cex: don't display twice unifying examples if there is no color

[Akim Demaille]

commit 0f120354b623b10dc7e130f931348a030839cd75
Author: Akim Demaille <akim.demaille@gmail.com>
Date:   Fri Jun 19 07:06:24 2020 +0200

    cex: don't display twice unifying examples if there is no color
    
    It makes no sense, and is actually confusing, to display twice the
    same example with no visible difference.
    
    * src/complain.h, src/complain.c (is_styled): New.
    * src/counterexample.c (print_counterexample): Display the unified
    example a second time only if it makes a difference.
    * tests/conflicts.at, tests/counterexample.at, tests/report.at: Adjust.
    * tests/diagnostics.at: Make sure we do display the unifying examples
    twice when colors are enabled.  And check those colors.

diff --git a/src/complain.c b/src/complain.c
index 92d5fc52..889f0ae6 100644
--- a/src/complain.c
+++ b/src/complain.c
@@ -104,6 +104,23 @@ flush (FILE *out)
   fflush (out);
 }
 
+bool
+is_styled (FILE *out)
+{
+  if (out != stderr)
+    return false;
+  if (color_debug)
+    return true;
+#if HAVE_LIBTEXTSTYLE
+  return (color_mode == color_yes
+          || color_mode == color_html
+          || (color_mode == color_tty && isatty (STDERR_FILENO)));
+#else
+  return false;
+#endif
+}
+
+
 /*------------------------.
 | --warnings's handling.  |
 `------------------------*/
@@ -288,9 +305,7 @@ void
 complain_init_color (void)
 {
 #if HAVE_LIBTEXTSTYLE
-  if (color_mode == color_yes
-      || color_mode == color_html
-      || (color_mode == color_tty && isatty (STDERR_FILENO)))
+  if (is_styled (stderr))
     {
       style_file_prepare ("BISON_STYLE", "BISON_STYLEDIR", pkgdatadir (),
                           "bison-default.css");
diff --git a/src/complain.h b/src/complain.h
index eab5720d..303d0a54 100644
--- a/src/complain.h
+++ b/src/complain.h
@@ -36,6 +36,8 @@ void end_use_class (const char *style, FILE *out);
 /** Flush \a out.  */
 void flush (FILE *out);
 
+/** Whether there's styling on OUT.  */
+bool is_styled (FILE *out);
 
 /*-------------.
 | --warnings.  |
diff --git a/src/counterexample.c b/src/counterexample.c
index 01114fdf..e5b3a0af 100644
--- a/src/counterexample.c
+++ b/src/counterexample.c
@@ -27,6 +27,7 @@
 #include <gl_rbtreehash_list.h>
 #include <hash.h>
 #include <stdlib.h>
+#include <textstyle.h>
 #include <time.h>
 
 #include "closure.h"
@@ -109,9 +110,15 @@ print_counterexample (counterexample *cex, FILE *out, 
const char *prefix)
            prefix, _("First derivation"));
   derivation_print (cex->d1, out, prefix);
 
-  fprintf (out, "  %s%-20s ",
-           prefix, cex->unifying ? _("Example") : _("Second example"));
-  derivation_print_leaves (cex->d2, out, prefix);
+  // If we output to the terminal (via stderr) and we have color
+  // support, display unifying examples a second time, as color allows
+  // to see the differences.
+  if (!cex->unifying || is_styled (stderr))
+    {
+      fprintf (out, "  %s%-20s ",
+               prefix, cex->unifying ? _("Example") : _("Second example"));
+      derivation_print_leaves (cex->d2, out, prefix);
+    }
   fprintf (out, "  %s%-20s ",
            prefix, _("Second derivation"));
   derivation_print (cex->d2, out, prefix);
diff --git a/tests/conflicts.at b/tests/conflicts.at
index a3aadbff..95ab79df 100644
--- a/tests/conflicts.at
+++ b/tests/conflicts.at
@@ -763,7 +763,7 @@ AT_CLEANUP
 
 AT_SETUP([Unresolved SR Conflicts])
 
-AT_KEYWORDS([report])
+AT_KEYWORDS([cex report])
 
