Thank the developer of the initial push parser implementation.

[bison.git] / tests / conflicts.at

diff --git a/tests/conflicts.at b/tests/conflicts.at
index 21ba86d7529c63c81abe7bed806f9f1747a21ffe..705419b95b8c296c685a6664540f3463470f1335 100644 (file)
--- a/tests/conflicts.at
+++ b/tests/conflicts.at
@@ -1,21 +1,19 @@
 # Exercising Bison on conflicts.                         -*- Autotest -*-
 
 # Exercising Bison on conflicts.                         -*- Autotest -*-
 

-# Copyright (C) 2002, 2003, 2004, 2005, 2007 Free Software Foundation, Inc.
+# Copyright (C) 2002-2005, 2007-2010 Free Software Foundation, Inc.

 
 

-# This program is free software; you can redistribute it and/or modify
+# 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
 # it under the terms of the GNU General Public License as published by

-# the Free Software Foundation; either version 2, or (at your option)
-# any later version.
-
+# 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.
 # 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
 # You should have received a copy of the GNU General Public License

-# along with this program; if not, write to the Free Software
-# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
-# 02110-1301, USA.
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.

 
 AT_BANNER([[Conflicts.]])
 
 
 AT_BANNER([[Conflicts.]])
 


@@ -38,8 +36,8 @@ exp: e 'e';
 e: 'e' | /* Nothing. */;
 ]])
 
 e: 'e' | /* Nothing. */;
 ]])
 

-AT_CHECK([bison -o input.c input.y], 0, [],
-[[input.y:4.9: warning: rule never reduced because of conflicts: e: /* empty */
+AT_BISON_CHECK([-o input.c input.y], 0, [],
+[[input.y:4.9: warning: rule useless in parser due to conflicts: e: /* empty */

 ]])
 
 AT_CLEANUP
 ]])
 
 AT_CLEANUP


@@ -90,32 +88,176 @@ expr: expr '<' expr
 int
 main (int argc, const char *argv[])
 {
 int
 main (int argc, const char *argv[])
 {

-  input = argc <= 1 ? "" : argv[1];    
+  input = argc <= 1 ? "" : argv[1];

   return yyparse ();
 }
 ]])
 
 # Specify the output files to avoid problems on different file systems.
   return yyparse ();
 }
 ]])
 
 # Specify the output files to avoid problems on different file systems.

-AT_CHECK([bison -o input.c input.y])
+AT_BISON_CHECK([-o input.c input.y])

 AT_COMPILE([input])
 
 AT_PARSER_CHECK([./input '0<0'])
 AT_COMPILE([input])
 
 AT_PARSER_CHECK([./input '0<0'])

-# FIXME: This is an actual bug, but a new one, in the sense that
-# no one has ever spotted it!  The messages are *wrong*: there should
-# be nothing there, it should be expected eof.

 AT_PARSER_CHECK([./input '0<0<0'], [1], [],
 AT_PARSER_CHECK([./input '0<0<0'], [1], [],

-         [syntax error, unexpected '<', expecting '<' or '>'
+         [syntax error, unexpected '<'

 ])
 
 AT_PARSER_CHECK([./input '0>0'])
 AT_PARSER_CHECK([./input '0>0>0'], [1], [],
 ])
 
 AT_PARSER_CHECK([./input '0>0'])
 AT_PARSER_CHECK([./input '0>0>0'], [1], [],

-         [syntax error, unexpected '>', expecting '<' or '>'
+         [syntax error, unexpected '>'

 ])
 
 AT_PARSER_CHECK([./input '0<0>0'], [1], [],
 ])
 
