* Noteworthy changes in release ?.? (????-??-??) [?]
-** WARNING: Future backward-incompatibilities!
+** Java skeleton improvements
- Bison will stop adding a semicolon at the end of the actions (as announced
- in the release 2.5):
+ The Java skeleton now supports push parsing.
+ Contributed by Dennis Heimbigner.
- foo.y:2.22: warning: a ';' might be needed at the end of action code
- exp: "num" { $$ = $1 }
- ^
- foo.y:2.22: future versions of Bison will not add the ';'
+* Noteworthy changes in release 2.7.90 (2013-05-30) [beta]
+
+** WARNING: Future backward-incompatibilities!
Like other GNU packages, Bison will start using some of the C99 features
for its own code, especially the definition of variables after statements.
Support for YYLEX_PARAM and YYPARSE_PARAM is removed (deprecated in Bison
1.875): use %lex-param, %parse-param, or %param.
+ 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)
int yylex (YYSTYPE *yylval);
- This is has been fixed: yylval, yynerrs, yychar, and yylloc are now valid
+ This is fixed: yylval, yynerrs, yychar, and yylloc are now valid
identifiers for user-provided variables.
*** stdio.h is no longer needed when locations are enabled (yacc.c)
Changes in Bison 2.7 introduced a dependency on FILE and fprintf when
locations are enabled. This is fixed.
+*** Warnings about useless %pure-parser/%define api.pure are restored
+
** Diagnostics reported by Bison
Most of these features were contributed by Théophile Ranquet and Victor
activated by default. The old format can still be used by invoking Bison
with -fno-caret (or -fnone).
+ Some error messages that reproduced excerpts of the grammar are now using
+ the caret information only. For instance on:
+
+ %%
+ exp: 'a' | 'a';
+
+ Bison 2.7 reports:
+
+ in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
+ in.y:2.12-14: warning: rule useless in parser due to conflicts: exp: 'a' [-Wother]
+
+ Now bison reports:
+
+ in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
+ in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
+ exp: 'a' | 'a';
+ ^^^
+
+ and "bison -fno-caret" reports:
+
+ in.y: warning: 1 reduce/reduce conflict [-Wconflicts-rr]
+ in.y:2.12-14: warning: rule useless in parser due to conflicts [-Wother]
+
*** Enhancements of the -Werror option
The -Werror=CATEGORY option is now recognized, and will treat specified
bar.y: error: shift/reduce conflicts: 1 found, 0 expected
bar.y: error: reduce/reduce conflicts: 2 found, 0 expected
+** Incompatibilities with POSIX Yacc
+
+ The 'yacc' category is no longer part of '-Wall', enable it explicitly
+ with '-Wyacc'.
+
** Additional yylex/yyparse arguments
The new directive %param declares additional arguments to both yylex and
%param {arg1_type *arg1} {arg2_type *arg2}
+** Types of values for %define variables
+
+ Bison used to make no difference between '%define foo bar' and '%define
+ foo "bar"'. The former is now called a 'keyword value', and the latter a
+ 'string value'. A third kind was added: 'code values', such as '%define
+ foo {bar}'.
+
+ Keyword variables are used for fixed value sets, e.g.,
+
+ %define lr.type lalr
+
+ Code variables are used for value in the target language, e.g.,
+
+ %define api.value.type {struct semantic_type}
+
+ String variables are used remaining cases, e.g. file names.
+
** Variable api.token.prefix
The variable api.token.prefix changes the way tokens are identified in
with identifiers in the target language. For instance
%token FILE for ERROR
- %define api.token.prefix "TOK_"
+ %define api.token.prefix {TOK_}
%%
start: FILE for ERROR;
use these prefixed token names, although the grammar itself still
uses the short names (as in the sample rule given above).
+** Variable api.value.type
+
+ This new %define variable supersedes the #define macro YYSTYPE. The use
+ of YYSTYPE is discouraged. In particular, #defining YYSTYPE *and* either
+ using %union or %defining api.value.type results in undefined behavior.
+
+ Either define api.value.type, or use "%union":
+
+ %union
+ {
+ int ival;
+ char *sval;
+ }
+ %token <ival> INT "integer"
+ %token <sval> STRING "string"
+ %printer { fprintf (yyo, "%d", $$); } <ival>
+ %destructor { free ($$); } <sval>
+
+ /* In yylex(). */
+ yylval.ival = 42; return INT;
+ yylval.sval = "42"; return STRING;
+
+ The %define variable api.value.type supports both keyword and code values.
+
+ The keyword value 'union' means that the user provides genuine types, not
+ union member names such as "ival" and "sval" above (WARNING: will fail if
+ -y/--yacc/%yacc is enabled).
+
+ %define api.value.type union
+ %token <int> INT "integer"
+ %token <char *> STRING "string"
+ %printer { fprintf (yyo, "%d", $$); } <int>
+ %destructor { free ($$); } <char *>
+
+ /* In yylex(). */
+ yylval.INT = 42; return INT;
+ yylval.STRING = "42"; return STRING;
+
+ The keyword value variant is somewhat equivalent, but for C++ special
+ provision is made to allow classes to be used (more about this below).
+
+ %define api.value.type variant
+ %token <int> INT "integer"
+ %token <std::string> STRING "string"
+
+ Code values (in braces) denote user defined types. This is where YYSTYPE
+ used to be used.
