* Noteworthy changes in release 3.8.1 (2021-09-11) [stable]
The generation of prototypes for yylex and yyerror in Yacc mode is
breaking existing grammar files. To avoid breaking too many grammars, the
prototypes are now generated when `-y/--yacc` is used *and* the
`POSIXLY_CORRECT` environment variable is defined.
Avoid using `-y`/`--yacc` simply to comply with Yacc's file name
conventions, rather, use `-o y.tab.c`. Autoconf's AC_PROG_YACC macro uses
`-y`. Avoid it if possible, for instance by using gnulib's gl_PROG_BISON.
* Noteworthy changes in release 3.8 (2021-09-07) [stable]
** Backward incompatible changes
In conformance with the recommendations of the Graphviz team
(https://marc.info/?l=graphviz-devel&m=129418103126092), `-g`/`--graph`
now generates a *.gv file by default, instead of *.dot. A transition
started in Bison 3.4.
To comply with the latest POSIX standard, in Yacc compatibility mode
(options `-y`/`--yacc`) Bison now generates prototypes for yyerror and
yylex. In some situations, this is breaking compatibility: if the user
has already declared these functions but with some differences (e.g., to
declare them as static, or to use specific attributes), the generated
parser will fail to compile. To disable these prototypes, #define yyerror
(to `yyerror`), and likewise for yylex.
** Deprecated features
Support for the YYPRINT macro is removed. It worked only with yacc.c and
only for tokens. It was obsoleted by %printer, introduced in Bison 1.50
(November 2002).
It has always been recommended to prefer `%define api.value.type foo` to
`#define YYSTYPE foo`. The latter is supported in C for compatibility
with Yacc, but not in C++. Warnings are now issued if `#define YYSTYPE`
is used in C++, and eventually support will be removed.
In C++ code, prefer value_type to semantic_type to denote the semantic
value type, which is specified by the `api.value.type` %define variable.
** New features
*** A skeleton for the D programming language
The "lalr1.d" skeleton is now officially part of Bison.
It was originally contributed by Oliver Mangold, based on Paolo Bonzini's
lalr1.java, and was improved by H. S. Teoh. Adela Vais then took over
maintenance and invested a lot of efforts to complete, test and document
it.
It now supports all the bells and whistles of the other deterministic
parsers, which include: pull/push interfaces, verbose and custom error
messages, lookahead correction, token constructors, internationalization,
locations, printers, token and symbol prefixes, etc.
Two examples demonstrate the D parsers: a basic one (examples/d/simple),
and an advanced one (examples/d/calc).
*** Option -H, --header and directive %header
The option `-H`/`--header` supersedes the option `--defines`, and the
directive %header supersedes %defines. Both `--defines` and `%defines`
are, of course, maintained for backward compatibility.
*** Option --html
Since version 2.4 Bison can be used to generate HTML reports. However it
was a two-step process: first bison must be invoked with option `--xml`,
and then xsltproc must be run to the convert the XML reports into HTML.
The new option `--html` combines these steps. The xsltproc program must
be available.
*** A C++ native GLR parser
A new version of the C++ GLR parser was added: "glr2.cc". It generates
"true C++11", instead of a C++ wrapper around a C parser as does the
existing "glr.cc" parser. As a first significant consequence, it supports
`%define api.value.type variant`, contrary to glr.cc.
It should be upward compatible in terms of interface, feature and
performance to "glr.cc". To try it out, simply use
%skeleton "glr2.cc"
It will eventually replace "glr.cc". However we need user feedback on
this skeleton. _Please_ report your results and comments about it.
*** Counterexamples
Counterexamples now show the rule numbers, and always show ε for rules
with an empty right-hand side. For instance
exp
↳ 1: e1 e2 "a"
↳ 3: ε • ↳ 1: ε
instead of
exp
↳ e1 e2 "a"
↳ • ↳ ε
*** Lookahead correction in Java
The Java skeleton (lalr1.java) now supports LAC, via the `parse.lac`
%define variable.
*** Abort parsing for memory exhaustion (C)
User actions may now use `YYNOMEM` (similar to `YYACCEPT` and `YYABORT`)
to abort the current parse with memory exhaustion.
*** Printing locations in debug traces (C)
The `YYLOCATION_PRINT(File, Loc)` macro prints a location. It is defined
when (i) locations are enabled, (ii) the default type for locations is
used, (iii) debug traces are enabled, and (iv) `YYLOCATION_PRINT` is not
already defined.
Users may define `YYLOCATION_PRINT` to cover other cases.
*** GLR traces
There were no debug traces for deferred calls to user actions. They are
logged now.
* Noteworthy changes in release 3.7.6 (2021-03-08) [stable]
** Bug fixes
*** Reused Push Parsers
When a push-parser state structure is used for multiple parses, it was
possible for some state to leak from one run into the following one.
*** Fix Table Generation
In some very rare conditions, when there are many useless tokens, it was
possible to generate incorrect parsers.
* Noteworthy changes in release 3.7.5 (2021-01-24) [stable]
** Bug fixes
*** Counterexample Generation
In some cases counterexample generation could crash. This is fixed.
*** Fix Table Generation
In some very rare conditions, when there are many useless tokens, it was
possible to generate incorrect parsers.
*** GLR parsers now support %merge together with api.value.type=union.
*** C++ parsers use noexcept in more places.
*** Generated parsers avoid some warnings about signedness issues.
*** C-language parsers now avoid warnings from pedantic clang.
*** C-language parsers now work around quirks of HP-UX 11.23 (2003).
* Noteworthy changes in release 3.7.4 (2020-11-14) [stable]
** Bug fixes
*** Bug fixes in yacc.c
In Yacc mode, all the tokens are defined twice: once as an enum, and then
as a macro. YYEMPTY was missing its macro.
*** Bug fixes in lalr1.cc
The lalr1.cc skeleton used to emit internal assertions (using YY_ASSERT)
even when the `parse.assert` %define variable is not enabled. It no
longer does.
The private internal macro YY_ASSERT now obeys the `api.prefix` %define
variable.
When there is a very large number of tokens, some assertions could be long
enough to hit arbitrary limits in Visual C++. They have been rewritten to
work around this limitation.
** Changes
The YYBISON macro in generated "regular C parsers" (from the "yacc.c"
skeleton) used to be defined to 1. It is now defined to the version of
Bison as an integer (e.g., 30704 for version 3.7.4).
* Noteworthy changes in release 3.7.3 (2020-10-13) [stable]
** Bug fixes
Fix concurrent build issues.
The bison executable is no longer linked uselessly against libreadline.
Fix incorrect use of yytname in glr.cc.
* Noteworthy changes in release 3.7.2 (2020-09-05) [stable]
This release of Bison fixes all known bugs reported for Bison in MITRE's
Common Vulnerabilities and Exposures (CVE) system. These vulnerabilities
are only about bison-the-program itself, not the generated code.
Although these bugs are typically irrelevant to how Bison is used, they
are worth fixing if only to give users peace of mind.
There is no known vulnerability in the generated parsers.
** Bug fixes
Fix concurrent build issues (introduced in Bison 3.5).
Push parsers always use YYMALLOC/YYFREE (no direct calls to malloc/free).
Fix portability issues of the test suite, and of bison itself.
Some unlikely crashes found by fuzzing have been fixed. This is only
about bison itself, not the generated parsers.
* Noteworthy changes in release 3.7.1 (2020-08-02) [stable]
** Bug fixes
Crash when a token alias contains a NUL byte.
Portability issues with libtextstyle.
Portability issues of Bison itself with MSVC.
** Changes
Improvements and fixes in the documentation.
More precise location about symbol type redefinitions.
* Noteworthy changes in release 3.7 (2020-07-23) [stable]
** Deprecated features
The YYPRINT macro, which works only with yacc.c and only for tokens, was
obsoleted long ago by %printer, introduced in Bison 1.50 (November 2002).
It is deprecated and its support will be removed eventually.
In conformance with the recommendations of the Graphviz team, in the next
version Bison the option `--graph` will generate a *.gv file by default,
instead of *.dot. A transition started in Bison 3.4.
** New features
*** Counterexample Generation
Contributed by Vincent Imbimbo.
When given `-Wcounterexamples`/`-Wcex`, bison will now output
counterexamples for conflicts.
**** Unifying Counterexamples
Unifying counterexamples are strings which can be parsed in two ways due
to the conflict. For example on a grammar that contains the usual
"dangling else" ambiguity:
$ bison else.y
else.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
else.y: note: rerun with option '-Wcounterexamples' to generate conflict counterexamples
$ bison else.y -Wcex
else.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
else.y: warning: shift/reduce conflict on token "else" [-Wcounterexamples]
Example: "if" exp "then" "if" exp "then" exp • "else" exp
Shift derivation
exp
↳ "if" exp "then" exp
↳ "if" exp "then" exp • "else" exp
Example: "if" exp "then" "if" exp "then" exp • "else" exp
Reduce derivation
exp
↳ "if" exp "then" exp "else" exp
↳ "if" exp "then" exp •
When text styling is enabled, colors are used in the examples and the
derivations to highlight the structure of both analyses. In this case,
"if" exp "then" [ "if" exp "then" exp • ] "else" exp
vs.