 AT_PARSER_CHECK([./input '0<0>0'], [1], [],

-         [syntax error, unexpected '>', expecting '<' or '>'
+         [syntax error, unexpected '>'
+])
+
+# We must disable default reductions in inconsistent states in order to
+# have an explicit list of all expected tokens.  (However, unless we use
+# canonical LR, lookahead sets are merged for different left contexts,
+# so it is still possible to have extra incorrect tokens in the expected
+# list.  That just doesn't happen to be a problem for this test case.)
+
+AT_BISON_CHECK([-Dlr.default-reductions=consistent -o input.c input.y])
+AT_COMPILE([input])
+
+AT_PARSER_CHECK([./input '0<0'])
+AT_PARSER_CHECK([./input '0<0<0'], [1], [],
+         [syntax error, unexpected '<', expecting $end
+])
+
+AT_PARSER_CHECK([./input '0>0'])
+AT_PARSER_CHECK([./input '0>0>0'], [1], [],
+         [syntax error, unexpected '>', expecting $end
+])
+
+AT_PARSER_CHECK([./input '0<0>0'], [1], [],
+         [syntax error, unexpected '>', expecting $end
+])
+
+AT_CLEANUP
+
+
+
+## ------------------------------------------- ##
+## parse.error=verbose and consistent errors.  ##
+## ------------------------------------------- ##
+
+AT_SETUP([[parse.error=verbose and consistent errors]])
+
+m4_pushdef([AT_CONSISTENT_ERRORS_CHECK], [
+
+AT_BISON_CHECK([$1[ -o input.c input.y]])
+AT_COMPILE([[input]])
+
+m4_pushdef([AT_EXPECTING], [m4_if($3, [ab], [[, expecting 'a' or 'b']],
+                                  $3, [a],  [[, expecting 'a']],
+                                  $3, [b],  [[, expecting 'b']])])
+
+AT_PARSER_CHECK([[./input]], [[1]], [],
+[[syntax error, unexpected ]$2[]AT_EXPECTING[
+]])
+
+m4_popdef([AT_EXPECTING])
+

 ])
 
 ])
 

+AT_DATA_GRAMMAR([input.y],
+[[%code {
+  #include <assert.h>
+  #include <stdio.h>
+  int yylex (void);
+  void yyerror (char const *);
+  #define USE(Var)
+}
+
+%define parse.error verbose
+
+// The point isn't to test IELR here, but state merging happens to
+// complicate the example.
+%define lr.type ielr
+
+%nonassoc 'a'
+
+// If yylval=0 here, then we know that the 'a' destructor is being
+// invoked incorrectly for the 'b' set in the semantic action below.
+// All 'a' tokens are returned by yylex, which sets yylval=1.
+%destructor {
+  if (!$$)
+    fprintf (stderr, "Wrong destructor.\n");
+} 'a'
+
+%%
+
+// The lookahead assigned by the semantic action isn't needed before
+// either error action is encountered.  In a previous version of Bison,
+// this was a problem as it meant yychar was not translated into yytoken
+// before either error action.  The second error action thus invoked a
+// destructor that it selected according to the incorrect yytoken.  The
+// first error action would have reported an incorrect unexpected token
+// except that, due to another bug, the unexpected token is not reported
+// at all because the error action is the default action in a consistent
+// state.  That bug still needs to be fixed.
+start: error-reduce consistent-error 'a' { USE ($3); } ;
+
+error-reduce:
+  'a' 'a' consistent-reduction consistent-error 'a'
+  { USE (($1, $2, $5)); }
+| 'a' error
+  { USE ($1); }
+;
+
+consistent-reduction: /*empty*/ {
+  assert (yychar == YYEMPTY);
+  yylval = 0;
+  yychar = 'b';
+} ;
+
+consistent-error:
+  'a' { USE ($1); }
+| /*empty*/ %prec 'a'
+;
+
+// Provide another context in which all rules are useful so that this
+// test case looks a little more realistic.
+start: 'b' consistent-error 'b' ;
+
+%%
+
+int
+yylex (void)
+{
+  static char const *input = "aa";
+  yylval = 1;
+  return *input++;
+}
+
+void
+yyerror (char const *msg)
+{
+  fprintf (stderr, "%s\n", msg);
+}
+
+int
+main (void)
+{
+  return yyparse ();
+}
+]])
+
+# See comments in grammar for why this test doesn't succeed.
+AT_XFAIL_IF([[:]])
+
+AT_CONSISTENT_ERRORS_CHECK([], [['b']], [[none]])
+AT_CONSISTENT_ERRORS_CHECK([[-Dlr.default-reductions=consistent]],
+                           [['b']], [[none]])
+
+# Canonical LR doesn't foresee the error for 'a'!
+AT_CONSISTENT_ERRORS_CHECK([[-Dlr.default-reductions=accepting]],
+                           [[$end]], [[a]])
+AT_CONSISTENT_ERRORS_CHECK([[-Flr.type=canonical-lr]], [[$end]], [[a]])
+
+m4_popdef([AT_CONSISTENT_ERRORS_CHECK])
+

 AT_CLEANUP
 
 
 AT_CLEANUP
 
 


@@ -134,7 +276,7 @@ AT_DATA([input.y],
 exp: exp OP exp | NUM;
 ]])
 
 exp: exp OP exp | NUM;
 ]])
 

