GNU Bison NEWS

* 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
  failures.

  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).

  Some unlikely crashes found by fuzzing have been fixed.  This is only
  about bison itself, not the generated parsers.


* 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