 AT_DATA([input.y],
 [[%token NUM OP
@@ -866,7 +866,6 @@ State 5
         1 exp: exp . OP exp
       Example                  exp OP exp . OP exp
       First derivation         exp ::=[ exp ::=[ exp OP exp . ] OP exp ]
-      Example                  exp OP exp . OP exp
       Second derivation        exp ::=[ exp OP exp ::=[ exp . OP exp ] ]
 
 ]])
@@ -1209,7 +1208,6 @@ State 1
         4 id: '0' .
       Example                  '0' .
       First derivation         exp ::=[ num ::=[ '0' . ] ]
-      Example                  '0' .
       Second derivation        exp ::=[ id ::=[ '0' . ] ]
 
 
@@ -1776,7 +1774,6 @@ State 5
         9 reported_conflicts: 'a' .
       Example                  'a' .
       First derivation         reported_conflicts ::=[ 'a' . ]
-      Example                  'a' .
       Second derivation        reported_conflicts ::=[ 'a' . ]
 
 
@@ -1961,7 +1958,6 @@ AT_CHECK([[cat input.output | sed -n '/^State 0$/,/^State 
1$/p']], 0,
        13 empty_c3: . %empty
       Example                  . 'c'
       First derivation         start ::=[ empty_c2 ::=[ . ] 'c' ]
-      Example                  . 'c'
       Second derivation        start ::=[ empty_c3 ::=[ . ] 'c' ]
 
 
diff --git a/tests/counterexample.at b/tests/counterexample.at
index 65dc03cc..48d5acf3 100644
--- a/tests/counterexample.at
+++ b/tests/counterexample.at
@@ -48,7 +48,6 @@ AT_BISON_CHECK_CEX([input.y], [], [],
 Shift/reduce conflict on token B:
   Example              A . B C
   First derivation     s ::=[ a ::=[ A . ] x ::=[ B C ] ]
-  Example              A . B C
   Second derivation    s ::=[ y ::=[ A . B ] c ::=[ C ] ]
 
 input.y:4.4: warning: rule useless in parser due to conflicts [-Wother]
@@ -78,7 +77,6 @@ AT_BISON_CHECK_CEX([input.y], [], [],
 Shift/reduce conflict on token B:
   Example              A . B C
   First derivation     s ::=[ a ::=[ A . ] bc ::=[ B C ] ]
-  Example              A . B C
   Second derivation    s ::=[ ac ::=[ A ac ::=[ b ::=[ . B ] ] C ] ]
 
 input.y:6.4: warning: rule useless in parser due to conflicts [-Wother]
@@ -109,7 +107,6 @@ AT_BISON_CHECK_CEX([input.y], [], [],
 Shift/reduce conflict on token B:
   Example              A . B
   First derivation     s ::=[ ax ::=[ A x ::=[ . ] ] by ::=[ B y ::=[ ] ] ]
-  Example              A . B
   Second derivation    s ::=[ A xby ::=[ . B ] ]
 
 Shift/reduce conflict on token B:
@@ -208,7 +205,6 @@ AT_BISON_CHECK_CEX([input.y], [], [],
 Shift/reduce conflict on token A:
   Example              b . A X X Y
   First derivation     a ::=[ r ::=[ b . ] t ::=[ A x ::=[ X ] xy ::=[ X Y ] ] 
]
-  Example              b . A X X Y
   Second derivation    a ::=[ s ::=[ b . xx ::=[ A X X ] y ::=[ Y ] ] ]
 
 Shift/reduce conflict on token X:
@@ -242,7 +238,6 @@ AT_BISON_CHECK_CEX([input.y], [], [],
 Reduce/reduce conflict on token $end:
   Example              A b .
   First derivation     a ::=[ A b . ]
-  Example              A b .
   Second derivation    a ::=[ A b ::=[ b . ] ]
 
 input.y:4.9: warning: rule useless in parser due to conflicts [-Wother]
@@ -331,7 +326,6 @@ AT_BISON_CHECK_CEX([input.y], [], [],
 Shift/reduce conflict on token B:
   Example              N A . B C
   First derivation     s ::=[ n ::=[ N a ::=[ A . ] B ] C ]
-  Example              N A . B C
   Second derivation    s ::=[ n ::=[ N b ::=[ A . B C ] ] ]
 
 input.y:5.4: warning: rule useless in parser due to conflicts [-Wother]
@@ -364,13 +358,11 @@ AT_BISON_CHECK_CEX([input.y], [], [],
 Reduce/reduce conflict on tokens b, c:
   Example              B . b c
   First derivation     S ::=[ B ::=[ A ::=[ B . ] b A ::=[ ] ] C ::=[ A ::=[ ] 
c A ::=[ ] ] ]
-  Example              B . b c
   Second derivation    S ::=[ B C ::=[ A ::=[ B ::=[ A ::=[ . ] b A ::=[ ] ] ] 
c A ::=[ ] ] ]
 
