Merge remote-tracking branch 'origin/maint'

[bison.git] / NEWS

diff --git a/NEWS b/NEWS
index fd51b61b61163388870c814ba33de6ac0f3e636e..e1373657b4993abb3e5959c197713f510e05bc75 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -2,19 +2,184 @@ GNU Bison NEWS
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 

-** Future changes:
+** Warnings about useless semantic types
+
+  Bison now warns about useless (uninhabited) semantic types.  Since
+  semantic types are not declared to Bison (they are defined in the opaque
+  %union structure), it is %printer/%destructor directives about useless
+  types that trigger the warning:
+
+    %token <type1> term
+    %type  <type2> nterm
+    %printer    {} <type1> <type3>
+    %destructor {} <type2> <type4>
+    %%
+    nterm: term { $$ = $1; };
+
+    3.28-34: warning: type <type3> is used, but is not associated to any symbol
+    4.28-34: warning: type <type4> is used, but is not associated to any symbol
+
+** Warnings about undeclared symbols
+
+  Bison used to raise an error for %printer and %destructor directives for
+  undefined symbols.
+
+    %printer    {} symbol1
+    %destructor {} symbol2
+    %%
+    exp: "a";
+
+  This is now only a warning.
+
+** Warnings about useless destructors or printers
+
+  Bison now warns about useless destructors or printers.  In the following
+  example, the printer for <type1>, and the destructor for <type2> are
+  useless: all symbols of <type1> (token1) already have a printer, and all
+  symbols of type <type2> (token2) already have a destructor.
+
+    %token <type1> token1
+           <type2> token2
+           <type3> token3
+           <type4> token4
+    %printer    {} token1 <type1> <type3>
+    %destructor {} token2 <type2> <type4>
+
+** Additional yylex/yyparse arguments
+
+  The new directive %param declares additional arguments to both yylex and
+  yyparse.  The %lex-param, %parse-param, and %param directives support one
+  or more arguments.  Instead of
+
+    %lex-param   {arg1_type *arg1}
+    %lex-param   {arg2_type *arg2}
+    %parse-param {arg1_type *arg1}
+    %parse-param {arg2_type *arg2}
+
+  one may now declare
+
+    %param {arg1_type *arg1} {arg2_type *arg2}
+
+** 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".
+
+** C++ skeleton improvements
+
+  The C++ parser features a syntax_error exception, which can be
+  thrown from the scanner or from user rules to raise syntax errors.
+  This facilitates reporting errors caught in sub-functions (e.g.,
+  rejecting too large integral literals from a conversion function
+  used by the scanner, or rejecting invalid combinations from a
+  factory invoked by the user actions).
+
+** Variable api.tokens.prefix
+
+  The variable api.tokens.prefix changes the way tokens are identified in
+  the generated files.  This is especially useful to avoid collisions
+  with identifiers in the target language.  For instance
+
+    %token FILE for ERROR
+    %define api.tokens.prefix "TOK_"
+    %%
+    start: FILE for ERROR;
+
+  will generate the definition of the symbols TOK_FILE, TOK_for, and
+  TOK_ERROR in the generated sources.  In particular, the scanner must
+  use these prefixed token names, although the grammar itself still
+  uses the short names (as in the sample rule given above).
+
+** Variable api.namespace
+
+  The "namespace" variable is renamed "api.namespace".  Backward
+  compatibility is ensured, but upgrading is recommended.
+
+** Variable parse.error
+
+  The variable error controls the verbosity of error messages.  The
+  use of the %error-verbose directive is deprecated in favor of
+  %define parse.error "verbose".
+
+** Semantic predicates
+
+  The new, experimental, semantic-predicate feature allows actions of
+  the form %?{ BOOLEAN-EXPRESSION }, which cause syntax errors (as for
+  YYERROR) if the expression evaluates to 0, and are evaluated immediately
+  in GLR parsers, rather than being deferred.  The result is that they
+  allow the programmer to prune possible parses based on the values of
+  runtime expressions.

