end [-Wcounterexamples]
  Example                  A b .
  First reduce derivation  a -> [ A b . ]
  Second reduce derivation a -> [ A b -> [ b . ] ]
input.y:4.9: warning: rule useless in parser due to conflicts [-Wother]
]])

AT_CLEANUP

## --------------------------------- ##
## Non-unifying R/R LR(1) conflict.  ##
## --------------------------------- ##

AT_SETUP([Non-unifying R/R LR(1) conflict])

AT_DATA([[input.y]],
[[%token A B C D
%%
s: a A | B a C | b C | B b A;
a: D;
b: D;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 2 reduce/reduce conflicts [-Wconflicts-rr]
input.y: warning: reduce/reduce conflict on tokens A, C [-Wcounterexamples]
  First example: D . A $end
  First reduce derivation
    $accept
    `-> 0: s                   $end
           `-> 1: a          A
                  `-> 5: D .
  Second example: B D . A $end
  Second reduce derivation
    $accept
    `-> 0: s                     $end
           `-> 4: B b          A
                    `-> 6: D .
input.y:5.4: warning: rule useless in parser due to conflicts [-Wother]
]],
[[input.y: warning: 2 reduce/reduce conflicts [-Wconflicts-rr]
input.y: warning: reduce/reduce conflict on tokens A, C [-Wcounterexamples]
  First example            D . A $end
  First reduce derivation  $accept -> [ s -> [ a -> [ D . ] A ] $end ]
  Second example           B D . A $end
  Second reduce derivation $accept -> [ s -> [ B b -> [ D . ] A ] $end ]
input.y:5.4: warning: rule useless in parser due to conflicts [-Wother]
]])

AT_CLEANUP

## --------------------------------- ##
## Non-unifying R/R LR(2) conflict.  ##
## --------------------------------- ##

AT_SETUP([Non-unifying R/R LR(2) conflict])

AT_DATA([[input.y]],
[[%token H J K X
%%
s: a J;
a: H i;
i: X | i J K;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token J [-Wcounterexamples]
time limit exceeded: XXX
  First example: H i . J K $end
  Shift derivation
    $accept
    `-> 0: a                       $end
           `-> 2: H i
                    `-> 4: i . J K
  Second example: H i . J $end
  Reduce derivation
    $accept
    `-> 0: s                     $end
           `-> 1: a            J
                  `-> 2: H i .
input.y:4.4-6: warning: rule useless in parser due to conflicts [-Wother]
]],
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token J [-Wcounterexamples]
time limit exceeded: XXX
  First example     H i . J K $end
  Shift derivation  $accept -> [ a -> [ H i -> [ i . J K ] ] $end ]
  Second example    H i . J $end
  Reduce derivation $accept -> [ s -> [ a -> [ H i . ] J ] $end ]
input.y:4.4-6: warning: rule useless in parser due to conflicts [-Wother]
]])

AT_CLEANUP

## -------------------- ##
## Cex Search Prepend.  ##
## -------------------- ##

# Tests prepend steps in uniying counterexample
# graph search

AT_SETUP([Cex Search Prepend])

AT_DATA([[input.y]],
[[%token N A B C D
%%
s: n | n C;
n: N n D | N n C | N a B | N b;
a: A;
b: A B C | A B D;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example: N A . B C
  Shift derivation
    s
    `-> 1: n
           `-> 6: N b
                    `-> 8: A . B C
  Reduce derivation
    s
    `-> 2: n                     C
           `-> 5: N a          B
                    `-> 7: A .
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example: N N A . B D C
  Shift derivation
    s
    `-> 1: n
           `-> 4: N n                       C
                    `-> 6: N b
                             `-> 9: A . B D
  Reduce derivation
    s
    `-> 2: n                                C
           `-> 3: N n                     D
                    `-> 5: N a          B
                             `-> 7: A .
input.y:5.4: warning: rule useless in parser due to conflicts [-Wother]
]],
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example           N A . B C
  Shift derivation  s -> [ n -> [ N b -> [ A . B C ] ] ]
  Reduce derivation s -> [ n -> [ N a -> [ A . ] B ] C ]
input.y: warning: shift/reduce conflict on token B [-Wcounterexamples]
  Example           N N A . B D C
  Shift derivation  s -> [ n -> [ N n -> [ N b -> [ A . B D ] ] C ] ]
  Reduce derivation s -> [ n -> [ N n -> [ N a -> [ A . ] B ] D ] C ]
input.y:5.4: warning: rule useless in parser due to conflicts [-Wother]
]])

