api.value.type: use keyword/brace values

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index 3816fdd510dae9804d8f79a748582ed19daa3ed4..406521b9a9dfd0ca61761d156f5fa873b1c33623 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -23,6 +23,26 @@ GNU Bison NEWS
   Missing semicolons at the end of actions are no longer added (as announced
   in the release 2.5).
 
+*** Use of YACC='bison -y'
+
+  TL;DR: With Autoconf <= 2.69, pass -Wno-yacc to (AM_)YFLAGS if you use
+  Bison extensions.
+
+  Traditional Yacc generates 'y.tab.c' whatever the name of the input file.
+  Therefore Makefiles written for Yacc expect 'y.tab.c' (and possibly
+  'y.tab.h' and 'y.outout') to be generated from 'foo.y'.
+
+  To this end, for ages, AC_PROG_YACC, Autoconf's macro to look for an
+  implementation of Yacc, was using Bison as 'bison -y'.  While it does
+  ensure compatible output file names, it also enables warnings for
+  incompatibilities with POSIX Yacc.  In other words, 'bison -y' triggers
+  warnings for Bison extensions.
+
+  Autoconf 2.70+ fixes this incompatibility by using YACC='bison -o y.tab.c'
+  (which also generates 'y.tab.h' and 'y.output' when needed).
+  Alternatively, disable Yacc warnings by passing '-Wno-yacc' to your Yacc
+  flags (YFLAGS, or AM_YFLAGS with Automake).
+
 ** Bug fixes
 
 *** The epilogue is no longer affected by internal #defines (glr.c)
@@ -275,10 +295,11 @@ GNU Bison NEWS
     yylval.sval = "42"; return STRING;
 
   The %define variable api.value.type supports several special values.  The
-  value "union" means that the user provides genuine types, not union member
-  names such as "ival" and "sval" above.
+  keyword value 'union' means that the user provides genuine types, not
+  union member names such as "ival" and "sval" above (WARNING: will fail if
+  -y/--yacc/%yacc is enabled).
 
-    %define api.value.type "union"
+    %define api.value.type union
     %token <int> INT "integer"
     %token <char *> STRING "string"
     %printer { fprintf (yyo, "%d", $$); } <int>
@@ -288,15 +309,15 @@ GNU Bison NEWS
     yylval.INT = 42; return INT;
     yylval.STRING = "42"; return STRING;
 
-  The value "variant" is somewhat equivalent, but for C++ special provision
-  is made to allow classes to be used (more about this below).
+  The keyword value variant is somewhat equivalent, but for C++ special
+  provision is made to allow classes to be used (more about this below).
 
-    %define api.value.type "variant"
+    %define api.value.type variant
     %token <int> INT "integer"
     %token <std::string> STRING "string"
 
-  Any other name is a user type to use.  This is where YYSTYPE used to be
-  used.
+  Values between braces denote user defined types.  This is where YYSTYPE
+  used to be used.
 
     %code requires
     {
@@ -313,7 +334,7 @@ GNU Bison NEWS
         } u;
       };
     }
-    %define api.value.type "struct my_value"
+    %define api.value.type {struct my_value}
     %token <u.ival> INT "integer"
     %token <u.sval> STRING "string"
     %printer { fprintf (yyo, "%d", $$); } <u.ival>