-AT_CHECK([bison -o input.c --report=all input.y], 0, [],
+AT_BISON_CHECK([-o input.c --report=all input.y], 0, [],

 [input.y: conflicts: 1 shift/reduce
 ])
 
 [input.y: conflicts: 1 shift/reduce
 ])
 


@@ -214,7 +356,7 @@ state 4
 
 state 5
 
 
 state 5
 

-    1 exp: exp . OP exp  [$end, OP]
+    1 exp: exp . OP exp

     1    | exp OP exp .  [$end, OP]
 
     OP  shift, and go to state 4
     1    | exp OP exp .  [$end, OP]
 
     OP  shift, and go to state 4


@@ -242,7 +384,7 @@ AT_DATA([input.y],
 exp: exp OP exp | NUM;
 ]])
 
 exp: exp OP exp | NUM;
 ]])
 

-AT_CHECK([bison -o input.c --report=all input.y])
+AT_BISON_CHECK([-o input.c --report=all input.y])

 
 # Check the contents of the report.
 AT_CHECK([cat input.output], [],
 
 # Check the contents of the report.
 AT_CHECK([cat input.output], [],


@@ -317,7 +459,7 @@ state 4
 
 state 5
 
 
 state 5
 

-    1 exp: exp . OP exp  [$end, OP]
+    1 exp: exp . OP exp

     1    | exp OP exp .  [$end, OP]
 
     $default  reduce using rule 1 (exp)
     1    | exp OP exp .  [$end, OP]
 
     $default  reduce using rule 1 (exp)


@@ -328,6 +470,62 @@ state 5
 AT_CLEANUP
 
 
 AT_CLEANUP
 
 

+## ---------------------- ##
+## %precedence suffices.  ##
+## ---------------------- ##
+
+AT_SETUP([%precedence suffices])
+
+AT_DATA([input.y],
+[[%precedence "then"
+%precedence "else"
+%%
+stmt:
+  "if" cond "then" stmt
+| "if" cond "then" stmt "else" stmt
+| "stmt"
+;
+
+cond:
+  "exp"
+;
+]])
+
+AT_BISON_CHECK([-o input.c input.y])
+
+AT_CLEANUP
+
+
+## ------------------------------ ##
+## %precedence does not suffice.  ##
+## ------------------------------ ##
+
+AT_SETUP([%precedence does not suffice])
+
+AT_DATA([input.y],
+[[%precedence "then"
+%precedence "else"
+%%
+stmt:
+  "if" cond "then" stmt
+| "if" cond "then" stmt "else" stmt
+| "stmt"
+;
+
+cond:
+  "exp"
+| cond "then" cond
+;
+]])
+
+AT_BISON_CHECK([-o input.c input.y], 0, [],
+[[input.y: conflicts: 1 shift/reduce
+input.y:12.3-18: warning: rule useless in parser due to conflicts: cond: cond "then" cond
+]])
+
+AT_CLEANUP
+
+

 ## -------------------------------- ##
 ## Defaulted Conflicted Reduction.  ##
 ## -------------------------------- ##
 ## -------------------------------- ##
 ## Defaulted Conflicted Reduction.  ##
 ## -------------------------------- ##


@@ -364,14 +562,14 @@ id : '0';
 %%
 ]])
 
 %%
 ]])
 

-AT_CHECK([bison -o input.c --report=all input.y], 0, [],
+AT_BISON_CHECK([-o input.c --report=all input.y], 0, [],

 [[input.y: conflicts: 1 reduce/reduce
 [[input.y: conflicts: 1 reduce/reduce

-input.y:4.6-8: warning: rule never reduced because of conflicts: id: '0'
+input.y:4.6-8: warning: rule useless in parser due to conflicts: id: '0'

 ]])
 
 # Check the contents of the report.
 AT_CHECK([cat input.output], [],
 ]])
 
 # Check the contents of the report.
 AT_CHECK([cat input.output], [],

-[[Rules never reduced
+[[Rules useless in parser due to conflicts

 
     4 id: '0'
 
 
     4 id: '0'
 


@@ -481,7 +679,7 @@ AT_DATA([input.y],
 exp: exp OP exp | NUM;
 ]])
 
 exp: exp OP exp | NUM;
 ]])
 

-AT_CHECK([bison -o input.c input.y], 1, [],
+AT_BISON_CHECK([-o input.c input.y], 1, [],

 [input.y: conflicts: 1 shift/reduce
 input.y: expected 0 shift/reduce conflicts
 ])
 [input.y: conflicts: 1 shift/reduce
 input.y: expected 0 shift/reduce conflicts
 ])