 Reduce/reduce conflict on tokens b, c:
   Example              C . c b
   First derivation     S ::=[ C ::=[ A ::=[ C . ] c A ::=[ ] ] B ::=[ A ::=[ ] 
b A ::=[ ] ] ]
-  Example              C . c b
   Second derivation    S ::=[ C B ::=[ A ::=[ C ::=[ A ::=[ . ] c A ::=[ ] ] ] 
b A ::=[ ] ] ]
 
 ]])
@@ -438,13 +430,11 @@ Shift/reduce conflict on token A:
 Reduce/reduce conflict on token $end:
   Example              b d .
   First derivation     a ::=[ b d . ]
-  Example              b d .
   Second derivation    a ::=[ b d ::=[ d . ] ]
 
 Reduce/reduce conflict on token $end:
   Example              c d .
   First derivation     a ::=[ c d . ]
-  Example              c d .
   Second derivation    a ::=[ c d ::=[ d . ] ]
 
 input.y:5.4: warning: rule useless in parser due to conflicts [-Wother]
@@ -476,7 +466,6 @@ AT_BISON_CHECK_CEX([input.y], [], [],
 Shift/reduce conflict on token J:
   Example              H i J . J J
   First derivation     s ::=[ a ::=[ H i ::=[ i J . ] J J ] ]
-  Example              H i J . J J
   Second derivation    s ::=[ a ::=[ H i J . J ] J ]
 
 input.y:5.13-15: warning: rule useless in parser due to conflicts [-Wother]
@@ -509,7 +498,6 @@ AT_BISON_CHECK_CEX([input.y], [], [],
 Shift/reduce conflict on token D:
   Example              A a . D
   First derivation     s ::=[ A a a ::=[ b ::=[ c ::=[ . ] ] ] d ::=[ D ] ]
-  Example              A a . D
   Second derivation    s ::=[ A a d ::=[ . D ] ]
 
 ]])
diff --git a/tests/diagnostics.at b/tests/diagnostics.at
index 035948c4..6d3ead97 100644
--- a/tests/diagnostics.at
+++ b/tests/diagnostics.at
@@ -49,15 +49,24 @@ if $EGREP ['\^M|\\[0-9][0-9][0-9]'] input.y experr 
>/dev/null; then
   AT_PERL_REQUIRE([-pi -e 's{\^M}{\r}g;s{\\(\d{3}|.)}{$v = $[]1; $v =~ 
/\A\d+\z/ ? chr($v) : $v}ge' input.y experr])
 fi
 
-AT_CHECK([LC_ALL="$locale" $5 bison -fcaret --color=debug -Wall input.y], 
[$3], [], [experr])
+AT_CHECK([LC_ALL="$locale" $5 bison -fcaret --color=debug -Wall,cex input.y], 
[$3], [], [experr])
 
 # When no style, same messages, but without style.
-AT_PERL_REQUIRE([-pi -e 's{(</?(-|\w)+>)}{ $[]1 eq "<tag>" ? $[]1 : "" }ge' 
experr])
+# Except for the second display of the counterexample,
+# which is not displayed at all.
+AT_PERL_REQUIRE([-pi -e '
+  s{(</?(-|\w)+>)}{ $[]1 eq "<tag>" ? $[]1 : "" }ge;
+  if (/Example/)
+    {
+      ++$example;
+      $_ = "" if $example % 2 == 0;
+    }
+' experr])
 