AT_CLEANUP

## ------------------- ##
## R/R cex with prec.  ##
## ------------------- ##

# Tests that counterexamples containing rules using
# precedence/associativity directives work.

AT_SETUP([R/R cex with prec])

AT_DATA([[input.y]],
[[%left b
%right c
%%
S: B C | C B;
A : B  | C  | %empty;
B : A b A;
C : A c A;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 4 reduce/reduce conflicts [-Wconflicts-rr]
input.y: warning: reduce/reduce conflict on tokens b, c [-Wcounterexamples]
  Example: B . b c
  First reduce derivation
    S
    `-> 1: B                                 C
           `-> 6: A          b A             `-> 7: A             c A
                  `-> 3: B .   `-> 6: %empty        `-> 7: %empty   `-> 7: %empty
  Second reduce derivation
    S
    `-> 1: B C
             `-> 7: A                                             c A
                    `-> 3: B                                        `-> 7: %empty
                           `-> 6: A               b A
                                  `-> 5: %empty .   `-> 6: %empty
input.y: warning: reduce/reduce conflict on tokens b, c [-Wcounterexamples]
  Example: C . c b
  First reduce derivation
    S
    `-> 2: C                                 B
           `-> 7: A          c A             `-> 6: A             b A
                  `-> 4: C .   `-> 7: %empty        `-> 6: %empty   `-> 6: %empty
  Second reduce derivation
    S
    `-> 2: C B
             `-> 6: A                                             b A
                    `-> 4: C                                        `-> 6: %empty
                           `-> 7: A               c A
                                  `-> 5: %empty .   `-> 7: %empty
]],
[[input.y: warning: 4 reduce/reduce conflicts [-Wconflicts-rr]
input.y: warning: reduce/reduce conflict on tokens b, c [-Wcounterexamples]
  Example                  B . b c
  First reduce derivation  S -> [ B -> [ A -> [ B . ] b A -> [ ] ] C -> [ A -> [ ] c A -> [ ] ] ]
  Second reduce derivation S -> [ B C -> [ A -> [ B -> [ A -> [ . ] b A -> [ ] ] ] c A -> [ ] ] ]
input.y: warning: reduce/reduce conflict on tokens b, c [-Wcounterexamples]
  Example                  C . c b
  First reduce derivation  S -> [ C -> [ A -> [ C . ] c A -> [ ] ] B -> [ A -> [ ] b A -> [ ] ] ]
  Second reduce derivation S -> [ C B -> [ A -> [ C -> [ A -> [ . ] c A -> [ ] ] ] b A -> [ ] ] ]
]])

AT_CLEANUP

## ------------------- ##
## Null nonterminals.  ##
## ------------------- ##

AT_SETUP([Null nonterminals])