"if" exp "then" [ "if" exp "then" exp • "else" exp ]
The counterexamples are "focused", in two different ways. First, they do
not clutter the output with all the derivations from the start symbol,
rather they start on the "conflicted nonterminal". They go straight to the
point. Second, they don't "expand" nonterminal symbols uselessly.
**** Nonunifying Counterexamples
In the case of the dangling else, Bison found an example that can be
parsed in two ways (therefore proving that the grammar is ambiguous).
When it cannot find such an example, it instead generates two examples
that are the same up until the dot:
$ bison foo.y
foo.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
foo.y: note: rerun with option '-Wcounterexamples' to generate conflict counterexamples
foo.y:4.4-7: warning: rule useless in parser due to conflicts [-Wother]
4 | a: expr
| ^~~~
$ bison -Wcex foo.y
foo.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
foo.y: warning: shift/reduce conflict on token ID [-Wcounterexamples]
First example: expr • ID ',' ID $end
Shift derivation
$accept
↳ s $end
↳ a ID
↳ expr
↳ expr • ID ','
Second example: expr • ID $end
Reduce derivation
$accept
↳ s $end
↳ a ID
↳ expr •
foo.y:4.4-7: warning: rule useless in parser due to conflicts [-Wother]
4 | a: expr
| ^~~~
In these cases, the parser usually doesn't have enough lookahead to
differentiate the two given examples.
**** Reports
Counterexamples are also included in the report when given
`--report=counterexamples`/`-rcex` (or `--report=all`), with more
technical details:
State 7
1 exp: "if" exp "then" exp • [$end, "then", "else"]
2 | "if" exp "then" exp • "else" exp
"else" shift, and go to state 8
"else" [reduce using rule 1 (exp)]
$default reduce using rule 1 (exp)
shift/reduce conflict on token "else":
1 exp: "if" exp "then" exp •
2 exp: "if" exp "then" exp • "else" exp
Example: "if" exp "then" "if" exp "then" exp • "else" exp
Shift derivation
exp
↳ "if" exp "then" exp
↳ "if" exp "then" exp • "else" exp
Example: "if" exp "then" "if" exp "then" exp • "else" exp
Reduce derivation
exp
↳ "if" exp "then" exp "else" exp
↳ "if" exp "then" exp •
*** File prefix mapping
Contributed by Joshua Watt.
Bison learned a new argument, `--file-prefix-map OLD=NEW`. Any file path
in the output (specifically `#line` directives and `#ifdef` header guards)
that begins with the prefix OLD will have it replaced with the prefix NEW,
similar to the `-ffile-prefix-map` in GCC. This option can be used to
make bison output reproducible.
** Changes
*** Diagnostics
When text styling is enabled and the terminal supports it, the warnings
now include hyperlinks to the documentation.
*** Relocatable installation
When installed to be relocatable (via `configure --enable-relocatable`),
bison will now also look for a relocated m4.
*** C++ file names
The `filename_type` %define variable was renamed `api.filename.type`.
Instead of
%define filename_type "symbol"
write
%define api.filename.type {symbol}
(Or let `bison --update` do it for you).
It now defaults to `const std::string` instead of `std::string`.
*** Deprecated %define variable names
The following variables have been renamed for consistency. Backward
compatibility is ensured, but upgrading is recommended.
filename_type -> api.filename.type
package -> api.package
*** Push parsers no longer clear their state when parsing is finished
Previously push-parsers cleared their state when parsing was finished (on
success and on failure). This made it impossible to check if there were
parse errors, since `yynerrs` was also reset. This can be especially
troublesome when used in autocompletion, since a parser with error
recovery would suggest (irrelevant) expected tokens even if there were
failure.
Now the parser state can be examined when parsing is finished. The parser
state is reset when starting a new parse.
** Documentation
*** Examples
The bistromathic demonstrates %param and how to quote sources in the error
messages:
> 123 456
1.5-7: syntax error: expected end of file or + or - or * or / or ^ before number
1 | 123 456
| ^~~
** Bug fixes
*** Include the generated header (yacc.c)
Historically, when --defines was used, bison generated a header and pasted
an exact copy of it into the generated parser implementation file. Since
Bison 3.4 it is possible to specify that the header should be `#include`d,
and how. For instance
%define api.header.include {"parse.h"}
or
%define api.header.include {<parser/parse.h>}
Now api.header.include defaults to `"header-basename"`, as was intended in
Bison 3.4, where `header-basename` is the basename of the generated
header. This is disabled when the generated header is `y.tab.h`, to
comply with Automake's ylwrap.
*** String aliases are faithfully propagated
Bison used to interpret user strings (i.e., decoding backslash escapes)
when reading them, and to escape them (i.e., issue non-printable
characters as backslash escapes, taking the locale into account) when
outputting them. As a consequence non-ASCII strings (say in UTF-8) ended
up "ciphered" as sequences of backslash escapes. This happened not only
in the generated sources (where the compiler will reinterpret them), but
also in all the generated reports (text, xml, html, dot, etc.). Reports
were therefore not readable when string aliases were not pure ASCII.
Worse yet: the output depended on the user's locale.
Now Bison faithfully treats the string aliases exactly the way the user
spelled them. This fixes all the aforementioned problems. However, now,
string aliases semantically equivalent but syntactically different (e.g.,
"A", "\x41", "\101") are considered to be different.
*** Crash when generating IELR
An old, well hidden, bug in the generation of IELR parsers was fixed.
* Noteworthy changes in release 3.6.4 (2020-06-15) [stable]
** Bug fixes
In glr.cc some internal macros leaked in the user's code, and could damage
access to the token kinds.
* Noteworthy changes in release 3.6.3 (2020-06-03) [stable]
** Bug fixes
Incorrect comments in the generated parsers.
Warnings in push parsers (yacc.c).
Incorrect display of gotos in LAC traces (lalr1.cc).
* Noteworthy changes in release 3.6.2 (2020-05-17) [stable]
** Bug fixes
Some tests were fixed.
When token aliases contain comment delimiters:
%token FOO "/* foo */"
bison used to emit "nested" comments, which is invalid C.
* Noteworthy changes in release 3.6.1 (2020-05-10) [stable]
** Bug fixes
Restored ANSI-C compliance in yacc.c.
GNU readline portability issues.
In C++, yy::parser::symbol_name is now a public member, as was intended.
** New features
In C++, yy::parser::symbol_type now has a public name() member function.
* Noteworthy changes in release 3.6 (2020-05-08) [stable]
** Backward incompatible changes
TL;DR: replace "#define YYERROR_VERBOSE 1" by "%define parse.error verbose".
The YYERROR_VERBOSE macro is no longer supported; the parsers that still
depend on it will now produce Yacc-like error messages (just "syntax
error"). It was superseded by the "%error-verbose" directive in Bison
1.875 (2003-01-01). Bison 2.6 (2012-07-19) clearly announced that support
for YYERROR_VERBOSE would be removed. Note that since Bison 3.0
(2013-07-25), "%error-verbose" is deprecated in favor of "%define
parse.error verbose".
** Deprecated features
The YYPRINT macro, which works only with yacc.c and only for tokens, was
obsoleted long ago by %printer, introduced in Bison 1.50 (November 2002).
It is deprecated and its support will be removed eventually.
** New features
*** Improved syntax error messages
Two new values for the %define parse.error variable offer more control to
the user. Available in all the skeletons (C, C++, Java).
**** %define parse.error detailed
The behavior of "%define parse.error detailed" is closely resembling that
of "%define parse.error verbose" with a few exceptions. First, it is safe
to use non-ASCII characters in token aliases (with 'verbose', the result
depends on the locale with which bison was run). Second, a yysymbol_name
function is exposed to the user, instead of the yytnamerr function and the
yytname table. Third, token internationalization is supported (see
below).
**** %define parse.error custom
With this directive, the user forges and emits the syntax error message
herself by defining the yyreport_syntax_error function. A new type,
yypcontext_t, captures the circumstances of the error, and provides the
user with functions to get details, such as yypcontext_expected_tokens to
get the list of expected token kinds.
A possible implementation of yyreport_syntax_error is:
int
yyreport_syntax_error (const yypcontext_t *ctx)
{
int res = 0;
YY_LOCATION_PRINT (stderr, *yypcontext_location (ctx));
fprintf (stderr, ": syntax error");
// Report the tokens expected at this point.
{
enum { TOKENMAX = 10 };
yysymbol_kind_t expected[TOKENMAX];
int n = yypcontext_expected_tokens (ctx, expected, TOKENMAX);
if (n < 0)
// Forward errors to yyparse.
res = n;
else
for (int i = 0; i < n; ++i)
fprintf (stderr, "%s %s",
i == 0 ? ": expected" : " or", yysymbol_name (expected[i]));
}
// Report the unexpected token.