 
 

-  The next major release will drop support for generating parsers in K&R C,
-  and remove the definition of yystype (removal announced since Bison
-  1.875).
+* Noteworthy changes in release ?.? (????-??-??) [?]
+
+** Future changes
+
+  The next major release of Bison will drop support for the following
+  deprecated features.  Please report disagreements to bug-bison@gnu.org.
+
+*** K&C parsers
+
+  Support for generating parsers in K&R C will be removed.  Parsers
+  generated for C supprt ISO C90, and are tested with ISO C99 and ISO C11
+  compilers.
+
+*** Features deprecated since Bison 1.875
+
+  The definitions of yystype and yyltype will be removed; use YYSTYPE and
+  YYLTYPE.
+
+  YYPARSE_PARAM and YYLEX_PARAM, deprecated in favor of %parse-param and
+  %lex-param, will no longer be supported.

 
 

-** Changes in regular C parsers (yacc.c):
+  Support for the preprocessor symbol YYERROR_VERBOSE will be removed, use
+  %error-verbose.

 
 

-*** The generated header is included
+*** The generated header will be included (yacc.c)

 
   Instead of duplicating the content of the generated header (definition of
 
   Instead of duplicating the content of the generated header (definition of

-  YYSTYPE, yyltype etc.), the generated parser now includes it, as was
-  already the case for GLR or C++ parsers.
+  YYSTYPE, yyparse declaration etc.), the generated parser will include it,
+  as is already the case for GLR or C++ parsers.  This change is deferred
+  because existing versions of ylwrap (e.g., Automake 1.12.1) do not support
+  it.
+
+** Headers
+
+*** Guards (yacc.c, glr.c, glr.cc)
+
+  The generated headers are now guarded, as is already the case for C++
+  parsers (lalr1.cc).  For intance, with --defines=foo.h:
+
+    #ifndef YY_FOO_H
+    # define YY_FOO_H
+    ...
+    #endif /* !YY_FOO_H  */
+
+*** New declarations (yacc.c, glr.c)
+
+  The generated header now declares yydebug and yyparse.  Both honor
+  --name-prefix=bar_, and yield
+
+    int bar_parse (void);
+
+  rather than
+
+    #define yyparse bar_parse
+    int yyparse (void);
+
+  in order to facilitate the inclusion of several parser headers inside a
+  single compilation unit.
+
+*** Exported symbols in C++
+
+  The symbols YYTOKEN_TABLE and YYERROR_VERBOSE, which were defined in the
+  header, are removed, as they prevent the possibility of including several
+  generated headers from a single compilation unit.
+
+*** YYLSP_NEEDED
+
+  For the same reasons, the undocumented and unused macro YYLSP_NEEDED is no
+  longer defined.

 
 * Noteworthy changes in release 2.5.1 (2012-06-05) [stable]
 
 
 * Noteworthy changes in release 2.5.1 (2012-06-05) [stable]
 


@@ -53,10 +218,10 @@ GNU Bison NEWS
   The header files such as "parser.hh", "location.hh", etc. used a constant
   name for preprocessor guards, for instance:
 
   The header files such as "parser.hh", "location.hh", etc. used a constant
   name for preprocessor guards, for instance:
 

-  #ifndef BISON_LOCATION_HH
-  # define BISON_LOCATION_HH
-  ...
-  #endif // !BISON_LOCATION_HH
+    #ifndef BISON_LOCATION_HH
+    # define BISON_LOCATION_HH
+    ...
+    #endif // !BISON_LOCATION_HH

 
   The inclusion guard is now computed from "PREFIX/FILE-NAME", where lower
   case characters are converted to upper case, and series of
 
   The inclusion guard is now computed from "PREFIX/FILE-NAME", where lower
   case characters are converted to upper case, and series of


@@ -64,10 +229,10 @@ GNU Bison NEWS
 
   With "bison -o lang++/parser.cc", "location.hh" would now include:
 
 
   With "bison -o lang++/parser.cc", "location.hh" would now include:
 

-  #ifndef YY_LANG_LOCATION_HH
-  # define YY_LANG_LOCATION_HH
-  ...
-  #endif // !YY_LANG_LOCATION_HH
+    #ifndef YY_LANG_LOCATION_HH
+    # define YY_LANG_LOCATION_HH
+    ...
+    #endif // !YY_LANG_LOCATION_HH

 
 *** C++ locations:
 
 
 *** C++ locations:
 


@@ -298,33 +463,33 @@ GNU Bison NEWS
   to use it.  If, for instance, your location structure has "first"
   and "last" members, instead of
 
   to use it.  If, for instance, your location structure has "first"
   and "last" members, instead of
 