AT_DATA([[input.y]],
[[%token A
%%
a : b d | c d ;
b : ;
c : ;
d : a | c A | d;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: 6 reduce/reduce conflicts [-Wconflicts-rr]
input.y: warning: reduce/reduce conflict on token A [-Wcounterexamples]
  First example: . c A A $end
  First reduce derivation
    $accept
    `-> 0: a                                   $end
           `-> 1: b               d
                  `-> 3: %empty . `-> 6: c A A
  Second example: . c A A $end
  Second reduce derivation
    $accept
    `-> 0: a                                   $end
           `-> 2: c               d
                  `-> 4: %empty . `-> 6: c A A
input.y: warning: reduce/reduce conflict on token A [-Wcounterexamples]
time limit exceeded: XXX
  First example: b . c A A $end
  First reduce derivation
    $accept
    `-> 0: a                                                   $end
           `-> 1: b d
                    `-> 5: a
                           `-> 1: b               d
                                  `-> 3: %empty . `-> 6: c A A
  Second example: b . A $end
  Second reduce derivation
    $accept
    `-> 0: a                                 $end
           `-> 1: b d
                    `-> 6: c               A
                           `-> 4: %empty .
input.y: warning: reduce/reduce conflict on token A [-Wcounterexamples]
time limit exceeded: XXX
  First example: c . c A A $end
  First reduce derivation
    $accept
    `-> 0: a                                                   $end
           `-> 2: c d
                    `-> 5: a
                           `-> 1: b               d
                                  `-> 3: %empty . `-> 6: c A A
  Second example: c . A $end
  Second reduce derivation
    $accept
    `-> 0: a                                 $end
           `-> 2: c d
                    `-> 6: c               A
                           `-> 4: %empty .
input.y: warning: shift/reduce conflict on token A [-Wcounterexamples]
time limit exceeded: XXX
  First example: b c . A
  Shift derivation
    a
    `-> 1: b d
             `-> 6: c . A
  Second example: b c . c A A $end
  Reduce derivation
    $accept
    `-> 0: a                                                                   $end
           `-> 1: b d
                    `-> 5: a
                           `-> 2: c d
                                    `-> 5: a
                                           `-> 1: b               d
                                                  `-> 3: %empty . `-> 6: c A A
input.y: warning: reduce/reduce conflict on token A [-Wcounterexamples]
  First example: b c . c A A $end
  First reduce derivation
    $accept
    `-> 0: a                                                                   $end
           `-> 1: b d
                    `-> 5: a
                           `-> 2: c d
                                    `-> 5: a
                                           `-> 1: b               d
                                                  `-> 3: %empty . `-> 6: c A A
  Second example: b c . A $end
  Second reduce derivation
    $accept
    `-> 0: a                                                 $end
           `-> 1: b d
                    `-> 5: a
                           `-> 2: c d
                                    `-> 6: c               A
                                           `-> 4: %empty .
input.y: warning: shift/reduce conflict on token A [-Wcounterexamples]
  First example: b c . A
  Shift derivation
    a
    `-> 1: b d
             `-> 6: c . A
  Second example: b c . A $end
  Reduce derivation
    $accept
    `-> 0: a                                                 $end
           `-> 1: b d
                    `-> 5: a
                           `-> 2: c d
                                    `-> 6: c               A
                                           `-> 4: %empty .
input.y: warning: reduce/reduce conflict on token $end [-Wcounterexamples]
  Example: b d .
  First reduce derivation
    a
    `-> 1: b d .
  Second reduce derivation
    a
    `-> 1: b d
             `-> 7: d .
input.y: warning: reduce/reduce conflict on token $end [-Wcounterexamples]
  Example: c d .
  First reduce derivation
    a
    `-> 2: c d .
  Second reduce derivation
    a
    `-> 2: c d
             `-> 7: d .
input.y:5.4: warning: rule useless in parser due to conflicts [-Wother]
input.y:6.15: warning: rule useless in parser due to conflicts [-Wother]
]],
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: 6 reduce/reduce conflicts [-Wconflicts-rr]
input.y: warning: reduce/reduce conflict on token A [-Wcounterexamples]
  First example            . c A A $end
  First reduce derivation  $accept -> [ a -> [ b -> [ . ] d -> [ c A A ] ] $end ]
  Second example           . c A A $end
  Second reduce derivation $accept -> [ a -> [ c -> [ . ] d -> [ c A A ] ] $end ]
input.y: warning: reduce/reduce conflict on token A [-Wcounterexamples]
time limit exceeded: XXX
  First example            b . c A A $end
  First reduce derivation  $accept -> [ a -> [ b d -> [ a -> [ b -> [ . ] d -> [ c A A ] ] ] ] $end ]
  Second example           b . A $end
  Second reduce derivation $accept -> [ a -> [ b d -> [ c -> [ . ] A ] ] $end ]
input.y: warning: reduce/reduce conflict on token A [-Wcounterexamples]
time limit exceeded: XXX
  First example            c . c A A $end
  First reduce derivation  $accept -> [ a -> [ c d -> [ a -> [ b -> [ . ] d -> [ c A A ] ] ] ] $end ]
  Second example           c . A $end
  Second reduce derivation $accept -> [ a -> [ c d -> [ c -> [ . ] A ] ] $end ]
input.y: warning: shift/reduce conflict on token A [-Wcounterexamples]
time limit exceeded: XXX
  First example     b c . A
  Shift derivation  a -> [ b d -> [ c . A ] ]
  Second example    b c . c A A $end
  Reduce derivation $accept -> [ a -> [ b d -> [ a -> [ c d -> [ a -> [ b -> [ . ] d -> [ c A A ] ] ] ] ] ] $end ]
input.y: warning: reduce/reduce conflict on token A [-Wcounterexamples]
  First example            b c . c A A $end
  First reduce derivation  $accept -> [ a -> [ b d -> [ a -> [ c d -> [ a -> [ b -> [ . ] d -> [ c A A ] ] ] ] ] ] $end ]
  Second example           b c . A $end
  Second reduce derivation $accept -> [ a -> [ b d -> [ a -> [ c d -> [ c -> [ . ] A ] ] ] ] $end ]
input.y: warning: shift/reduce conflict on token A [-Wcounterexamples]
  First example     b c . A
  Shift derivation  a -> [ b d -> [ c . A ] ]
  Second example    b c . A $end
  Reduce derivation $accept -> [ a -> [ b d -> [ a -> [ c d -> [ c -> [ . ] A ] ] ] ] $end ]
input.y: warning: reduce/reduce conflict on token $end [-Wcounterexamples]
  Example                  b d .
  First reduce derivation  a -> [ b d . ]
  Second reduce derivation a -> [ b d -> [ d . ] ]
input.y: warning: reduce/reduce conflict on token $end [-Wcounterexamples]
  Example                  c d .
  First reduce derivation  a -> [ c d . ]
  Second reduce derivation a -> [ c d -> [ d . ] ]
input.y:5.4: warning: rule useless in parser due to conflicts [-Wother]
input.y:6.15: warning: rule useless in parser due to conflicts [-Wother]
]])