{
yysymbol_kind_t lookahead = yypcontext_token (ctx);
if (lookahead != YYSYMBOL_YYEMPTY)
fprintf (stderr, " before %s", yysymbol_name (lookahead));
}
fprintf (stderr, "\n");
return res;
}
**** Token aliases internationalization
When the %define variable parse.error is set to `custom` or `detailed`,
one may specify which token aliases are to be translated using _(). For
instance
%token
PLUS "+"
MINUS "-"
<double>
NUM _("number")
<symrec*>
FUN _("function")
VAR _("variable")
In that case the user must define _() and N_(), and yysymbol_name returns
the translated symbol (i.e., it returns '_("variable")' rather that
'"variable"'). In Java, the user must provide an i18n() function.
*** List of expected tokens (yacc.c)
Push parsers may invoke yypstate_expected_tokens at any point during
parsing (including even before submitting the first token) to get the list
of possible tokens. This feature can be used to propose autocompletion
(see below the "bistromathic" example).
It makes little sense to use this feature without enabling LAC (lookahead
correction).
*** Returning the error token
When the scanner returns an invalid token or the undefined token
(YYUNDEF), the parser generates an error message and enters error
recovery. Because of that error message, most scanners that find lexical
errors generate an error message, and then ignore the invalid input
without entering the error-recovery.
The scanners may now return YYerror, the error token, to enter the
error-recovery mode without triggering an additional error message. See
the bistromathic for an example.
*** Deep overhaul of the symbol and token kinds
To avoid the confusion with types in programming languages, we now refer
to token and symbol "kinds" instead of token and symbol "types". The
documentation and error messages have been revised.
All the skeletons have been updated to use dedicated enum types rather
than integral types. Special symbols are now regular citizens, instead of
being declared in ad hoc ways.
**** Token kinds
The "token kind" is what is returned by the scanner, e.g., PLUS, NUMBER,
LPAREN, etc. While backward compatibility is of course ensured, users are
nonetheless invited to replace their uses of "enum yytokentype" by
"yytoken_kind_t".
This type now also includes tokens that were previously hidden: YYEOF (end
of input), YYUNDEF (undefined token), and YYerror (error token). They
now have string aliases, internationalized when internationalization is
enabled. Therefore, by default, error messages now refer to "end of file"
(internationalized) rather than the cryptic "$end", or to "invalid token"
rather than "$undefined".
Therefore in most cases it is now useless to define the end-of-line token
as follows:
%token T_EOF 0 "end of file"
Rather simply use "YYEOF" in your scanner.
**** Symbol kinds
The "symbol kinds" is what the parser actually uses. (Unless the
api.token.raw %define variable is used, the symbol kind of a terminal
differs from the corresponding token kind.)
They are now exposed as a enum, "yysymbol_kind_t".
This allows users to tailor the error messages the way they want, or to
process some symbols in a specific way in autocompletion (see the
bistromathic example below).
*** Modernize display of explanatory statements in diagnostics
Since Bison 2.7, output was indented four spaces for explanatory
statements. For example:
input.y:2.7-13: error: %type redeclaration for exp
input.y:1.7-11: previous declaration
Since the introduction of caret-diagnostics, it became less clear. This
indentation has been removed and submessages are displayed similarly as in
GCC:
input.y:2.7-13: error: %type redeclaration for exp
2 | %type <float> exp
| ^~~~~~~
input.y:1.7-11: note: previous declaration
1 | %type <int> exp
| ^~~~~
Contributed by Victor Morales Cayuela.
*** C++
The token and symbol kinds are yy::parser::token_kind_type and
yy::parser::symbol_kind_type.
The symbol_type::kind() member function allows to get the kind of a
symbol. This can be used to write unit tests for scanners, e.g.,
yy::parser::symbol_type t = make_NUMBER ("123");
assert (t.kind () == yy::parser::symbol_kind::S_NUMBER);
assert (t.value.as<int> () == 123);
** Documentation
*** User Manual
In order to avoid ambiguities with "type" as in "typing", we now refer to
the "token kind" (e.g., `PLUS`, `NUMBER`, etc.) rather than the "token
type". We now also refer to the "symbol type" (e.g., `PLUS`, `expr`,
etc.).
*** Examples
There are now examples/java: a very simple calculator, and a more complete
one (push-parser, location tracking, and debug traces).
The lexcalc example (a simple example in C based on Flex and Bison) now
also demonstrates location tracking.
A new C example, bistromathic, is a fully featured interactive calculator
using many Bison features: pure interface, push parser, autocompletion
based on the current parser state (using yypstate_expected_tokens),
location tracking, internationalized custom error messages, lookahead
correction, rich debug traces, etc.
It shows how to depend on the symbol kinds to tailor autocompletion. For
instance it recognizes the symbol kind "VARIABLE" to propose
autocompletion on the existing variables, rather than of the word
"variable".
* Noteworthy changes in release 3.5.4 (2020-04-05) [stable]
** WARNING: Future backward-incompatibilities!
TL;DR: replace "#define YYERROR_VERBOSE 1" by "%define parse.error verbose".
Bison 3.6 will no longer support the YYERROR_VERBOSE macro; the parsers
that still depend on it will produce Yacc-like error messages (just
"syntax error"). It was superseded by the "%error-verbose" directive in
Bison 1.875 (2003-01-01). Bison 2.6 (2012-07-19) clearly announced that
support for YYERROR_VERBOSE would be removed. Note that since Bison 3.0
(2013-07-25), "%error-verbose" is deprecated in favor of "%define
parse.error verbose".
** Bug fixes
Fix portability issues of the package itself on old compilers.
Fix api.token.raw support in Java.
* Noteworthy changes in release 3.5.3 (2020-03-08) [stable]
** Bug fixes
Error messages could quote lines containing zero-width characters (such as
\005) with incorrect styling. Fixes for similar issues with unexpectedly
short lines (e.g., the file was changed between parsing and diagnosing).
Several unlikely crashes found by fuzzing have been fixed.
* Noteworthy changes in release 3.5.2 (2020-02-13) [stable]
** Bug fixes
Portability issues and minor cosmetic issues.
The lalr1.cc skeleton properly rejects unsupported values for parse.lac
(as yacc.c does).
* Noteworthy changes in release 3.5.1 (2020-01-19) [stable]
** Bug fixes
Portability fixes.
Fix compiler warnings.
* Noteworthy changes in release 3.5 (2019-12-11) [stable]
** Backward incompatible changes
Lone carriage-return characters (aka \r or ^M) in the grammar files are no
longer treated as end-of-lines. This changes the diagnostics, and in
particular their locations.
In C++, line numbers and columns are now represented as 'int' not
'unsigned', so that integer overflow on positions is easily checkable via
'gcc -fsanitize=undefined' and the like. This affects the API for
positions. The default position and location classes now expose
'counter_type' (int), used to define line and column numbers.
** Deprecated features
The YYPRINT macro, which works only with yacc.c and only for tokens, was
obsoleted long ago by %printer, introduced in Bison 1.50 (November 2002).
It is deprecated and its support will be removed eventually.
** New features
*** Lookahead correction in C++
Contributed by Adrian Vogelsgesang.
The C++ deterministic skeleton (lalr1.cc) now supports LAC, via the
%define variable parse.lac.
*** Variable api.token.raw: Optimized token numbers (all skeletons)
In the generated parsers, tokens have two numbers: the "external" token
number as returned by yylex (which starts at 257), and the "internal"
symbol number (which starts at 3). Each time yylex is called, a table
lookup maps the external token number to the internal symbol number.
When the %define variable api.token.raw is set, tokens are assigned their
internal number, which saves one table lookup per token, and also saves
the generation of the mapping table.
The gain is typically moderate, but in extreme cases (very simple user
actions), a 10% improvement can be observed.
*** Generated parsers use better types for states
Stacks now use the best integral type for state numbers, instead of always
using 15 bits. As a result "small" parsers now have a smaller memory
footprint (they use 8 bits), and there is support for large automata (16
bits), and extra large (using int, i.e., typically 31 bits).
*** Generated parsers prefer signed integer types
Bison skeletons now prefer signed to unsigned integer types when either
will do, as the signed types are less error-prone and allow for better
checking with 'gcc -fsanitize=undefined'. Also, the types chosen are now
portable to unusual machines where char, short and int are all the same
width. On non-GNU platforms this may entail including <limits.h> and (if
available) <stdint.h> to define integer types and constants.
*** A skeleton for the D programming language
For the last few releases, Bison has shipped a stealth experimental
skeleton: lalr1.d. It was first contributed by Oliver Mangold, based on
Paolo Bonzini's lalr1.java, and was cleaned and improved thanks to
H. S. Teoh.
However, because nobody has committed to improving, testing, and
documenting this skeleton, it is not clear that it will be supported in
the future.
The lalr1.d skeleton *is functional*, and works well, as demonstrated in
examples/d/calc.d. Please try it, enjoy it, and... commit to support it.
*** Debug traces in Java
The Java backend no longer emits code and data for parser tracing if the
%define variable parse.trace is not defined.
