Hi!
This bug fix release addresses portability issues of Bison 3.7, including with versions of libtextstyle. See the NEWS below for more details. Bison 3.7 introduced the generation of counterexamples for conflicts, contributed by Vincent Imbimbo. For instance on a grammar featuring the infamous "dangling else" problem, "bison -Wcounterexamples" now gives: $ bison -Wcounterexamples else.y 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 Reduce derivation exp ↳ "if" exp "then" exp "else" exp ↳ "if" exp "then" exp • which actually proves that the grammar is ambiguous by exhibiting a text sample with two parse trees. Cheers! ================================================================== Here are the compressed sources: https://ftp.gnu.org/gnu/bison/bison-3.7.1.tar.gz (5.1MB) https://ftp.gnu.org/gnu/bison/bison-3.7.1.tar.lz (3.1MB) https://ftp.gnu.org/gnu/bison/bison-3.7.1.tar.xz (3.1MB) Here are the GPG detached signatures[*]: https://ftp.gnu.org/gnu/bison/bison-3.7.1.tar.gz.sig https://ftp.gnu.org/gnu/bison/bison-3.7.1.tar.lz.sig https://ftp.gnu.org/gnu/bison/bison-3.7.1.tar.xz.sig Use a mirror for higher download bandwidth: https://www.gnu.org/order/ftp.html [*] Use a .sig file to verify that the corresponding file (without the .sig suffix) is intact. First, be sure to download both the .sig file and the corresponding tarball. Then, run a command like this: gpg --verify bison-3.7.1.tar.gz.sig If that command fails because you don't have the required public key, then run this command to import it: gpg --keyserver keys.gnupg.net --recv-keys 0DDCAA3278D5264E and rerun the 'gpg --verify' command. This release was bootstrapped with the following tools: Autoconf 2.69b.24-e9bfc Automake 1.16b Flex 2.6.4 Gettext 0.20.1.153-6c39c Gnulib v0.1-3684-g37b6f1294 ================================================================== GNU Bison is a general-purpose parser generator that converts an annotated context-free grammar into a deterministic LR or generalized LR (GLR) parser employing LALR(1) parser tables. Bison can also generate IELR(1) or canonical LR(1) parser tables. Once you are proficient with Bison, you can use it to develop a wide range of language parsers, from those used in simple desk calculators to complex programming languages. Bison is upward compatible with Yacc: all properly-written Yacc grammars work with Bison with no change. Anyone familiar with Yacc should be able to use Bison with little trouble. You need to be fluent in C, C++ or Java programming in order to use Bison. Bison and the parsers it generates are portable, they do not require any specific compilers. GNU Bison's home page is https://gnu.org/software/bison/. ================================================================== * 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.