+
+ %code requires
+ {
+ struct my_value
+ {
+ enum
+ {
+ is_int, is_string
+ } kind;
+ union
+ {
+ int ival;
+ char *sval;
+ } u;
+ };
+ }
+ %define api.value.type {struct my_value}
+ %token <u.ival> INT "integer"
+ %token <u.sval> STRING "string"
+ %printer { fprintf (yyo, "%d", $$); } <u.ival>
+ %destructor { free ($$); } <u.sval>
+
+ /* In yylex(). */
+ yylval.u.ival = 42; return INT;
+ yylval.u.sval = "42"; return STRING;
+
** Variable parse.error
This variable controls the verbosity of error messages. The use of the
It used to be an error only if used in non GLR mode, _and_ if there are
reduce/reduce conflicts.
-** Token numbering has changed to preserve the user-defined order
+** Tokens are numbered in their order of appearance
+
+ Contributed by Valentin Tolmer.
+
+ With '%token A B', A had a number less than the one of B. However,
+ precedence declarations used to generate a reversed order. This is now
+ fixed, and introducing tokens with any of %token, %left, %right,
+ %precedence, or %nonassoc yields the same result.
+
+ When mixing declarations of tokens with a litteral character (e.g., 'a')
+ or with an identifier (e.g., B) in a precedence declaration, Bison
+ numbered the litteral characters first. For example
+
+ %right A B 'c' 'd'
+
+ would lead to the tokens declared in this order: 'c' 'd' A B. Again, the
+ input order is now preserved.
- When declaring %token A B, the numbering for A is inferior to B. Up to now,
- when declaring associativity at the same time, with %left (or %right,
- %precedence, %nonassoc), B was inferior to A.
+ These changes were made so that one can remove useless precedence and
+ associativity declarations (i.e., map %nonassoc, %left or %right to
+ %precedence, or to %token) and get exactly the same output.
** Useless precedence and associativity
Contributed by Valentin Tolmer.
- When developping and maintaining a grammar, useless associativity and
+ When developing and maintaining a grammar, useless associativity and
precedence directives are common. They can be a nuisance: new ambiguities
arising are sometimes masked because their conflicts are resolved due to
the extra precedence or associativity information. Furthermore, it can
%left '*'
%%
exp:
- "num"
- | exp '+' "num"
+ "number"
+ | exp '+' "number"
| exp '*' exp
;
%precedence '='
%%
- exp: "var" '=' "num";
+ exp: "var" '=' "number";
will produce a
%nonassoc '='
%%
- exp: "var" '=' "num";
+ exp: "var" '=' "number";
The warning is:
%nonassoc '='
^^^
-** Java skeleton improvements
+** Empty rules
- Contributed by Paolo Bonzini.
+ With help from Joel E. Denny and Gabriel Rassoul.
+
+ Empty rules (i.e., with an empty right-hand side) can now be explicitly
+ marked by the new %empty directive. Using %empty on a non-empty rule is
+ an error. The new -Wempty-rule warning reports empty rules without
+ %empty. On the following grammar:
+
+ %%
+ s: a b c;
+ a: ;
+ b: %empty;
+ c: 'a' %empty;
+
+ bison reports:
+
+ 3.4-5: warning: empty rule without %empty [-Wempty-rule]
+ a: {}
+ ^^
+ 5.8-13: error: %empty on non-empty rule
+ c: 'a' %empty {};
+ ^^^^^^
+
+** Java skeleton improvements
The constants for token names were moved to the Lexer interface. Also, it
is possible to add code to the parser's constructors using "%code init"
and "%define init_throws".
+ Contributed by Paolo Bonzini.
** C++ skeletons improvements
;
list:
- /* nothing */ { /* Generates an empty string list */ }
+ %empty { /* Generates an empty string list. */ }
| list item ";" { std::swap ($$, $1); $$.push_back ($2); }
;
...
}
+*** C++ locations
+
+ There are operator- and operator-= for 'location'. Negative line/column
+ increments can no longer underflow the resulting value.
+
+* Noteworthy changes in release 2.7.1 (2013-04-15) [stable]
+
+** Bug fixes
+
+*** Fix compiler attribute portability (yacc.c)
+
+ With locations enabled, __attribute__ was used unprotected.
+
+*** Fix some compiler warnings (lalr1.cc)
+
* Noteworthy changes in release 2.7 (2012-12-12) [stable]
** Bug fixes
exp: exp '+' exp { $exp = $1 + $3; };
^^^
- The default behaviour for now is still not to display these unless
- explictly asked with -fcaret (or -fall). However, in a later release, it
+ The default behavior for now is still not to display these unless
+ explicitly asked with -fcaret (or -fall). However, in a later release, it
will be made the default behavior (but may still be deactivated with
-fno-caret).
Other issues in the test suite have been addressed.
- Nul characters are correctly displayed in error messages.
+ Null characters are correctly displayed in error messages.
When possible, yylloc is correctly initialized before calling yylex. It
is no longer necessary to initialize it in the %initial-action.
LocalWords: Automake TMPDIR LESSEQ ylwrap endif yydebug YYTOKEN YYLSP ival hh
LocalWords: extern YYTOKENTYPE TOKENTYPE yytokentype tokentype STYPE lval pdf
LocalWords: lang yyoutput dvi html ps POSIX lvalp llocp Wother nterm arg init
- LocalWords: TOK calc yyo fval Wconflicts
+ LocalWords: TOK calc yyo fval Wconflicts parsers yystackp yyval yynerrs
+ LocalWords: Théophile Ranquet Santet fno fnone stype associativity Tolmer
+ LocalWords: Wprecedence Rassoul Wempty Paolo Bonzini parser's Michiel loc
+ LocalWords: redeclaration sval fcaret reentrant XSLT xsl Wmaybe yyvsp Tedi
+ LocalWords: pragmas noreturn untyped Rozenman unexpanded Wojciech Polak
+ LocalWords: Alexandre MERCHANTABILITY yytype
Local Variables:
mode: outline
projects / bison.git / blobdiff