 # Cannot use AT_BISON_CHECK easily as we need to change the
 # environment.
 # FIXME: Enhance AT_BISON_CHECK.
-AT_CHECK([LC_ALL="$locale" $5 bison -fcaret -Wall input.y], [$3], [], [experr])
+AT_CHECK([LC_ALL="$locale" $5 bison -fcaret -Wall,cex input.y], [$3], [], 
[experr])
 
 
 AT_BISON_OPTION_POPDEFS
@@ -509,6 +518,41 @@ input.y:11.6-9: <error>error:</error> symbol 'QUUX' is 
used, but is not defined
 ]])
 
 
+## ----------------- ##
+## Counterexamples.  ##
+## ----------------- ##
+
+AT_TEST([[Counterexamples]],
+[[%expect 0
+%%
+exp
+: "if" exp "then" exp
+| "if" exp "then" exp "else" exp
+| exp "+" exp
+| "num"
+]],
+[1],
+[[input.y: <error>error:</error> shift/reduce conflicts: 4 found, 0 expected
+Shift/reduce conflict on token "+":
+  Example              <cex-0><cex-1><cex-leaf>exp</cex-leaf> 
<cex-leaf>"+"</cex-leaf> <cex-leaf>exp</cex-leaf> <cex-dot>•</cex-dot></cex-1> 
<cex-leaf>"+"</cex-leaf> <cex-leaf>exp</cex-leaf></cex-0>
+  First derivation     <cex-0><cex-step>exp ::=[ 
</cex-step><cex-1><cex-step>exp ::=[ </cex-step><cex-leaf>exp</cex-leaf> 
<cex-leaf>"+"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-dot>•</cex-dot><cex-step> ]</cex-step></cex-1> <cex-leaf>"+"</cex-leaf> 
<cex-leaf>exp</cex-leaf><cex-step> ]</cex-step></cex-0>
+  Example              <cex-0><cex-leaf>exp</cex-leaf> 
<cex-leaf>"+"</cex-leaf><cex-1> <cex-leaf>exp</cex-leaf> <cex-dot>•</cex-dot> 
<cex-leaf>"+"</cex-leaf> <cex-leaf>exp</cex-leaf></cex-1></cex-0>
+  Second derivation    <cex-0><cex-step>exp ::=[ 
</cex-step><cex-leaf>exp</cex-leaf> <cex-leaf>"+"</cex-leaf><cex-1> 
<cex-step>exp ::=[ </cex-step><cex-leaf>exp</cex-leaf> <cex-dot>•</cex-dot> 
<cex-leaf>"+"</cex-leaf> <cex-leaf>exp</cex-leaf><cex-step> 
]</cex-step></cex-1><cex-step> ]</cex-step></cex-0>
+
+Shift/reduce conflict on token "else":
+  Example              <cex-0><cex-leaf>"if"</cex-leaf> 
<cex-leaf>exp</cex-leaf> <cex-leaf>"then"</cex-leaf><cex-1> 
<cex-leaf>"if"</cex-leaf> <cex-leaf>exp</cex-leaf> <cex-leaf>"then"</cex-leaf> 
<cex-leaf>exp</cex-leaf> <cex-dot>•</cex-dot></cex-1> 
<cex-leaf>"else"</cex-leaf> <cex-leaf>exp</cex-leaf></cex-0>
+  First derivation     <cex-0><cex-step>exp ::=[ 
</cex-step><cex-leaf>"if"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-leaf>"then"</cex-leaf><cex-1> <cex-step>exp ::=[ 
</cex-step><cex-leaf>"if"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-leaf>"then"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-dot>•</cex-dot><cex-step> ]</cex-step></cex-1> <cex-leaf>"else"</cex-leaf> 
<cex-leaf>exp</cex-leaf><cex-step> ]</cex-step></cex-0>
+  Example              <cex-0><cex-leaf>"if"</cex-leaf> 
<cex-leaf>exp</cex-leaf> <cex-leaf>"then"</cex-leaf><cex-1> 
<cex-leaf>"if"</cex-leaf> <cex-leaf>exp</cex-leaf> <cex-leaf>"then"</cex-leaf> 
<cex-leaf>exp</cex-leaf> <cex-dot>•</cex-dot> <cex-leaf>"else"</cex-leaf> 
<cex-leaf>exp</cex-leaf></cex-1></cex-0>
+  Second derivation    <cex-0><cex-step>exp ::=[ 
</cex-step><cex-leaf>"if"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-leaf>"then"</cex-leaf><cex-1> <cex-step>exp ::=[ 
</cex-step><cex-leaf>"if"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-leaf>"then"</cex-leaf> <cex-leaf>exp</cex-leaf> <cex-dot>•</cex-dot> 
<cex-leaf>"else"</cex-leaf> <cex-leaf>exp</cex-leaf><cex-step> 
]</cex-step></cex-1><cex-step> ]</cex-step></cex-0>
+
+Shift/reduce conflict on token "+":
+  Example              <cex-0><cex-1><cex-leaf>"if"</cex-leaf> 
<cex-leaf>exp</cex-leaf> <cex-leaf>"then"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-leaf>"else"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-dot>•</cex-dot></cex-1> <cex-leaf>"+"</cex-leaf> 
<cex-leaf>exp</cex-leaf></cex-0>
+  First derivation     <cex-0><cex-step>exp ::=[ 
</cex-step><cex-1><cex-step>exp ::=[ </cex-step><cex-leaf>"if"</cex-leaf> 
<cex-leaf>exp</cex-leaf> <cex-leaf>"then"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-leaf>"else"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-dot>•</cex-dot><cex-step> ]</cex-step></cex-1> <cex-leaf>"+"</cex-leaf> 
<cex-leaf>exp</cex-leaf><cex-step> ]</cex-step></cex-0>
+  Example              <cex-0><cex-leaf>"if"</cex-leaf> 
<cex-leaf>exp</cex-leaf> <cex-leaf>"then"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-leaf>"else"</cex-leaf><cex-1> <cex-leaf>exp</cex-leaf> 
<cex-dot>•</cex-dot> <cex-leaf>"+"</cex-leaf> 
<cex-leaf>exp</cex-leaf></cex-1></cex-0>
+  Second derivation    <cex-0><cex-step>exp ::=[ 
</cex-step><cex-leaf>"if"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-leaf>"then"</cex-leaf> <cex-leaf>exp</cex-leaf> 
<cex-leaf>"else"</cex-leaf><cex-1> <cex-step>exp ::=[ 
</cex-step><cex-leaf>exp</cex-leaf> <cex-dot>•</cex-dot> 
<cex-leaf>"+"</cex-leaf> <cex-leaf>exp</cex-leaf><cex-step> 
]</cex-step></cex-1><cex-step> ]</cex-step></cex-0>
+
+]])
+
 