AT_CLEANUP

## --------------------------- ##
## Non-unifying Prefix Share.  ##
## --------------------------- ##

AT_SETUP([Non-unifying Prefix Share])

# Tests for a counterexample which should start its derivation
# at a shared symbol rather than the start symbol.

AT_DATA([[input.y]],
[[%token H J
%%
s: a | a J;
a: H i J J
i: %empty | i J;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token J [-Wcounterexamples]
  Example: H i J . J J
  Shift derivation
    s
    `-> 2: a                J
           `-> 3: H i J . J
  Reduce derivation
    s
    `-> 1: a
           `-> 3: H i            J J
                    `-> 5: i J .
input.y:5.13-15: warning: rule useless in parser due to conflicts [-Wother]
]],
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token J [-Wcounterexamples]
  Example           H i J . J J
  Shift derivation  s -> [ a -> [ H i J . J ] J ]
  Reduce derivation s -> [ a -> [ H i -> [ i J . ] J J ] ]
input.y:5.13-15: warning: rule useless in parser due to conflicts [-Wother]
]])

AT_CLEANUP

## -------------------- ##
## Deep Null Unifying.  ##
## ---------------------##

# Tests that nested nullable nonterminals
# are derived correctly.

AT_SETUP([Deep Null Unifying])

AT_DATA([[input.y]],
[[%token A D
%%
s: A a d | A a a d;
a: b;
b: c
c: %empty
d: D;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token D [-Wcounterexamples]
  Example: A a . D
  Shift derivation
    s
    `-> 1: A a d
               `-> 6: . D
  Reduce derivation
    s
    `-> 2: A a a                             d
               `-> 3: b                      `-> 6: D
                      `-> 4: c
                             `-> 5: %empty .
]],
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token D [-Wcounterexamples]
  Example           A a . D
  Shift derivation  s -> [ A a d -> [ . D ] ]
  Reduce derivation s -> [ A a a -> [ b -> [ c -> [ . ] ] ] d -> [ D ] ]
]])

AT_CLEANUP

## ------------------------ ##
## Deep Null Non-unifying.  ##
## -------------------------##

# Tests that expand_to_conflict works with nullable sybols

AT_SETUP([Deep Null Non-unifying])

AT_DATA([[input.y]],
[[%token A D E
%%
s: A a d | A a a d E;
a: b;
b: c
c: %empty
d: D;
]])

AT_BISON_CHECK_CEX(
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token D [-Wcounterexamples]
  First example: A a . D $end
  Shift derivation
    $accept
    `-> 0: s                     $end
           `-> 1: A a d
                      `-> 6: . D
  Second example: A a . D E $end
  Reduce derivation
    $accept
    `-> 0: s                                                   $end
           `-> 2: A a a                             d        E
                      `-> 3: b                      `-> 6: D
                             `-> 4: c
                                    `-> 5: %empty .
]],
[[input.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
input.y: warning: shift/reduce conflict on token D [-Wcounterexamples]
  First example     A a . D $end
  Shift derivation  $accept -> [ s -> [ A a d -> [ . D ] ] $end ]
  Second example    A a . D E $end
  Reduce derivation $accept -> [ s -> [ A a a -> [ b -> [ c -> [ . ] ] ] d -> [ D ] E ] $end ]
]])

AT_CLEANUP