@@ -501,7 +699,7 @@ AT_DATA([input.y],
 exp: exp OP exp | NUM;
 ]])
 
 exp: exp OP exp | NUM;
 ]])
 

-AT_CHECK([bison -o input.c input.y])
+AT_BISON_CHECK([-o input.c input.y])

 AT_CLEANUP
 
 
 AT_CLEANUP
 
 


@@ -518,16 +716,16 @@ AT_DATA([input.y],
 exp: exp OP exp | NUM;
 ]])
 
 exp: exp OP exp | NUM;
 ]])
 

-AT_CHECK([bison -o input.c input.y], 1, [],
+AT_BISON_CHECK([-o input.c input.y], 1, [],

 [input.y: conflicts: 1 shift/reduce
 input.y: expected 2 shift/reduce conflicts
 ])
 AT_CLEANUP
 
 
 [input.y: conflicts: 1 shift/reduce
 input.y: expected 2 shift/reduce conflicts
 ])
 AT_CLEANUP
 
 

-## ------------------------------ ##
-## %expect with reduce conflicts  ##
-## ------------------------------ ##
+## ------------------------------- ##
+## %expect with reduce conflicts.  ##
+## ------------------------------- ##

 
 AT_SETUP([%expect with reduce conflicts])
 
 
 AT_SETUP([%expect with reduce conflicts])
 


@@ -538,16 +736,33 @@ program: a 'a' | a a;
 a: 'a';
 ]])
 
 a: 'a';
 ]])
 

-AT_CHECK([bison -o input.c input.y], 1, [],
+AT_BISON_CHECK([-o input.c input.y], 1, [],

 [input.y: conflicts: 1 reduce/reduce
 input.y: expected 0 reduce/reduce conflicts
 ])
 AT_CLEANUP
 
 
 [input.y: conflicts: 1 reduce/reduce
 input.y: expected 0 reduce/reduce conflicts
 ])
 AT_CLEANUP
 
 

-## ------------------------------- ##
-## %no-default-prec without %prec  ##
-## ------------------------------- ##
+## ------------------------- ##
+## %prec with user strings.  ##
+## ------------------------- ##
+
+AT_SETUP([%prec with user string])
+
+AT_DATA([[input.y]],
+[[%%
+exp:
+  "foo" %prec "foo"
+;
+]])
+
+AT_BISON_CHECK([-o input.c input.y])
+AT_CLEANUP
+
+
+## -------------------------------- ##
+## %no-default-prec without %prec.  ##
+## -------------------------------- ##

 
 AT_SETUP([%no-default-prec without %prec])
 
 
 AT_SETUP([%no-default-prec without %prec])
 


@@ -565,15 +780,15 @@ e:   e '+' e
    ;
 ]])
 
    ;
 ]])
 

-AT_CHECK([bison -o input.c input.y], 0, [],
+AT_BISON_CHECK([-o input.c input.y], 0, [],

 [[input.y: conflicts: 4 shift/reduce
 ]])
 AT_CLEANUP
 
 
 [[input.y: conflicts: 4 shift/reduce
 ]])
 AT_CLEANUP
 
 

-## ---------------------------- ##
-## %no-default-prec with %prec  ##
-## ---------------------------- ##
+## ----------------------------- ##
+## %no-default-prec with %prec.  ##
+## ----------------------------- ##

 
 AT_SETUP([%no-default-prec with %prec])
 
 
 AT_SETUP([%no-default-prec with %prec])
 


@@ -591,13 +806,13 @@ e:   e '+' e %prec '+'
    ;
 ]])
 
    ;
 ]])
 

-AT_CHECK([bison -o input.c input.y])
+AT_BISON_CHECK([-o input.c input.y])

 AT_CLEANUP
 
 
 AT_CLEANUP
 
 

-## ---------------- ##
-## %default-prec    ##
-## ---------------- ##
+## --------------- ##
+## %default-prec.  ##
+## --------------- ##

 
 AT_SETUP([%default-prec])
 
 
 AT_SETUP([%default-prec])
 


@@ -615,7 +830,7 @@ e:   e '+' e
    ;
 ]])
 
    ;
 ]])
 

-AT_CHECK([bison -o input.c input.y])
+AT_BISON_CHECK([-o input.c input.y])

 AT_CLEANUP
 
 
 AT_CLEANUP
 
 


