+** YYFAIL now produces warnings and Java parsers no longer implement it:
+
+ YYFAIL has existed for many years as an undocumented feature of
+ deterministic parsers in C generated by Bison. More recently, it was
+ a documented feature of Bison's experimental Java parsers. As
+ promised in Bison 2.4.2's NEWS entry, any appearance of YYFAIL in a
+ semantic action now produces a deprecation warning, and Java parsers
+ no longer implement YYFAIL at all. For further details, including a
+ discussion of how to suppress C preprocessor warnings about YYFAIL
+ being unused, see the Bison 2.4.2 NEWS entry.
+
+** Temporary hack for adding a semicolon to the user action:
+
+ Previously, Bison appended a semicolon to every user action for
+ reductions when the output language defaulted to C (specifically, when
+ neither %yacc, %language, %skeleton, or equivalent command-line
+ options were specified). This allowed actions such as
+
+ exp: exp "+" exp { $$ = $1 + $3 };
+
+ instead of
+
+ exp: exp "+" exp { $$ = $1 + $3; };
+
+ As a first step in removing this misfeature, Bison now issues a
+ warning when it appends a semicolon. Moreover, in cases where Bison
+ cannot easily determine whether a semicolon is needed (for example, an
+ action ending with a cpp directive or a braced compound initializer),
+ it no longer appends one. Thus, the C compiler might now complain
+ about a missing semicolon where it did not before. Future releases of
+ Bison will cease to append semicolons entirely.
+
+** Verbose syntax error message fixes:
+
+ When %error-verbose or the obsolete `#define YYERROR_VERBOSE' is
+ specified, syntax error messages produced by the generated parser
+ include the unexpected token as well as a list of expected tokens.
+ The effect of %nonassoc on these verbose messages has been corrected
+ in two ways, but a more complete fix requires LAC, described above:
+
+*** When %nonassoc is used, there can exist parser states that accept no
+ tokens, and so the parser does not always require a lookahead token
+ in order to detect a syntax error. Because no unexpected token or
+ expected tokens can then be reported, the verbose syntax error
+ message described above is suppressed, and the parser instead
+ reports the simpler message, `syntax error'. Previously, this
+ suppression was sometimes erroneously triggered by %nonassoc when a
+ lookahead was actually required. Now verbose messages are
+ suppressed only when all previous lookaheads have already been
+ shifted or discarded.
+
+*** Previously, the list of expected tokens erroneously included tokens
+ that would actually induce a syntax error because conflicts for them
+ were resolved with %nonassoc in the current parser state. Such
+ tokens are now properly omitted from the list.
+
+*** Expected token lists are still often wrong due to state merging
+ (from LALR or IELR) and default reductions, which can both add
+ invalid tokens and subtract valid tokens. Canonical LR almost
+ completely fixes this problem by eliminating state merging and
+ default reductions. However, there is one minor problem left even
+ when using canonical LR and even after the fixes above. That is,
+ if the resolution of a conflict with %nonassoc appears in a later
+ parser state than the one at which some syntax error is
+ discovered, the conflicted token is still erroneously included in
+ the expected token list. Bison's new LAC implementation,
+ described above, eliminates this problem and the need for
+ canonical LR. However, LAC is still experimental and is disabled
+ by default.
+
+** Java skeleton fixes:
+
+*** A location handling bug has been fixed.
+
+*** The top element of each of the value stack and location stack is now
+ cleared when popped so that it can be garbage collected.
+
+*** Parser traces now print the top element of the stack.
+
+** -W/--warnings fixes:
+
+*** Bison now properly recognizes the `no-' versions of categories:
+
+ For example, given the following command line, Bison now enables all
+ warnings except warnings for incompatibilities with POSIX Yacc:
+
+ bison -Wall,no-yacc gram.y
+
+*** Bison now treats S/R and R/R conflicts like other warnings:
+
+ Previously, conflict reports were independent of Bison's normal
+ warning system. Now, Bison recognizes the warning categories
+ `conflicts-sr' and `conflicts-rr'. This change has important
+ consequences for the -W and --warnings command-line options. For
+ example:
+
+ bison -Wno-conflicts-sr gram.y # S/R conflicts not reported
+ bison -Wno-conflicts-rr gram.y # R/R conflicts not reported
+ bison -Wnone gram.y # no conflicts are reported
+ bison -Werror gram.y # any conflict is an error
+
+ However, as before, if the %expect or %expect-rr directive is
+ specified, an unexpected number of conflicts is an error, and an
+ expected number of conflicts is not reported, so -W and --warning
+ then have no effect on the conflict report.
+
+*** The `none' category no longer disables a preceding `error':
+
+ For example, for the following command line, Bison now reports
+ errors instead of warnings for incompatibilities with POSIX Yacc:
+
+ bison -Werror,none,yacc gram.y
+
+*** The `none' category now disables all Bison warnings:
+
+ Previously, the `none' category disabled only Bison warnings for
+ which there existed a specific -W/--warning category. However,
+ given the following command line, Bison is now guaranteed to
+ suppress all warnings:
+
+ bison -Wnone gram.y
+
+** Precedence directives can now assign token number 0:
+
+ Since Bison 2.3b, which restored the ability of precedence
+ directives to assign token numbers, doing so for token number 0 has
+ produced an assertion failure. For example:
+
+ %left END 0
+
+ This bug has been fixed.
+
+* Changes in version 2.4.3 (2010-08-05):
+
+** Bison now obeys -Werror and --warnings=error for warnings about
+ grammar rules that are useless in the parser due to conflicts.
projects / bison.git / blobdiff