cex: also include the counterexamples in the report

The report is the best place to show the details about
counterexamples, since we have the state right under the nose.

For instance:

State 7

    1 exp: exp . "⊕" exp
    2    | exp . "+" exp
    2    | exp "+" exp .  [$end, "+", "⊕"]
    3    | exp . "+" exp
    3    | exp "+" exp .  [$end, "+", "⊕"]

    "⊕"  shift, and go to state 6

    $end      reduce using rule 2 (exp)
    $end      [reduce using rule 3 (exp)]
    "+"       reduce using rule 2 (exp)
    "+"       [reduce using rule 3 (exp)]
    "⊕"       [reduce using rule 2 (exp)]
    "⊕"       [reduce using rule 3 (exp)]
    $default  reduce using rule 2 (exp)

    Conflict between rule 2 and token "+" resolved as reduce (%left "+").

    Shift/reduce conflict on token "⊕":
        2 exp: exp "+" exp .
        1 exp: exp . "⊕" exp
      Example                  exp "+" exp • "⊕" exp
      First derivation         exp ::=[ exp ::=[ exp "+" exp • ] "⊕" exp ]
      Example                  exp "+" exp • "⊕" exp
      Second derivation        exp ::=[ exp "+" exp ::=[ exp • "⊕" exp ] ]

    Reduce/reduce conflict on tokens $end, "+", "⊕":
        2 exp: exp "+" exp .
        3 exp: exp "+" exp .
      Example                  exp "+" exp •
      First derivation         exp ::=[ exp "+" exp • ]
      Example                  exp "+" exp •
      Second derivation        exp ::=[ exp "+" exp • ]

    Shift/reduce conflict on token "⊕":
        3 exp: exp "+" exp .
        1 exp: exp . "⊕" exp
      Example                  exp "+" exp • "⊕" exp
      First derivation         exp ::=[ exp ::=[ exp "+" exp • ] "⊕" exp ]
      Example                  exp "+" exp • "⊕" exp
      Second derivation        exp ::=[ exp "+" exp ::=[ exp • "⊕" exp ] ]

* src/conflicts.h, src/conflicts.c (has_conflicts): New.
* src/counterexample.h, src/counterexample.c (print_counterexample):
Add a `prefix` argument.
(counterexample_report_shift_reduce)
(counterexample_report_reduce_reduce): Show the items when there's a
prefix.
* src/state-item.h, src/state-item.c (print_state_item):
Add a `prefix` argument.
* src/derivation.h, src/derivation.c (derivation_print)
(derivation_print_leaves): Add a prefix argument.
* src/print.c (print_state): When -Wcex is enabled, show the
conflicts.
* tests/report.at: Adjust.

src/parse-simulation.c

@@ -19,13 +19,14 @@
 
 #include <config.h>
 
+#include "parse-simulation.h"
+
 #include <gl_linked_list.h>
 #include <gl_xlist.h>
 #include <stdlib.h>
 
 #include "lssi.h"
 #include "nullable.h"
-#include "parse-simulation.h"
 
 typedef struct parse_state
 {
@@ -595,9 +596,9 @@ print_parse_state (parse_state *ps)
   FILE *out = stderr;
   fprintf (out, "(size %zu depth %d rc %d)\n",
           ps->state_items.total_size, ps->depth, ps->reference_count);
-  print_state_item (ps->state_items.head_elt, out);
-  print_state_item (ps->state_items.tail_elt, out);
+  print_state_item (ps->state_items.head_elt, out, "");
+  print_state_item (ps->state_items.tail_elt, out, "");
   if (ps->derivs.total_size > 0)
-    derivation_print (ps->derivs.head_elt, out);
+    derivation_print (ps->derivs.head_elt, out, "");
   putc ('\n', out);
 }