@@ -638,7 +853,7 @@ AT_DATA([[input.y]],
 
 start: resolved_conflict 'a' reported_conflicts 'a' ;
 
 
 start: resolved_conflict 'a' reported_conflicts 'a' ;
 

-/* S/R conflict resolved as shift, so the state with item
+/* S/R conflict resolved as reduce, so the state with item

  * (resolved_conflict: 'a' . unreachable1) and all it transition successors are
  * unreachable, and the associated production is useless.  */
 resolved_conflict:
  * (resolved_conflict: 'a' . unreachable1) and all it transition successors are
  * unreachable, and the associated production is useless.  */
 resolved_conflict:


@@ -667,19 +882,19 @@ reported_conflicts:
 
 ]])
 
 
 ]])
 

-AT_CHECK([[bison --report=all input.y]], 0, [],
+AT_BISON_CHECK([[--report=all input.y]], 0, [],

 [[input.y: conflicts: 1 shift/reduce, 1 reduce/reduce
 [[input.y: conflicts: 1 shift/reduce, 1 reduce/reduce

-input.y:12.5-20: warning: rule never reduced because of conflicts: resolved_conflict: 'a' unreachable1
-input.y:20.5-20: warning: rule never reduced because of conflicts: unreachable1: 'a' unreachable2
-input.y:21.4: warning: rule never reduced because of conflicts: unreachable1: /* empty */
-input.y:25.13: warning: rule never reduced because of conflicts: unreachable2: /* empty */
-input.y:25.16: warning: rule never reduced because of conflicts: unreachable2: /* empty */
-input.y:31.5-7: warning: rule never reduced because of conflicts: reported_conflicts: 'a'
-input.y:32.4: warning: rule never reduced because of conflicts: reported_conflicts: /* empty */
+input.y:12.5-20: warning: rule useless in parser due to conflicts: resolved_conflict: 'a' unreachable1
+input.y:20.5-20: warning: rule useless in parser due to conflicts: unreachable1: 'a' unreachable2
+input.y:21.4: warning: rule useless in parser due to conflicts: unreachable1: /* empty */
+input.y:25.13: warning: rule useless in parser due to conflicts: unreachable2: /* empty */
+input.y:25.16: warning: rule useless in parser due to conflicts: unreachable2: /* empty */
+input.y:31.5-7: warning: rule useless in parser due to conflicts: reported_conflicts: 'a'
+input.y:32.4: warning: rule useless in parser due to conflicts: reported_conflicts: /* empty */

 ]])
 
 AT_CHECK([[cat input.output]], 0,
 ]])
 
 AT_CHECK([[cat input.output]], 0,

-[[Rules never reduced
+[[Rules useless in parser due to conflicts

 
     2 resolved_conflict: 'a' unreachable1
 
 
     2 resolved_conflict: 'a' unreachable1
 


@@ -810,8 +1025,170 @@ state 6
 state 7
 
     1 start: resolved_conflict 'a' reported_conflicts 'a' .
 state 7
 
     1 start: resolved_conflict 'a' reported_conflicts 'a' .

- 
+

     $default  reduce using rule 1 (start)
 ]])
 
     $default  reduce using rule 1 (start)
 ]])
 