** Diagnostics
*** New diagnostic: -Wdangling-alias
String literals, which allow for better error messages, are (too)
liberally accepted by Bison, which might result in silent errors. For
instance
%type <exVal> cond "condition"
does not define "condition" as a string alias to 'cond' (nonterminal
symbols do not have string aliases). It is rather equivalent to
%nterm <exVal> cond
%token <exVal> "condition"
i.e., it gives the type 'exVal' to the "condition" token, which was
clearly not the intention.
Also, because string aliases need not be defined, typos such as "baz"
instead of "bar" will be not reported.
The option -Wdangling-alias catches these situations. On
%token BAR "bar"
%type <ival> foo "foo"
%%
foo: "baz" {}
bison -Wdangling-alias reports
warning: string literal not attached to a symbol
| %type <ival> foo "foo"
| ^~~~~
warning: string literal not attached to a symbol
| foo: "baz" {}
| ^~~~~
The -Wall option does not (yet?) include -Wdangling-alias.
*** Better POSIX Yacc compatibility diagnostics
POSIX Yacc restricts %type to nonterminals. This is now diagnosed by
-Wyacc.
%token TOKEN1
%type <ival> TOKEN1 TOKEN2 't'
%token TOKEN2
%%
expr:
gives with -Wyacc
input.y:2.15-20: warning: POSIX yacc reserves %type to nonterminals [-Wyacc]
2 | %type <ival> TOKEN1 TOKEN2 't'
| ^~~~~~
input.y:2.29-31: warning: POSIX yacc reserves %type to nonterminals [-Wyacc]
2 | %type <ival> TOKEN1 TOKEN2 't'
| ^~~
input.y:2.22-27: warning: POSIX yacc reserves %type to nonterminals [-Wyacc]
2 | %type <ival> TOKEN1 TOKEN2 't'
| ^~~~~~
*** Diagnostics with insertion
The diagnostics now display the suggestion below the underlined source.
Replacement for undeclared symbols are now also suggested.
$ cat /tmp/foo.y
%%
list: lis '.' |
$ bison -Wall foo.y
foo.y:2.7-9: error: symbol 'lis' is used, but is not defined as a token and has no rules; did you mean 'list'?
2 | list: lis '.' |
| ^~~
| list
foo.y:2.16: warning: empty rule without %empty [-Wempty-rule]
2 | list: lis '.' |
| ^
| %empty
foo.y: warning: fix-its can be applied. Rerun with option '--update'. [-Wother]
*** Diagnostics about long lines
Quoted sources may now be truncated to fit the screen. For instance, on a
30-column wide terminal:
$ cat foo.y
%token FOO FOO FOO
%%
exp: FOO
$ bison foo.y
foo.y:1.34-36: warning: symbol FOO redeclared [-Wother]
1 | … FOO …
| ^~~
foo.y:1.8-10: previous declaration
1 | %token FOO …
| ^~~
foo.y:1.62-64: warning: symbol FOO redeclared [-Wother]
1 | … FOO
| ^~~
foo.y:1.8-10: previous declaration
1 | %token FOO …
| ^~~
** Changes
*** Debugging glr.c and glr.cc
The glr.c skeleton always had asserts to check its own behavior (not the
user's). These assertions are now under the control of the parse.assert
%define variable (disabled by default).
*** Clean up
Several new compiler warnings in the generated output have been avoided.
Some unused features are no longer emitted. Cleaner generated code in
general.
** Bug Fixes
Portability issues in the test suite.
In theory, parsers using %nonassoc could crash when reporting verbose
error messages. This unlikely bug has been fixed.
In Java, %define api.prefix was ignored. It now behaves as expected.
pkglint --only "https instead of http" -r -F
With manual adjustments afterwards since pkglint 19.4.4 fixed a few
indentations in unrelated lines.
This mainly affects projects hosted at SourceForce, as well as
freedesktop.org, CTAN and GNU.
upstream changes:
-----------------
GNU Bison NEWS
* Noteworthy changes in release 3.4.2 (2019-09-12) [stable]
** Bug fixes
In some cases, when warnings are disabled, bison could emit tons of white
spaces as diagnostics.
When running out of memory, bison could crash (found by fuzzing).
When defining twice the EOF token, bison would crash.
New warnings from recent compilers have been addressed in the generated
parsers (yacc.c, glr.c, glr.cc).
When lone carriage-return characters appeared in the input file,
diagnostics could hang forever.
* Noteworthy changes in release 3.4.1 (2019-05-22) [stable]
** Bug fixes
Portability fixes.
* Noteworthy changes in release 3.4 (2019-05-19) [stable]
** Deprecated features
The %pure-parser directive is deprecated in favor of '%define api.pure'
since Bison 2.3b (2008-05-27), but no warning was issued; there is one
now. Note that since Bison 2.7 you are strongly encouraged to use
'%define api.pure full' instead of '%define api.pure'.
** New features
*** Colored diagnostics
As an experimental feature, diagnostics are now colored, controlled by the
new options --color and --style.
To use them, install the libtextstyle library before configuring Bison.
It is available from
https://alpha.gnu.org/gnu/gettext/
for instance
https://alpha.gnu.org/gnu/gettext/libtextstyle-0.8.tar.gz
The option --color supports the following arguments:
- always, yes: Enable colors.
- never, no: Disable colors.
- auto, tty (default): Enable colors if the output device is a tty.
To customize the styles, create a CSS file similar to
/* bison-bw.css */
.warning { }
.error { font-weight: 800; text-decoration: underline; }
.note { }
then invoke bison with --style=bison-bw.css, or set the BISON_STYLE
environment variable to "bison-bw.css".
*** Disabling output
When given -fsyntax-only, the diagnostics are reported, but no output is
generated.
The name of this option is somewhat misleading as bison does more than
just checking the syntax: every stage is run (including checking for
conflicts for instance), except the generation of the output files.
*** Include the generated header (yacc.c)
Before, when --defines is used, bison generated a header, and pasted an
exact copy of it into the generated parser implementation file. If the
header name is not "y.tab.h", it is now #included instead of being
duplicated.
To use an '#include' even if the header name is "y.tab.h" (which is what
happens with --yacc, or when using the Autotools' ylwrap), define
api.header.include to the exact argument to pass to #include. For
instance:
%define api.header.include {"parse.h"}
or
%define api.header.include {<parser/parse.h>}
*** api.location.type is now supported in C (yacc.c, glr.c)
The %define variable api.location.type defines the name of the type to use
for locations. When defined, Bison no longer defines YYLTYPE.
This can be used in programs with several parsers to factor their
definition of locations: let one of them generate them, and the others
just use them.
** Changes
*** Graphviz output
In conformance with the recommendations of the Graphviz team, if %require
"3.4" (or better) is specified, the option --graph generates a *.gv file
by default, instead of *.dot.
*** Diagnostics overhaul
Column numbers were wrong with multibyte characters, which would also
result in skewed diagnostics with carets. Beside, because we were
indenting the quoted source with a single space, lines with tab characters
were incorrectly underlined.
To address these issues, and to be clearer, Bison now issues diagnostics
as GCC9 does. For instance it used to display (there's a tab before the
opening brace):
foo.y:3.37-38: error: $2 of ‘expr’ has no declared type
expr: expr '+' "number" { $$ = $1 + $2; }
^~
It now reports
foo.y:3.37-38: error: $2 of ‘expr’ has no declared type
3 | expr: expr '+' "number" { $$ = $1 + $2; }
| ^~
Other constructs now also have better locations, resulting in more precise
diagnostics.
*** Fix-it hints for %empty
Running Bison with -Wempty-rules and --update will remove incorrect %empty
annotations, and add the missing ones.
*** Generated reports
The format of the reports (parse.output) was improved for readability.
*** Better support for --no-line.
When --no-line is used, the generated files are now cleaner: no lines are
generated instead of empty lines. Together with using api.header.include,
that should help people saving the generated files into version control
systems get smaller diffs.
** Documentation
A new example in C shows an simple infix calculator with a hand-written
scanner (examples/c/calc).
A new example in C shows a reentrant parser (capable of recursive calls)
built with Flex and Bison (examples/c/reccalc).
There is a new section about the history of Yaccs and Bison.
** Bug fixes
A few obscure bugs were fixed, including the second oldest (known) bug in
Bison: it was there when Bison was entered in the RCS version control
system, in December 1987. See the NEWS of Bison 3.3 for the previous
oldest bug.
* Noteworthy changes in release 3.3.2 (2019-02-03) [stable]
** Bug fixes
Bison 3.3 failed to generate parsers for grammars with unused nonterminal
symbols.
* Noteworthy changes in release 3.3.1 (2019-01-27) [stable]
** Changes
The option -y/--yacc used to imply -Werror=yacc, which turns uses of Bison
extensions into errors. It now makes them simple warnings (-Wyacc).
* Noteworthy changes in release 3.3 (2019-01-26) [stable]
A new mailing list was created, Bison Announce. It is low traffic, and is
only about announcing new releases and important messages (e.g., polls
about major decisions to make).
https://lists.gnu.org/mailman/listinfo/bison-announce
** Backward incompatible changes
Support for DJGPP, which has been unmaintained and untested for years, is
removed.
** Deprecated features
A new feature, --update (see below) helps adjusting existing grammars to
deprecations.
