* Changes in version 2.4.2 (2010-03-20):
** Some portability problems that resulted in failures and livelocks
in the test suite on some versions of at least Solaris, AIX, HP-UX,
RHEL4, and Tru64 have been addressed. As a result, fatal Bison
errors should no longer cause M4 to report a broken pipe on the
affected platforms.
** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately.
POSIX specifies that an error be reported for any identifier that does
not appear on the LHS of a grammar rule and that is not defined by
%token, %left, %right, or %nonassoc. Bison 2.3b and later lost this
error report for the case when an identifier appears only after a
%prec directive. It is now restored. However, for backward
compatibility with recent Bison releases, it is only a warning for
now. In Bison 2.5 and later, it will return to being an error.
** Detection of GNU M4 1.4.6 or newer during configure is improved.
** Warnings from gcc's -Wundef option about undefined YYENABLE_NLS,
YYLTYPE_IS_TRIVIAL, and __STRICT_ANSI__ in C/C++ parsers are now
avoided.
** %code is now a permanent feature.
A traditional Yacc prologue directive is written in the form:
%{CODE%}
To provide a more flexible alternative, Bison 2.3b introduced the
%code directive with the following forms for C/C++:
%code {CODE}
%code requires {CODE}
%code provides {CODE}
%code top {CODE}
These forms are now considered permanent features of Bison. See the
%code entries in the section "Bison Declaration Summary" in the Bison
manual for a summary of their functionality. See the section
"Prologue Alternatives" for a detailed discussion including the
advantages of %code over the traditional Yacc prologue directive.
Bison's Java feature as a whole including its current usage of %code
is still considered experimental.
** YYFAIL is deprecated and will eventually be removed.
YYFAIL has existed for many years as an undocumented feature of
deterministic parsers in C generated by Bison. Previously, it was
documented for Bison's experimental Java parsers. YYFAIL is no longer
documented for Java parsers and is formally deprecated in both cases.
Users are strongly encouraged to migrate to YYERROR, which is
specified by POSIX.
Like YYERROR, you can invoke YYFAIL from a semantic action in order to
induce a syntax error. The most obvious difference from YYERROR is
that YYFAIL will automatically invoke yyerror to report the syntax
error so that you don't have to. However, there are several other
subtle differences between YYERROR and YYFAIL, and YYFAIL suffers from
inherent flaws when %error-verbose or `#define YYERROR_VERBOSE' is
used. For a more detailed discussion, see:
http://lists.gnu.org/archive/html/bison-patches/2009-12/msg00024.html
The upcoming Bison 2.5 will remove YYFAIL from Java parsers, but
deterministic parsers in C will continue to implement it. However,
because YYFAIL is already flawed, it seems futile to try to make new
Bison features compatible with it. Thus, during parser generation,
Bison 2.5 will produce a warning whenever it discovers YYFAIL in a
rule action. In a later release, YYFAIL will be disabled for
%error-verbose and `#define YYERROR_VERBOSE'. Eventually, YYFAIL will
be removed altogether.
There exists at least one case where Bison 2.5's YYFAIL warning will
be a false positive. Some projects add phony uses of YYFAIL and other
Bison-defined macros for the sole purpose of suppressing C
preprocessor warnings (from GCC cpp's -Wunused-macros, for example).
To avoid Bison's future warning, such YYFAIL uses can be moved to the
epilogue (that is, after the second `%%') in the Bison input file. In
this release (2.4.2), Bison already generates its own code to suppress
C preprocessor warnings for YYFAIL, so projects can remove their own
phony uses of YYFAIL if compatibility with Bison releases prior to
2.4.2 is not necessary.
** Internationalization.
Fix a regression introduced in Bison 2.4: Under some circumstances,
message translations were not installed although supported by the
host system.
586797c750