We are happy to announce the release of Bison 3.4. A particular focus was put on improving the diagnostics, which are now colored by default, and accurate with multibyte input. Their format was also changed, and is now similar to GCC 9's diagnostics.
Users of the default backend (yacc.c) can use the new %define variable api.header.include to avoid duplicating the content of the generated header in the generated parser. There are two new examples installed, including a reentrant calculator which supports recursive calls to the parser and Flex-generated scanner. See below for more details. ================================================================== 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. Here is the GNU Bison home page: https://gnu.org/software/bison/ ================================================================== Here are the compressed sources: https://ftp.gnu.org/gnu/bison/bison-3.4.tar.gz (4.1MB) https://ftp.gnu.org/gnu/bison/bison-3.4.tar.xz (3.1MB) Here are the GPG detached signatures[*]: https://ftp.gnu.org/gnu/bison/bison-3.4.tar.gz.sig https://ftp.gnu.org/gnu/bison/bison-3.4.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-3.4.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 2.69 Automake 1.16.1 Flex 2.6.4 Gettext 0.19.8.1 Gnulib v0.1-2563-gd654989d8 ================================================================== NEWS * 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. -- If you have a working or partly working program that you'd like to offer to the GNU project as a GNU package, see https://www.gnu.org/help/evaluation.html.