*** Deprecated directives
The %error-verbose directive is deprecated in favor of '%define
parse.error verbose' since Bison 3.0, but no warning was issued.
The '%name-prefix "xx"' directive is deprecated in favor of '%define
api.prefix {xx}' since Bison 3.0, but no warning was issued. These
directives are slightly different, you might need to adjust your code.
%name-prefix renames only symbols with external linkage, while api.prefix
also renames types and macros, including YYDEBUG, YYTOKENTYPE,
yytokentype, YYSTYPE, YYLTYPE, etc.
Users of Flex that move from '%name-prefix "xx"' to '%define api.prefix
{xx}' will typically have to update YY_DECL from
#define YY_DECL int xxlex (YYSTYPE *yylval, YYLTYPE *yylloc)
to
#define YY_DECL int xxlex (XXSTYPE *yylval, XXLTYPE *yylloc)
*** Deprecated %define variable names
The following variables, mostly related to parsers in Java, have been
renamed for consistency. Backward compatibility is ensured, but upgrading
is recommended.
abstract -> api.parser.abstract
annotations -> api.parser.annotations
extends -> api.parser.extends
final -> api.parser.final
implements -> api.parser.implements
parser_class_name -> api.parser.class
public -> api.parser.public
strictfp -> api.parser.strictfp
** New features
*** Generation of fix-its for IDEs/Editors
When given the new option -ffixit (aka -fdiagnostics-parseable-fixits),
bison now generates machine readable editing instructions to fix some
issues. Currently, this is mostly limited to updating deprecated
directives and removing duplicates. For instance:
$ cat foo.y
%error-verbose
%define parser_class_name "Parser"
%define api.parser.class "Parser"
%%
exp:;
See the "fix-it:" lines below:
$ bison -ffixit foo.y
foo.y:1.1-14: warning: deprecated directive, use '%define parse.error verbose' [-Wdeprecated]
%error-verbose
^~~~~~~~~~~~~~
fix-it:"foo.y":{1:1-1:15}:"%define parse.error verbose"
foo.y:2.1-34: warning: deprecated directive, use '%define api.parser.class {Parser}' [-Wdeprecated]
%define parser_class_name "Parser"
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
fix-it:"foo.y":{2:1-2:35}:"%define api.parser.class {Parser}"
foo.y:3.1-33: error: %define variable 'api.parser.class' redefined
%define api.parser.class "Parser"
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.y:2.1-34: previous definition
%define parser_class_name "Parser"
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
fix-it:"foo.y":{3:1-3:34}:""
foo.y: warning: fix-its can be applied. Rerun with option '--update'. [-Wother]
This uses the same output format as GCC and Clang.
*** Updating grammar files
Fixes can be applied on the fly. The previous example ends with the
suggestion to re-run bison with the option -u/--update, which results in a
cleaner grammar file.
$ bison --update foo.y
[...]
bison: file 'foo.y' was updated (backup: 'foo.y~')
$ cat foo.y
%define parse.error verbose
%define api.parser.class {Parser}
%%
exp:;
*** Bison is now relocatable
If you pass '--enable-relocatable' to 'configure', Bison is relocatable.
A relocatable program can be moved or copied to a different location on
the file system. It can also be used through mount points for network
sharing. It is possible to make symbolic links to the installed and moved
programs, and invoke them through the symbolic link.
*** %expect and %expect-rr modifiers on individual rules
One can now document (and check) which rules participate in shift/reduce
and reduce/reduce conflicts. This is particularly important GLR parsers,
where conflicts are a normal occurrence. For example,
%glr-parser
%expect 1
%%
...
argument_list:
arguments %expect 1
| arguments ','
| %empty
;
arguments:
expression
| argument_list ',' expression
;
...
Looking at the output from -v, one can see that the shift-reduce conflict
here is due to the fact that the parser does not know whether to reduce
arguments to argument_list until it sees the token _after_ the following
','. By marking the rule with %expect 1 (because there is a conflict in
one state), we document the source of the 1 overall shift-reduce conflict.
In GLR parsers, we can use %expect-rr in a rule for reduce/reduce
conflicts. In this case, we mark each of the conflicting rules. For
example,
%glr-parser
%expect-rr 1
%%
stmt:
target_list '=' expr ';'
| expr_list ';'
;
target_list:
target
| target ',' target_list
;
target:
ID %expect-rr 1
;
expr_list:
expr
| expr ',' expr_list
;
expr:
ID %expect-rr 1
| ...
;
In a statement such as
x, y = 3, 4;
the parser must reduce x to a target or an expr, but does not know which
until it sees the '='. So we notate the two possible reductions to
indicate that each conflicts in one rule.
This feature needs user feedback, and might evolve in the future.
*** C++: Actual token constructors
When variants and token constructors are enabled, in addition to the
type-safe named token constructors (make_ID, make_INT, etc.), we now
generate genuine constructors for symbol_type.
For instance with these declarations
%token ':'
<std::string> ID
<int> INT;
you may use these constructors:
symbol_type (int token, const std::string&);
symbol_type (int token, const int&);
symbol_type (int token);
Correct matching between token types and value types is checked via
'assert'; for instance, 'symbol_type (ID, 42)' would abort. Named
constructors are preferable, as they offer better type safety (for
instance 'make_ID (42)' would not even compile), but symbol_type
constructors may help when token types are discovered at run-time, e.g.,
[a-z]+ {
if (auto i = lookup_keyword (yytext))
return yy::parser::symbol_type (i);
else
return yy::parser::make_ID (yytext);
}
*** C++: Variadic emplace
If your application requires C++11 and you don't use symbol constructors,
you may now use a variadic emplace for semantic values:
%define api.value.type variant
%token <std::pair<int, int>> PAIR
in your scanner:
int yylex (parser::semantic_type *lvalp)
{
lvalp->emplace <std::pair<int, int>> (1, 2);
return parser::token::PAIR;
}
*** C++: Syntax error exceptions in GLR
The glr.cc skeleton now supports syntax_error exceptions thrown from user
actions, or from the scanner.
*** More POSIX Yacc compatibility warnings
More Bison specific directives are now reported with -y or -Wyacc. This
change was ready since the release of Bison 3.0 in September 2015. It was
delayed because Autoconf used to define YACC as `bison -y`, which resulted
in numerous warnings for Bison users that use the GNU Build System.
If you still experience that problem, either redefine YACC as `bison -o
y.tab.c`, or pass -Wno-yacc to Bison.
*** The tables yyrhs and yyphrs are back
Because no Bison skeleton uses them, these tables were removed (no longer
passed to the skeletons, not even computed) in 2008. However, some users
have expressed interest in being able to use them in their own skeletons.
** Bug fixes
*** Incorrect number of reduce-reduce conflicts
On a grammar such as
exp: "num" | "num" | "num"
bison used to report a single RR conflict, instead of two. This is now
fixed. This was the oldest (known) bug in Bison: it was there when Bison
was entered in the RCS version control system, in December 1987.
Some grammar files might have to adjust their %expect-rr.
*** Parser directives that were not careful enough
Passing invalid arguments to %nterm, for instance character literals, used
to result in unclear error messages.
** Documentation
The examples/ directory (installed in .../share/doc/bison/examples) has
been restructured per language for clarity. The examples come with a
README and a Makefile. Not only can they be used to toy with Bison, they
can also be starting points for your own grammars.
There is now a Java example, and a simple example in C based on Flex and
Bison (examples/c/lexcalc/).
** Changes
*** Parsers in C++
They now use noexcept and constexpr. Please, report missing annotations.
*** Symbol Declarations
The syntax of the variation directives to declare symbols was overhauled
for more consistency, and also better POSIX Yacc compliance (which, for
instance, allows "%type" without actually providing a type). The %nterm
directive, supported by Bison since its inception, is now documented and
officially supported.
The syntax is now as follows:
%token TAG? ( ID NUMBER? STRING? )+ ( TAG ( ID NUMBER? STRING? )+ )*
%left TAG? ( ID NUMBER? )+ ( TAG ( ID NUMBER? )+ )*
%type TAG? ( ID | CHAR | STRING )+ ( TAG ( ID | CHAR | STRING )+ )*
%nterm TAG? ID+ ( TAG ID+ )*
where TAG denotes a type tag such as ‘<ival>’, ID denotes an identifier
such as ‘NUM’, NUMBER a decimal or hexadecimal integer such as ‘300’ or
‘0x12d’, CHAR a character literal such as ‘'+'’, and STRING a string
literal such as ‘"number"’. The post-fix quantifiers are ‘?’ (zero or
one), ‘*’ (zero or more) and ‘+’ (one or more).
* Noteworthy changes in release 3.2.4 (2018-12-24) [stable]
** Bug fixes
Fix the move constructor of symbol_type.
Always provide a copy constructor for symbol_type, even in modern C++.
* Noteworthy changes in release 3.2.3 (2018-12-18) [stable]
** Bug fixes
Properly support token constructors in C++ with types that include commas
(e.g., std::pair<int, int>). A regression introduced in Bison 3.2.
* Noteworthy changes in release 3.2.2 (2018-11-21) [stable]
** Bug fixes
C++ portability issues.
