Re: new pacification suggestion?

> Le 20 nov. 2018 à 23:18, Akim Demaille <[email protected]> a écrit :
> 
> I don’t have any problems with having two pairs of parens, after all we’ve done that forever in the case of assignments in if’s etc.  That’s a clear way to tell the others, including the compiler, that something fishy is intentional (until ‘sic’ becomes a keyword).
> 
> The problem here is that it does not work, although it should.

This appears to be the proper fix.

commit cc050fd3218c4ee467dfe6c234867d84bd3e7119
Author: Akim Demaille <[email protected]>
Date:   Thu Nov 22 18:03:12 2018 +0100

    warning: avoid warnings about unreachable code
    
    Reported by Uxio Prego.
    https://lists.gnu.org/archive/html/help-bison/2018-11/msg00031.html
    
    We also need to move the unreachable 'goto' to a reachable place,
    otherwise clang complains about the code being unreachable anyway.
    See also https://bugs.llvm.org/show_bug.cgi?id=39736.
    
    Interestingly, we don't have to apply that trick to
    `#define YYCDEBUG if (false) std::cerr`, clang does not warn when the
    code comes from macro expansion.
    
    * configure.ac: Use -Wunreachable-code when supported.
    * data/lalr1.cc, data/yacc.c: Pacify clang's warning about `if (0)`
    by using a macro.
    Another possibility was to move this statement to a reachable place.
    * tests/actions.at, tests/c++.at: Avoid generating unreachable code.

diff --git a/configure.ac b/configure.ac
index 3d55f08c..959fc968 100644
--- a/configure.ac
+++ b/configure.ac
@@ -113,6 +113,7 @@ if test "$enable_gcc_warnings" = yes; then
     -fno-color-diagnostics
     -Wno-keyword-macro'
 
+
   AC_LANG_PUSH([C])
   # Clang supports many of GCC's -W options, but only issues warnings
   # on the ones it does not recognize.  In that case, gl_WARN_ADD
@@ -126,6 +127,11 @@ if test "$enable_gcc_warnings" = yes; then
   # CFLAGS, and restore CFLAGS after the tests.
   save_CFLAGS=$CFLAGS
   gl_WARN_ADD([-Werror=unknown-warning-option], [CFLAGS])
+  # Accept this warning only if it is not too touchy (e.g., clang 3.3
+  # and 3.4).
+  gl_WARN_ADD([-Wunreachable-code], [WARN_CFLAGS],
+              [AC_LANG_PROGRAM([],
+              [[if (sizeof (long) < sizeof (int)) return 1;]])])
   for i in $warn_common $warn_c;
   do
     gl_WARN_ADD([$i], [WARN_CFLAGS])
@@ -147,6 +153,7 @@ if test "$enable_gcc_warnings" = yes; then
   CFLAGS=$save_CFLAGS
   AC_LANG_POP([C])
 
+
   AC_LANG_PUSH([C++])
   save_CXXFLAGS=$CXXFLAGS
   gl_WARN_ADD([-Werror=unknown-warning-option], [CXXFLAGS])
@@ -154,6 +161,11 @@ if test "$enable_gcc_warnings" = yes; then
   do
     gl_WARN_ADD([$i], [WARN_CXXFLAGS])
   done
+  # Accept this warning only if it is not too touchy (e.g., clang 3.3
+  # and 3.4).
+  gl_WARN_ADD([-Wunreachable-code], [WARN_CXXFLAGS],
+              [AC_LANG_PROGRAM([],
+              [[if (sizeof (long) < sizeof (int)) return 1;]])])
   gl_WARN_ADD([-Wzero-as-null-pointer-constant], [WARN_CXXFLAGS],
               [AC_LANG_PROGRAM([], [nullptr])])
   gl_WARN_ADD([-Werror], [WERROR_CXXFLAGS])
diff --git a/data/lalr1.cc b/data/lalr1.cc
index 8486f9e8..78f3d1e0 100644
--- a/data/lalr1.cc
+++ b/data/lalr1.cc
@@ -971,11 +971,11 @@ b4_dollar_popdef])[]dnl
   | yyerrorlab -- error raised explicitly by YYERROR.  |
   `---------------------------------------------------*/
   yyerrorlab:
-    /* Pacify compilers like GCC when the user code never invokes
-       YYERROR and the label yyerrorlab therefore never appears in user
-       code.  */
+    /* Pacify compilers when the user code never invokes YYERROR and
+       the label yyerrorlab therefore never appears in user code.  */
     if (false)
-      goto yyerrorlab;
+      YYERROR;
+
     /* Do not reclaim the symbols of the rule whose action triggered
        this YYERROR.  */
     yypop_ (yylen);
diff --git a/data/yacc.c b/data/yacc.c
index 3f2883c6..ee0acd5b 100644
--- a/data/yacc.c
+++ b/data/yacc.c
@@ -1777,11 +1777,10 @@ yyerrlab:
 | yyerrorlab -- error raised explicitly by YYERROR.  |
 `---------------------------------------------------*/
 yyerrorlab:
-  /* Pacify compilers like GCC when the user code never invokes
-     YYERROR and the label yyerrorlab therefore never appears in user
-     code.  */
+  /* Pacify compilers when the user code never invokes YYERROR and the
+     label yyerrorlab therefore never appears in user code.  */
   if (0)
-    goto yyerrorlab;
+    YYERROR;
 
   /* Do not reclaim the symbols of the rule whose action triggered
      this YYERROR.  */
diff --git a/examples/calc++/local.mk b/examples/calc++/local.mk
index 059f2b05..8de5bf4d 100644
--- a/examples/calc++/local.mk
+++ b/examples/calc++/local.mk
@@ -20,7 +20,7 @@
 
 # Don't depend on $(BISON) otherwise we would rebuild these files
 # in srcdir, including during distcheck, which is forbidden.
-%D%/parser.stamp: $(BISON_IN)
+%D%/parser.stamp: $(BISON_IN) $(dist_pkgdata_DATA)
 SUFFIXES += .yy .stamp
 .yy.stamp:
 	$(AM_V_YACC)rm -f $@
diff --git a/tests/actions.at b/tests/actions.at
index deeed15d..7d692cd5 100644
--- a/tests/actions.at
+++ b/tests/actions.at
@@ -519,6 +519,8 @@ AT_DATA_GRAMMAR([[input.y]],
 #define RANGE(Location) ]AT_LALR1_CC_IF([(Location).begin.line, (Location).end.line],
       [(Location).first_line, (Location).last_line])[
 
+#define USE(SYM)
+
 /* Display the symbol type Symbol.  */
 #define V(Symbol, Value, Location, Sep) \
    fprintf (stderr, #Symbol " (%d@%d-%d)%s", Value, RANGE(Location), Sep)
@@ -610,8 +612,8 @@ input:
 ;
 
 check-spontaneous-errors:
-  raise         { abort(); $$ = $1; }
-| '(' raise ')' { abort(); $$ = $2; }
+  raise         { abort(); USE(($$, $1)); }
+| '(' raise ')' { abort(); USE(($$, $2)); }
 | error
   {
     $$ = 5;
diff --git a/tests/c++.at b/tests/c++.at
index 81c61863..2d5a4ac2 100644
--- a/tests/c++.at
+++ b/tests/c++.at
@@ -435,8 +435,6 @@ namespace yy
            return parser::token::TEXT;]])[
          }
     }
-
-    abort ();
   }
 }