+AT_DATA([[input-keep.y]],
+[[%define lr.keep-unreachable-states
+]])
+AT_CHECK([[cat input.y >> input-keep.y]])
+
+AT_BISON_CHECK([[input-keep.y]], 0, [],
+[[input-keep.y: conflicts: 2 shift/reduce, 2 reduce/reduce
+input-keep.y:22.4: warning: rule useless in parser due to conflicts: unreachable1: /* empty */
+input-keep.y:26.16: warning: rule useless in parser due to conflicts: unreachable2: /* empty */
+input-keep.y:32.5-7: warning: rule useless in parser due to conflicts: reported_conflicts: 'a'
+input-keep.y:33.4: warning: rule useless in parser due to conflicts: reported_conflicts: /* empty */
+]])
+
+AT_CLEANUP
+
+
+## ------------------------------------------------------------ ##
+## Solved conflicts report for multiple reductions in a state.  ##
+## ------------------------------------------------------------ ##
+
+AT_SETUP([[Solved conflicts report for multiple reductions in a state]])
+
+# Used to lose earlier solved conflict messages even within a single S/R/R.
+
+AT_DATA([[input.y]],
+[[%left 'a'
+%right 'b'
+%right 'c'
+%right 'd'
+%%
+start:
+    'a'
+  | empty_a 'a'
+  | 'b'
+  | empty_b 'b'
+  | 'c'
+  | empty_c1 'c'
+  | empty_c2 'c'
+  | empty_c3 'c'
+  ;
+empty_a: %prec 'a' ;
+empty_b: %prec 'b' ;
+empty_c1: %prec 'c' ;
+empty_c2: %prec 'c' ;
+empty_c3: %prec 'd' ;
+]])
+AT_BISON_CHECK([[--report=all -o input.c input.y]], 0, [], [ignore])
+AT_CHECK([[cat input.output | sed -n '/^state 0$/,/^state 1$/p']], 0,
+[[state 0
+
+    0 $accept: . start $end
+    1 start: . 'a'
+    2      | . empty_a 'a'
+    3      | . 'b'
+    4      | . empty_b 'b'
+    5      | . 'c'
+    6      | . empty_c1 'c'
+    7      | . empty_c2 'c'
+    8      | . empty_c3 'c'
+    9 empty_a: .  ['a']
+   10 empty_b: .  []
+   11 empty_c1: .  []
+   12 empty_c2: .  []
+   13 empty_c3: .  ['c']
+
+    'b'  shift, and go to state 1
+
+    'c'       reduce using rule 13 (empty_c3)
+    $default  reduce using rule 9 (empty_a)
+
+    start     go to state 2
+    empty_a   go to state 3
+    empty_b   go to state 4
+    empty_c1  go to state 5
+    empty_c2  go to state 6
+    empty_c3  go to state 7
+
+    Conflict between rule 9 and token 'a' resolved as reduce (%left 'a').
+    Conflict between rule 10 and token 'b' resolved as shift (%right 'b').
+    Conflict between rule 11 and token 'c' resolved as shift (%right 'c').
+    Conflict between rule 12 and token 'c' resolved as shift (%right 'c').
+    Conflict between rule 13 and token 'c' resolved as reduce ('c' < 'd').
+
+
+state 1
+]])
+
+AT_CLEANUP
+
+
+## ------------------------------------------------------------ ##
+## %nonassoc error actions for multiple reductions in a state.  ##
+## ------------------------------------------------------------ ##
+
+# Used to abort when trying to resolve conflicts as %nonassoc error actions for
+# multiple reductions in a state.
+
+# For a %nonassoc error action token, used to print the first remaining
+# reduction on that token without brackets.
+
+AT_SETUP([[%nonassoc error actions for multiple reductions in a state]])
+
+AT_DATA([[input.y]],
+[[%nonassoc 'a' 'b' 'c'
+%%
+start:
+    'a'
+  | empty_a 'a'
+  | 'b'
+  | empty_b 'b'
+  | 'c'
+  | empty_c1 'c'
+  | empty_c2 'c'
+  | empty_c3 'c'
+  ;
+empty_a: %prec 'a' ;
+empty_b: %prec 'b' ;
+empty_c1: %prec 'c' ;
+empty_c2: %prec 'c' ;
+empty_c3: %prec 'c' ;
+]])
+
+AT_BISON_CHECK([[--report=all -o input.c input.y]], 0, [], [ignore])
+AT_CHECK([[cat input.output | sed -n '/^state 0$/,/^state 1$/p']], 0,
+[[state 0
+
+    0 $accept: . start $end
+    1 start: . 'a'
+    2      | . empty_a 'a'
+    3      | . 'b'
+    4      | . empty_b 'b'
+    5      | . 'c'
+    6      | . empty_c1 'c'
+    7      | . empty_c2 'c'
+    8      | . empty_c3 'c'
+    9 empty_a: .  []
+   10 empty_b: .  []
+   11 empty_c1: .  []
+   12 empty_c2: .  ['c']
+   13 empty_c3: .  ['c']
+
+    'a'  error (nonassociative)
+    'b'  error (nonassociative)
+    'c'  error (nonassociative)
+
+    'c'  [reduce using rule 12 (empty_c2)]
+    'c'  [reduce using rule 13 (empty_c3)]
+
+    start     go to state 1
+    empty_a   go to state 2
+    empty_b   go to state 3
+    empty_c1  go to state 4
+    empty_c2  go to state 5
+    empty_c3  go to state 6
+
+    Conflict between rule 9 and token 'a' resolved as an error (%nonassoc 'a').
+    Conflict between rule 10 and token 'b' resolved as an error (%nonassoc 'b').
+    Conflict between rule 11 and token 'c' resolved as an error (%nonassoc 'c').
+
+
+state 1
+]])

 AT_CLEANUP
 AT_CLEANUP