* Noteworthy changes in release 3.2.1 (2018-11-09) [stable]
** Bug fixes
Several portability issues have been fixed in the build system, in the
test suite, and in the generated parsers in C++.
* Noteworthy changes in release 3.2 (2018-10-29) [stable]
** Backward incompatible changes
Support for DJGPP, which have been unmaintained and untested for years, is
obsolete. Unless there is activity to revive it, it will be removed.
** Changes
%printers should use yyo rather than yyoutput to denote the output stream.
Variant-based symbols in C++ should use emplace() rather than build().
In C++ parsers, parser::operator() is now a synonym for the parser::parse.
** Documentation
A new section, "A Simple C++ Example", is a tutorial for parsers in C++.
A comment in the generated code now emphasizes that users should not
depend upon non-documented implementation details, such as macros starting
with YY_.
** New features
*** C++: Support for move semantics (lalr1.cc)
The lalr1.cc skeleton now fully supports C++ move semantics, while
maintaining compatibility with C++98. You may now store move-only types
when using Bison's variants. For instance:
%code {
#include <memory>
#include <vector>
}
%skeleton "lalr1.cc"
%define api.value.type variant
%%
%token <int> INT "int";
%type <std::unique_ptr<int>> int;
%type <std::vector<std::unique_ptr<int>>> list;
list:
%empty {}
| list int { $$ = std::move($1); $$.emplace_back(std::move($2)); }
int: "int" { $$ = std::make_unique<int>($1); }
*** C++: Implicit move of right-hand side values (lalr1.cc)
In modern C++ (C++11 and later), you should always use 'std::move' with
the values of the right-hand side symbols ($1, $2, etc.), as they will be
popped from the stack anyway. Using 'std::move' is mandatory for
move-only types such as unique_ptr, and it provides a significant speedup
for large types such as std::string, or std::vector, etc.
If '%define api.value.automove' is set, every occurrence '$n' is replaced
by 'std::move ($n)'. The second rule in the previous grammar can be
simplified to:
list: list int { $$ = $1; $$.emplace_back($2); }
With automove enabled, the semantic values are no longer lvalues, so do
not use the swap idiom:
list: list int { std::swap($$, $1); $$.emplace_back($2); }
This idiom is anyway obsolete: it is preferable to move than to swap.
A warning is issued when automove is enabled, and a value is used several
times.
input.yy:16.31-32: warning: multiple occurrences of $2 with api.value.automove enabled [-Wother]
exp: "twice" exp { $$ = $2 + $2; }
^^
Enabling api.value.automove does not require support for modern C++. The
generated code is valid C++98/03, but will use copies instead of moves.
The new examples/c++/variant-11.yy shows these features in action.
*** C++: The implicit default semantic action is always run
When variants are enabled, the default action was not run, so
exp: "number"
was equivalent to
exp: "number" {}
It now behaves like in all the other cases, as
exp: "number" { $$ = $1; }
possibly using std::move if automove is enabled.
We do not expect backward compatibility issues. However, beware of
forward compatibility issues: if you rely on default actions with
variants, be sure to '%require "3.2"' to avoid older versions of Bison to
generate incorrect parsers.
*** C++: Renaming location.hh
When both %defines and %locations are enabled, Bison generates a
location.hh file. If you don't use locations outside of the parser, you
may avoid its creation with:
%define api.location.file none
However this file is useful if, for instance, your parser builds an AST
decorated with locations: you may use Bison's location independently of
Bison's parser. You can now give it another name, for instance:
%define api.location.file "my-location.hh"
This name can have directory components, and even be absolute. The name
under which the location file is included is controlled by
api.location.include.
This way it is possible to have several parsers share the same location
file.
For instance, in src/foo/parser.hh, generate the include/ast/loc.hh file:
%locations
%define api.namespace {foo}
%define api.location.file "include/ast/loc.hh"
%define api.location.include {<ast/loc.hh>}
and use it in src/bar/parser.hh:
%locations
%define api.namespace {bar}
%code requires {#include <ast/loc.hh>}
%define api.location.type {bar::location}
Absolute file names are supported, so in your Makefile, passing the flag
-Dapi.location.file='"$(top_srcdir)/include/ast/location.hh"' to bison is
safe.
*** C++: stack.hh and position.hh are deprecated
When asked to generate a header file (%defines), the lalr1.cc skeleton
generates a stack.hh file. This file had no interest for users; it is now
made useless: its content is included in the parser definition. It is
still generated for backward compatibility.
When in addition to %defines, location support is requested (%locations),
the file position.hh is also generated. It is now also useless: its
content is now included in location.hh.
These files are no longer generated when your grammar file requires at
least Bison 3.2 (%require "3.2").
** Bug fixes
Portability issues on MinGW and VS2015.
Portability issues in the test suite.
Portability/warning issues with Flex.
* Noteworthy changes in release 3.1 (2018-08-27) [stable]
** Backward incompatible changes
Compiling Bison now requires a C99 compiler---as announced during the
release of Bison 3.0, five years ago. Generated parsers do not require a
C99 compiler.
Support for DJGPP, which have been unmaintained and untested for years, is
obsolete. Unless there is activity to revive it, the next release of Bison
will have it removed.
** New features
*** Typed midrule actions
Because their type is unknown to Bison, the values of midrule actions are
not treated like the others: they don't have %printer and %destructor
support. It also prevents C++ (Bison) variants to handle them properly.
Typed midrule actions address these issues. Instead of:
exp: { $<ival>$ = 1; } { $<ival>$ = 2; } { $$ = $<ival>1 + $<ival>2; }
write:
exp: <ival>{ $$ = 1; } <ival>{ $$ = 2; } { $$ = $1 + $2; }
*** Reports include the type of the symbols
The sections about terminal and nonterminal symbols of the '*.output' file
now specify their declared type. For instance, for:
%token <ival> NUM
the report now shows '<ival>':
Terminals, with rules where they appear
NUM <ival> (258) 5
*** Diagnostics about useless rules
In the following grammar, the 'exp' nonterminal is trivially useless. So,
of course, its rules are useless too.
%%
input: '0' | exp
exp: exp '+' exp | exp '-' exp | '(' exp ')'
Previously all the useless rules were reported, including those whose
left-hand side is the 'exp' nonterminal:
warning: 1 nonterminal useless in grammar [-Wother]
warning: 4 rules useless in grammar [-Wother]
2.14-16: warning: nonterminal useless in grammar: exp [-Wother]
input: '0' | exp
^^^
2.14-16: warning: rule useless in grammar [-Wother]
input: '0' | exp
^^^
3.6-16: warning: rule useless in grammar [-Wother]
exp: exp '+' exp | exp '-' exp | '(' exp ')'
^^^^^^^^^^^
3.20-30: warning: rule useless in grammar [-Wother]
exp: exp '+' exp | exp '-' exp | '(' exp ')'
^^^^^^^^^^^
3.34-44: warning: rule useless in grammar [-Wother]
exp: exp '+' exp | exp '-' exp | '(' exp ')'
^^^^^^^^^^^
Now, rules whose left-hand side symbol is useless are no longer reported
as useless. The locations of the errors have also been adjusted to point
to the first use of the nonterminal as a left-hand side of a rule:
warning: 1 nonterminal useless in grammar [-Wother]
warning: 4 rules useless in grammar [-Wother]
3.1-3: warning: nonterminal useless in grammar: exp [-Wother]
exp: exp '+' exp | exp '-' exp | '(' exp ')'
^^^
2.14-16: warning: rule useless in grammar [-Wother]
input: '0' | exp
^^^
*** C++: Generated parsers can be compiled with -fno-exceptions (lalr1.cc)
When compiled with exceptions disabled, the generated parsers no longer
uses try/catch clauses.
Currently only GCC and Clang are supported.
** Documentation
*** A demonstration of variants
A new example was added (installed in .../share/doc/bison/examples),
'variant.yy', which shows how to use (Bison) variants in C++.
The other examples were made nicer to read.
*** Some features are no longer 'experimental'
The following features, mature enough, are no longer flagged as
experimental in the documentation: push parsers, default %printer and
%destructor (typed: <*> and untyped: <>), %define api.value.type union and
variant, Java parsers, XML output, LR family (lr, ielr, lalr), and
semantic predicates (%?).
** Bug fixes
*** GLR: Predicates support broken by #line directives
Predicates (%?) in GLR such as
widget:
%? {new_syntax} 'w' id new_args
| %?{!new_syntax} 'w' id old_args
were issued with #lines in the middle of C code.
*** Printer and destructor with broken #line directives
The #line directives were not properly escaped when emitting the code for
%printer/%destructor, which resulted in compiler errors if there are
backslashes or double-quotes in the grammar file name.
*** Portability on ICC
The Intel compiler claims compatibility with GCC, yet rejects its _Pragma.
Generated parsers now work around this.
*** Various
There were several small fixes in the test suite and in the build system,
many warnings in bison and in the generated parsers were eliminated. The
documentation also received its share of minor improvements.
Useless code was removed from C++ parsers, and some of the generated
constructors are more 'natural'.