 
 
diff --git a/tests/report.at b/tests/report.at
index bc2e5dbb..1d93f9a5 100644
--- a/tests/report.at
+++ b/tests/report.at
@@ -1173,25 +1173,21 @@ input.y: warning: 3 reduce/reduce conflicts 
[-Wconflicts-rr]
 Shift/reduce conflict on token "⊕":
   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, "+", "⊕":
   Example              exp "+" exp •
   First derivation     exp ::=[ exp "+" exp • ]
-  Example              exp "+" exp •
   Second derivation    exp ::=[ exp "+" exp • ]
 
 Shift/reduce conflict on token "⊕":
   Example              exp "+" exp • "⊕" exp
   First derivation     exp ::=[ exp ::=[ exp "+" exp • ] "⊕" exp ]
-  Example              exp "+" exp • "⊕" exp
   Second derivation    exp ::=[ exp "+" exp ::=[ exp • "⊕" exp ] ]
 
 Shift/reduce conflict on token "⊕":
   Example              exp "⊕" exp • "⊕" exp
   First derivation     exp ::=[ exp ::=[ exp "⊕" exp • ] "⊕" exp ]
-  Example              exp "⊕" exp • "⊕" exp
   Second derivation    exp ::=[ exp "⊕" exp ::=[ exp • "⊕" exp ] ]
 
 input.y:6.3-13: warning: rule useless in parser due to conflicts [-Wother]
@@ -1342,7 +1338,6 @@ State 7
         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, "+", "⊕":
@@ -1350,7 +1345,6 @@ State 7
         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 "⊕":
@@ -1358,7 +1352,6 @@ State 7
         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 ] ]
 
 
@@ -1382,7 +1375,6 @@ State 8
         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 ] ]
 
 ]])