bison-1.875: yyerror() declaration and C++ compilation error

[Nelson H. F. Beebe]

After getting bison-1.875 installed on more than a dozen local systems
earlier today, I returned to work on a program that uses a yacc/bison
grammar.  On most systems, I compile this C code using C++ compilers,
to obtain stricter type checking and wider compiler testing.

Unfortunately, the bison upgrade has introduced a problem: I now get
errors like this on every system:

        % yacc --version
        bison (GNU Bison) 1.875
        ...

        % yacc -d hoc.y
        % g++ ... -c hoc.c
        y.tab.c: In function `int yyparse()':
        y.tab.c:2628: `yyerror' undeclared (first use this function)
        y.tab.c:2628: (Each undeclared identifier is reported only once for each
           function it appears in.)
        y.tab.c:2676: parse error before `goto'
        hoc.y: In function `void yyerror(char*)':
        hoc.y:1982: `void yyerror(char*)' used prior to declaration

A check of the bison manual shows that yyerror() is now expected to be
declared by the user: I don't see why that should be necessary since
bison itself generates calls to it, and thus should provide a suitable
prototype.  That prototype will isolate user code from possible future
changes in yyerror()'s interface.  [I note that the manual shows a
two-argument form for yyerror() when GLR parsing is selected; however,
when I inserted a %glr-parser directive, bison still produced the
one-argument form.]

So, I changed my grammar file to have in the preamble this prototype:

        #if defined(YYBISON)
        #define YYCONST const
        void yyerror (YYCONST char *);
        #endif /* defined(YYBISON) */

Compilation with gcc then succeeds, but compilation with g++ fails in
this code section:

        yyerrlab1:

          /* Suppress GCC warning that yyerrlab1 is unused when no action
             invokes YYERROR.  */
        #if defined (__GNUC_MINOR__) && 2093 <= (__GNUC__ * 1000 + 
__GNUC_MINOR__)
          __attribute__ ((__unused__))
        #endif

          goto yyerrlab2;

with the message "parse error before goto".

An additional check in the installed yacc.c file is needed:

        #if defined (__GNUC_MINOR__) && 2093 <= (__GNUC__ * 1000 + 
__GNUC_MINOR__) && !define(__GNUG__)
but perhaps there is a cleaner way.

Incidentally, I view it a very bad idea to install bison under the
name yacc as well: that masks access to the native yacc when that may
be what the user intended.  I hope that that change in bison will be
reconsidered.  I routinely test my parsers with bison, (native) yacc,
and Berkeley yacc, so that I can ensure that my grammars work with all
of them.  I'm strongly inclined to remove the installed
/usr/local/bin/yacc script on our systems.

Comments?

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- Nelson H. F. Beebe                    Tel: +1 801 581 5254                  -
- Center for Scientific Computing       FAX: +1 801 581 4148                  -
- University of Utah                    Internet e-mail: address@hidden  -
- Department of Mathematics, 110 LCB        address@hidden  address@hidden -
- 155 S 1400 E RM 233                       address@hidden                    -
- Salt Lake City, UT 84112-0090, USA    URL: http://www.math.utah.edu/~beebe  -
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