Changelog:
* Noteworthy changes in release 3.0.5 (2018-05-27) [stable]
** Bug fixes
*** C++: Fix support of 'syntax_error'
One incorrect 'inline' resulted in linking errors about the constructor of
the syntax_error exception.
*** C++: Fix warnings
GCC 7.3 (with -O1 or -O2 but not -O0 or -O3) issued null-dereference
warnings about yyformat being possibly null. It also warned about the
deprecated implicit definition of copy constructors when there's a
user-defined (copy) assignment operator.
*** Location of errors
In C++ parsers, out-of-bounds errors can happen when a rule with an empty
ride-hand side raises a syntax error. The behavior of the default parser
(yacc.c) in such a condition was undefined.
Now all the parsers match the behavior of glr.c: @$ is used as the
location of the error. This handles gracefully rules with and without
rhs.
*** Portability fixes in the test suite
On some platforms, some Java and/or C++ tests were failing.
Relates to PR pkg/53826, further details are provided there. This is a
temporary fix: the newest release of Bison addresses this by including
a newer version of gnulib. I'm applying this less obtrusive change for
now. No PKGREVISION, because there should be no change to existing
packages, it addresses build failures only.
Issues found with existing distfiles:
distfiles/eclipse-sourceBuild-srcIncluded-3.0.1.zip
distfiles/fortran-utils-1.1.tar.gz
distfiles/ivykis-0.39.tar.gz
distfiles/enum-1.11.tar.gz
distfiles/pvs-3.2-libraries.tgz
distfiles/pvs-3.2-linux.tgz
distfiles/pvs-3.2-solaris.tgz
distfiles/pvs-3.2-system.tgz
No changes made to these distinfo files.
Otherwise, existing SHA1 digests verified and found to be the same on
the machine holding the existing distfiles (morden). All existing
SHA1 digests retained for now as an audit trail.
* Noteworthy changes in release 3.0.4 (2015-01-23) [stable]
** Bug fixes
*** C++ with Variants (lalr1.cc)
Fix a compiler warning when no %destructor use $$.
*** Test suites
Several portability issues in tests were fixed.
(pkgsrc)
- Add comment on patch-lib_isnan.c (from cvs log)
(upstream)
- Update devel/bison 3.0.2 to 3.0.3
Thanks obache and wiz for review.
---------------------------------
* Noteworthy changes in release 3.0.3 (2015-01-15) [stable]
** Bug fixes
*** C++ with Variants (lalr1.cc)
Problems with %destructor and '%define parse.assert' have been fixed.
*** Named %union support (yacc.c, glr.c)
Bison 3.0 introduced a regression on named %union such as
%union foo { int ival; };
The possibility to use a name was introduced "for Yacc compatibility".
It is however not required by POSIX Yacc, and its usefulness is not clear.
*** %define api.value.type union with %defines (yacc.c, glr.c)
The C parsers were broken when %defines was used together with "%define
api.value.type union".
*** Redeclarations are reported in proper order
On
%token FOO "foo"
%printer {} "foo"
%printer {} FOO
bison used to report:
/tmp/foo.yy:2.10-11: error: %printer redeclaration for FOO
%printer {} "foo"
^^
/tmp/foo.yy:3.10-11: previous declaration
%printer {} FOO
^^
Now, the "previous" declaration is always the first one.
** Documentation
Bison now installs various files in its docdir (which defaults to
'/usr/local/share/doc/bison'), including the three fully blown examples
extracted from the documentation:
- rpcalc
Reverse polish calculator, a simple introductory example.
- mfcalc
Multi-function Calc, a calculator with memory and functions and located
error messages.
- calc++
a calculator in C++ using variant support and token constructors.
Do it for all packages that
* mention perl, or
* have a directory name starting with p5-*, or
* depend on a package starting with p5-
like last time, for 5.18, where this didn't lead to complaints.
Let me know if you have any this time.
* Noteworthy changes in release 3.0.2 (2013-12-05) [stable]
** Bug fixes
*** Generated source files when errors are reported
When warnings are issued and -Werror is set, bison would still generate
the source files (*.c, *.h...). As a consequence, some runs of "make"
could fail the first time, but not the second (as the files were generated
anyway).
This is fixed: bison no longer generates this source files, but, of
course, still produces the various reports (*.output, *.xml, etc.).
*** %empty is used in reports
Empty right-hand sides are denoted by '%empty' in all the reports (text,
dot, XML and formats derived from it).
*** YYERROR and variants
When C++ variant support is enabled, an error triggered via YYERROR, but
not caught via error recovery, resulted in a double deletion.
* Noteworthy changes in release 3.0.1 (2013-11-12) [stable]
** Bug fixes
*** Errors in caret diagnostics
On some platforms, some errors could result in endless diagnostics.
*** Fixes of the -Werror option
Options such as "-Werror -Wno-error=foo" were still turning "foo"
diagnostics into errors instead of warnings. This is fixed.
Actually, for consistency with GCC, "-Wno-error=foo -Werror" now also
leaves "foo" diagnostics as warnings. Similarly, with "-Werror=foo
-Wno-error", "foo" diagnostics are now errors.
*** GLR Predicates
As demonstrated in the documentation, one can now leave spaces between
"%?" and its "{".
*** Installation
The yacc.1 man page is no longer installed if --disable-yacc was
specified.
*** Fixes in the test suite
Bugs and portability issues.
* Noteworthy changes in release 3.0 (2013-07-25) [stable]
** 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.
The generated C parsers still aim at C90.
** Backward incompatible changes
*** Obsolete features
Support for YYFAIL is removed (deprecated in Bison 2.4.2): use YYERROR.
Support for yystype and yyltype is removed (deprecated in Bison 1.875):
use YYSTYPE and YYLTYPE.
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)
The glr.c skeleton uses defines such as #define yylval (yystackp->yyval) in
generated code. These weren't properly undefined before the inclusion of
the user epilogue, so functions such as the following were butchered by the
preprocessor expansion:
int yylex (YYSTYPE *yylval);
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
Santet.
*** Carets
Version 2.7 introduced caret errors, for a prettier output. These are now
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
warnings as errors. The warnings need not have been explicitly activated
using the -W option, this is similar to what GCC 4.7 does.
For example, given the following command line, Bison will treat both
warnings related to POSIX Yacc incompatibilities and S/R conflicts as
errors (and only those):
$ bison -Werror=yacc,error=conflicts-sr input.y
If no categories are specified, -Werror will make all active warnings into
errors. For example, the following line does the same the previous example:
$ bison -Werror -Wnone -Wyacc -Wconflicts-sr input.y
(By default -Wconflicts-sr,conflicts-rr,deprecated,other is enabled.)
Note that the categories in this -Werror option may not be prefixed with
"no-". However, -Wno-error[=CATEGORY] is valid.
Note that -y enables -Werror=yacc. Therefore it is now possible to require
Yacc-like behavior (e.g., always generate y.tab.c), but to report
incompatibilities as warnings: "-y -Wno-error=yacc".
*** The display of warnings is now richer
The option that controls a given warning is now displayed:
foo.y:4.6: warning: type clash on default action: <foo> != <bar> [-Wother]
In the case of warnings treated as errors, the prefix is changed from
"warning: " to "error: ", and the suffix is displayed, in a manner similar
to GCC, as [-Werror=CATEGORY].
For instance, where the previous version of Bison would report (and exit
with failure):
bison: warnings being treated as errors
input.y:1.1: warning: stray ',' treated as white space
it now reports:
input.y:1.1: error: stray ',' treated as white space [-Werror=other]
*** Deprecated constructs
The new 'deprecated' warning category flags obsolete constructs whose
support will be discontinued. It is enabled by default. These warnings
used to be reported as 'other' warnings.
*** 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
*** Undefined but unused symbols
Bison used to raise an error for undefined symbols that are not used in
the grammar. This is now only a warning.
%printer {} symbol1
%destructor {} symbol2
%type <type> symbol3
%%
exp: "a";
*** 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>
*** Conflicts
The warnings and error messages about shift/reduce and reduce/reduce
conflicts have been normalized. For instance on the following foo.y file:
%glr-parser
%%
exp: exp '+' exp | '0' | '0';
compare the previous version of bison:
$ bison foo.y
foo.y: conflicts: 1 shift/reduce, 2 reduce/reduce
$ bison -Werror foo.y
bison: warnings being treated as errors
foo.y: conflicts: 1 shift/reduce, 2 reduce/reduce
with the new behavior:
$ bison foo.y
foo.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
foo.y: warning: 2 reduce/reduce conflicts [-Wconflicts-rr]
$ bison -Werror foo.y
foo.y: error: 1 shift/reduce conflict [-Werror=conflicts-sr]
foo.y: error: 2 reduce/reduce conflicts [-Werror=conflicts-rr]
When %expect or %expect-rr is used, such as with bar.y:
%expect 0
%glr-parser
%%
exp: exp '+' exp | '0' | '0';
Former behavior:
$ bison bar.y
bar.y: conflicts: 1 shift/reduce, 2 reduce/reduce
bar.y: expected 0 shift/reduce conflicts
bar.y: expected 0 reduce/reduce conflicts
New one:
$ bison bar.y
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
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}
** 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
the generated files. This is especially useful to avoid collisions
with identifiers in the target language. For instance
%token FILE for ERROR
%define api.token.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.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
%error-verbose directive is deprecated in favor of "%define parse.error
verbose".