-      # define YYLLOC_DEFAULT(Current, Rhs, N)                             \
-        do                                                                 \
-          if (N)                                                           \
-            {                                                              \
-              (Current).first = (Rhs)[1].location.first;                   \
-              (Current).last  = (Rhs)[N].location.last;                    \
-            }                                                              \
-          else                                                             \
-            {                                                              \
-              (Current).first = (Current).last = (Rhs)[0].location.last;   \
-            }                                                              \
-        while (false)
+    # define YYLLOC_DEFAULT(Current, Rhs, N)                             \
+      do                                                                 \
+        if (N)                                                           \
+          {                                                              \
+            (Current).first = (Rhs)[1].location.first;                   \
+            (Current).last  = (Rhs)[N].location.last;                    \
+          }                                                              \
+        else                                                             \
+          {                                                              \
+            (Current).first = (Current).last = (Rhs)[0].location.last;   \
+          }                                                              \
+      while (false)

 
   use:
 
 
   use:
 

-      # define YYLLOC_DEFAULT(Current, Rhs, N)                             \
-        do                                                                 \
-          if (N)                                                           \
-            {                                                              \
-              (Current).first = YYRHSLOC (Rhs, 1).first;                   \
-              (Current).last  = YYRHSLOC (Rhs, N).last;                    \
-            }                                                              \
-          else                                                             \
-            {                                                              \
-              (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last;   \
-            }                                                              \
-        while (false)
+    # define YYLLOC_DEFAULT(Current, Rhs, N)                             \
+      do                                                                 \
+        if (N)                                                           \
+          {                                                              \
+            (Current).first = YYRHSLOC (Rhs, 1).first;                   \
+            (Current).last  = YYRHSLOC (Rhs, N).last;                    \
+          }                                                              \
+        else                                                             \
+          {                                                              \
+            (Current).first = (Current).last = YYRHSLOC (Rhs, 0).last;   \
+          }                                                              \
+      while (false)

 
 ** YYLLOC_DEFAULT in C++:
 
 
 ** YYLLOC_DEFAULT in C++:
 


@@ -943,26 +1108,26 @@ GNU Bison NEWS
   if the symbols have destructors.  For instance:
 
      exp: exp "?" exp ":" exp { $1 ? $1 : $3; }
   if the symbols have destructors.  For instance:
 
      exp: exp "?" exp ":" exp { $1 ? $1 : $3; }

-       | exp "+" exp
-       ;
+        | exp "+" exp
+        ;

 
   will trigger a warning about $$ and $5 in the first rule, and $3 in
   the second ($1 is copied to $$ by the default rule).  This example
   most likely contains three errors, and could be rewritten as:
 
      exp: exp "?" exp ":" exp
 
   will trigger a warning about $$ and $5 in the first rule, and $3 in
   the second ($1 is copied to $$ by the default rule).  This example
   most likely contains three errors, and could be rewritten as:
 
      exp: exp "?" exp ":" exp

-           { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
-       | exp "+" exp
-           { $$ = $1 ? $1 : $3; if ($1) free ($3); }
-       ;
+            { $$ = $1 ? $3 : $5; free ($1 ? $5 : $3); free ($1); }
+        | exp "+" exp
+            { $$ = $1 ? $1 : $3; if ($1) free ($3); }
+        ;

 
   However, if the original actions were really intended, memory leaks
   and all, the warnings can be suppressed by letting Bison believe the
   values are used, e.g.:
 
      exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }
 
   However, if the original actions were really intended, memory leaks
   and all, the warnings can be suppressed by letting Bison believe the
   values are used, e.g.:
 
      exp: exp "?" exp ":" exp { $1 ? $1 : $3; (void) ($$, $5); }

-       | exp "+" exp         { $$ = $1; (void) $3; }
-       ;
+        | exp "+" exp         { $$ = $1; (void) $3; }
+        ;

 
   If there are mid-rule actions, the warning is issued if no action
   uses it.  The following triggers no warning: $1 and $3 are used.
 
   If there are mid-rule actions, the warning is issued if no action
   uses it.  The following triggers no warning: $1 and $3 are used.