** Renamed %define variables
The following variables have been renamed for consistency. Backward
compatibility is ensured, but upgrading is recommended.
lr.default-reductions -> lr.default-reduction
lr.keep-unreachable-states -> lr.keep-unreachable-state
namespace -> api.namespace
stype -> api.value.type
** Semantic predicates
Contributed by Paul Hilfinger.
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 run-time
expressions.
** The directive %expect-rr is now an error in non GLR mode
It used to be an error only if used in non GLR mode, _and_ if there are
reduce/reduce conflicts.
** 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.
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 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
hinder the comprehension of a new grammar: one will wonder about the role
of a precedence, where in fact it is useless. The following changes aim
at detecting and reporting these extra directives.
*** Precedence warning category
A new category of warning, -Wprecedence, was introduced. It flags the
useless precedence and associativity directives.
*** Useless associativity
Bison now warns about symbols with a declared associativity that is never
used to resolve conflicts. In that case, using %precedence is sufficient;
the parsing tables will remain unchanged. Solving these warnings may raise
useless precedence warnings, as the symbols no longer have associativity.
For example:
%left '+'
%left '*'
%%
exp:
"number"
| exp '+' "number"
| exp '*' exp
;
will produce a
warning: useless associativity for '+', use %precedence [-Wprecedence]
%left '+'
^^^
*** Useless precedence
Bison now warns about symbols with a declared precedence and no declared
associativity (i.e., declared with %precedence), and whose precedence is
never used. In that case, the symbol can be safely declared with %token
instead, without modifying the parsing tables. For example:
%precedence '='
%%
exp: "var" '=' "number";
will produce a
warning: useless precedence for '=' [-Wprecedence]
%precedence '='
^^^
*** Useless precedence and associativity
In case of both useless precedence and associativity, the issue is flagged
as follows:
%nonassoc '='
%%
exp: "var" '=' "number";
The warning is:
warning: useless precedence and associativity for '=' [-Wprecedence]
%nonassoc '='
^^^
** Empty rules
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.
The Java skeleton now supports push parsing.
Contributed by Dennis Heimbigner.
** C++ skeletons improvements
*** The parser header is no longer mandatory (lalr1.cc, glr.cc)
Using %defines is now optional. Without it, the needed support classes
are defined in the generated parser, instead of additional files (such as
location.hh, position.hh and stack.hh).
*** Locations are no longer mandatory (lalr1.cc, glr.cc)
Both lalr1.cc and glr.cc no longer require %location.
*** syntax_error exception (lalr1.cc)
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).
*** %define api.value.type variant
This is based on a submission from Michiel De Wilde. With help
from Théophile Ranquet.
In this mode, complex C++ objects can be used as semantic values. For
instance:
%token <::std::string> TEXT;
%token <int> NUMBER;
%token SEMICOLON ";"
%type <::std::string> item;
%type <::std::list<std::string>> list;
%%
result:
list { std::cout << $1 << std::endl; }
;
list:
%empty { /* Generates an empty string list. */ }
| list item ";" { std::swap ($$, $1); $$.push_back ($2); }
;
item:
TEXT { std::swap ($$, $1); }
| NUMBER { $$ = string_cast ($1); }
;
*** %define api.token.constructor
When variants are enabled, Bison can generate functions to build the
tokens. This guarantees that the token type (e.g., NUMBER) is consistent
with the semantic value (e.g., int):
parser::symbol_type yylex ()
{
parser::location_type loc = ...;
...
return parser::make_TEXT ("Hello, world!", loc);
...
return parser::make_NUMBER (42, loc);
...
return parser::make_SEMICOLON (loc);
...
}
*** C++ locations
There are operator- and operator-= for 'location'. Negative line/column
increments can no longer underflow the resulting value.
* Noteworthy changes in release 2.7 (2012-12-12) [stable]
** Bug fixes
Warnings about uninitialized yylloc in yyparse have been fixed.
Restored C90 compliance (yet no report was ever made).
** Diagnostics are improved
*** Changes in the format of error messages
This used to be the format of many error reports:
input.y:2.7-12: %type redeclaration for exp
input.y:1.7-12: previous declaration
It is now:
input.y:2.7-12: error: %type redeclaration for exp
input.y:1.7-12: previous declaration
*** New format for error reports: carets
Caret errors have been added to Bison:
input.y:2.7-12: error: %type redeclaration for exp
%type <sval> exp
^^^^^^
input.y:1.7-12: previous declaration
%type <ival> exp
^^^^^^
or
input.y:3.20-23: error: ambiguous reference: '$exp'
exp: exp '+' exp { $exp = $1 + $3; };
^^^^
input.y:3.1-3: refers to: $exp at $$
exp: exp '+' exp { $exp = $1 + $3; };
^^^
input.y:3.6-8: refers to: $exp at $1
exp: exp '+' exp { $exp = $1 + $3; };
^^^
input.y:3.14-16: refers to: $exp at $3
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
will be made the default behavior (but may still be deactivated with
-fno-caret).
** New value for %define variable: api.pure full
The %define variable api.pure requests a pure (reentrant) parser. However,
for historical reasons, using it in a location-tracking Yacc parser
resulted in a yyerror function that did not take a location as a
parameter. With this new value, the user may request a better pure parser,
where yyerror does take a location as a parameter (in location-tracking
parsers).
The use of "%define api.pure true" is deprecated in favor of this new
"%define api.pure full".
** New %define variable: api.location.type (glr.cc, lalr1.cc, lalr1.java)
The %define variable api.location.type defines the name of the type to use
for locations. When defined, Bison no longer generates the position.hh
and location.hh files, nor does the parser will include them: the user is
then responsible to define her type.
This can be used in programs with several parsers to factor their location
and position files: let one of them generate them, and the others just use
them.
This feature was actually introduced, but not documented, in Bison 2.5,
under the name "location_type" (which is maintained for backward
compatibility).
For consistency, lalr1.java's %define variables location_type and
position_type are deprecated in favor of api.location.type and
api.position.type.
** Exception safety (lalr1.cc)
The parse function now catches exceptions, uses the %destructors to
release memory (the lookahead symbol and the symbols pushed on the stack)
before re-throwing the exception.
This feature is somewhat experimental. User feedback would be
appreciated.
** Graph improvements in DOT and XSLT
The graphical presentation of the states is more readable: their shape is
now rectangular, the state number is clearly displayed, and the items are
numbered and left-justified.
The reductions are now explicitly represented as transitions to other
diamond shaped nodes.
These changes are present in both --graph output and xml2dot.xsl XSLT
processing, with minor (documented) differences.
** %language is no longer an experimental feature.
The introduction of this feature, in 2.4, was four years ago. The
--language option and the %language directive are no longer experimental.
** Documentation
The sections about shift/reduce and reduce/reduce conflicts resolution
have been fixed and extended.
Although introduced more than four years ago, XML and Graphviz reports
were not properly documented.
The translation of mid-rule actions is now described.
* Noteworthy changes in release 2.6.5 (2012-11-07) [stable]
We consider compiler warnings about Bison generated parsers to be bugs.
Rather than working around them in your own project, please consider
reporting them to us.
** Bug fixes
Warnings about uninitialized yylval and/or yylloc for push parsers with a
pure interface have been fixed for GCC 4.0 up to 4.8, and Clang 2.9 to
3.2.
Other issues in the test suite have been addressed.
Nul 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.
* Noteworthy changes in release 2.6.4 (2012-10-23) [stable]
Bison 2.6.3's --version was incorrect. This release fixes this issue.
* Noteworthy changes in release 2.6.3 (2012-10-22) [stable]
** Bug fixes
Bugs and portability issues in the test suite have been fixed.
Some errors in translations have been addressed, and --help now directs
users to the appropriate place to report them.
Stray Info files shipped by accident are removed.
Incorrect definitions of YY_, issued by yacc.c when no parser header is
generated, are removed.
All the generated headers are self-contained.
** Header guards (yacc.c, glr.c, glr.cc)
In order to avoid collisions, the header guards are now
YY_<PREFIX>_<FILE>_INCLUDED, instead of merely <PREFIX>_<FILE>.
For instance the header generated from
%define api.prefix "calc"
%defines "lib/parse.h"
will use YY_CALC_LIB_PARSE_H_INCLUDED as guard.
** Fix compiler warnings in the generated parser (yacc.c, glr.c)
The compilation of pure parsers (%define api.pure) can trigger GCC
warnings such as:
input.c: In function 'yyparse':
input.c:1503:12: warning: 'yylval' may be used uninitialized in this
function [-Wmaybe-uninitialized]
*++yyvsp = yylval;
^
This is now fixed; pragmas to avoid these warnings are no longer needed.
Warnings from clang ("equality comparison with extraneous parentheses" and
"function declared 'noreturn' should not return") have also been
addressed.
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