@@ -1177,6 +1342,33 @@ GNU Bison NEWS
   - "parsing stack overflow..." -> "parser stack overflow"
     GLR parsers now report "parser stack overflow" as per the Bison manual.
 
   - "parsing stack overflow..." -> "parser stack overflow"
     GLR parsers now report "parser stack overflow" as per the Bison manual.
 

+** %parse-param and %lex-param
+  The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass
+  additional context to yyparse and yylex.  They suffer from several
+  shortcomings:
+
+  - a single argument only can be added,
+  - their types are weak (void *),
+  - this context is not passed to anciliary functions such as yyerror,
+  - only yacc.c parsers support them.
+
+  The new %parse-param/%lex-param directives provide a more precise control.
+  For instance:
+
+    %parse-param {int *nastiness}
+    %lex-param   {int *nastiness}
+    %parse-param {int *randomness}
+
+  results in the following signatures:
+
+    int yylex   (int *nastiness);
+    int yyparse (int *nastiness, int *randomness);
+
+  or, if both %pure-parser and %locations are used:
+
+    int yylex   (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
+    int yyparse (int *nastiness, int *randomness);
+

 ** Bison now warns if it detects conflicting outputs to the same file,
   e.g., it generates a warning for "bison -d -o foo.h foo.y" since
   that command outputs both code and header to foo.h.
 ** Bison now warns if it detects conflicting outputs to the same file,
   e.g., it generates a warning for "bison -d -o foo.h foo.y" since
   that command outputs both code and header to foo.h.


@@ -1206,16 +1398,16 @@ GNU Bison NEWS
   In agreement with POSIX and with other Yaccs, leaving a default
   action is valid when $$ is untyped, and $1 typed:
 
   In agreement with POSIX and with other Yaccs, leaving a default
   action is valid when $$ is untyped, and $1 typed:
 

-       untyped: ... typed;
+        untyped: ... typed;

 
   but the converse remains an error:
 
 
   but the converse remains an error:
 

-       typed: ... untyped;
+        typed: ... untyped;

 
 ** Values of mid-rule actions
   The following code:
 
 
 ** Values of mid-rule actions
   The following code:
 

-       foo: { ... } { $$ = $1; } ...
+        foo: { ... } { $$ = $1; } ...

 
   was incorrectly rejected: $1 is defined in the second mid-rule
   action, and is equal to the $$ of the first mid-rule action.
 
   was incorrectly rejected: $1 is defined in the second mid-rule
   action, and is equal to the $$ of the first mid-rule action.


@@ -1297,9 +1489,9 @@ GNU Bison NEWS
 ** Incorrect "Token not used"
   On a grammar such as
 
 ** Incorrect "Token not used"
   On a grammar such as
 

-           %token useless useful
-           %%
-           exp: '0' %prec useful;
+    %token useless useful
+    %%
+    exp: '0' %prec useful;

 
   where a token was used to set the precedence of the last rule,
   bison reported both "useful" and "useless" as useless tokens.
 
   where a token was used to set the precedence of the last rule,
   bison reported both "useful" and "useless" as useless tokens.


@@ -1318,9 +1510,9 @@ GNU Bison NEWS
   the user symbol is used in the reports, the graphs, and the verbose
   error messages instead of "$end", which remains being the default.
   For instance
   the user symbol is used in the reports, the graphs, and the verbose
   error messages instead of "$end", which remains being the default.
   For instance

-     %token MYEOF 0
+    %token MYEOF 0

   or
   or

-     %token MYEOF 0 "end of file"
+    %token MYEOF 0 "end of file"

 
 ** Semantic parser
   This old option, which has been broken for ages, is removed.
 
 ** Semantic parser
   This old option, which has been broken for ages, is removed.


@@ -1356,9 +1548,9 @@ GNU Bison NEWS
   Previous versions don't complain when there is a type clash on
   the default action if the rule has a mid-rule action, such as in:
 
   Previous versions don't complain when there is a type clash on
   the default action if the rule has a mid-rule action, such as in:
 

-      %type <foo> bar
-      %%
-      bar: '0' {} '0';
+    %type <foo> bar
+    %%
+    bar: '0' {} '0';

 
   This is fixed.
 
 
   This is fixed.