b7aab2dbad
Reported by Agency for Defense Development. https://lists.gnu.org/r/bug-bison/2020-08/msg00008.html On an empty such as %token FOO BAR FOO 0 %% input: %empty we crash because when we find FOO 0, we decrement ntokens (since FOO was discovered to be EOF, which is already known to be a token, so we increment ntokens for it, and need to cancel this). This "works well" when EOF is properly defined in one go, but here it is first defined and later only assign token code 0. In the meanwhile BAR was given the token number that we just decremented. To fix this, assign symbol numbers after parsing, not during parsing, so that we also saw all the explicit token codes. To maintain the current numbers (I'd like to keep no difference in the output, not just equivalence), we need to make sure the symbols are numbered in the same order: that of appearance in the source file. So we need the locations to be correct, which was almost the case, except for nterms that appeared several times as LHS (i.e., several times as "foo: ..."). Fixing the use of location_of_lhs sufficed (it appears it was intended for this use, but its implementation was unfinished: it was always set to "false" only). * src/symtab.c (symbol_location_as_lhs_set): Update location_of_lhs. (symbol_code_set): Remove broken hack that decremented ntokens. (symbol_class_set, dummy_symbol_get): Don't set number, ntokens and nnterms. (symbol_check_defined): Do it. (symbols): Don't count nsyms here. Actually, don't count nsyms at all: let it be done in... * src/reader.c (check_and_convert_grammar): here. Define nsyms from ntokens and nnterms after parsing. * tests/input.at (EOF redeclared): New. * examples/c/bistromathic/bistromathic.test: Adjust the traces: in "%nterm <double> exp %% input: ...", exp used to be numbered before input.
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/.
Installation
Build from git
The README-hacking.md file is about building, modifying and checking Bison. See its "Working from the Repository" section to build Bison from the git repo. Roughly, run:
$ git submodule update --init
$ ./bootstrap
then proceed with the usual configure && make steps.
Build from tarball
See the [INSTALL file](INSTALL] for generic compilation and installation instructions.
Bison requires GNU m4 1.4.6 or later. See https://ftp.gnu.org/gnu/m4/m4-1.4.6.tar.gz.
Running a non installed bison
Once you ran make, you might want to toy with this fresh bison before
installing it. In that case, do not use src/bison: it would use the
installed files (skeletons, etc.), not the local ones. Use tests/bison.
Colored diagnostics
As an experimental feature, diagnostics are now colored, controlled by the
--color and --style options.
To use them, install the libtextstyle library, 0.20.5 or newer, before configuring Bison. It is available from https://alpha.gnu.org/gnu/gettext/, for instance https://alpha.gnu.org/gnu/gettext/libtextstyle-0.20.5.tar.gz, or as part of Gettext 0.21 or newer, for instance https://ftp.gnu.org/gnu/gettext/gettext-0.21.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, say bison-bw.css, 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.
In some diagnostics, bison uses libtextstyle to emit special escapes to
generate clickable hyperlinks. The environment variable
NO_TERM_HYPERLINKS can be used to suppress them. This may be useful for
terminal emulators which produce garbage output when they receive the escape
sequence for a hyperlink. Currently (as of 2020), this affects some versions
of emacs, guake, konsole, lxterminal, rxvt, yakuake.
Relocatability
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 symlinks to the installed and moved programs, and invoke them through the symlink.
See "Enabling Relocatability" in the documentation.
Internationalization
Bison supports two catalogs: one for Bison itself (i.e., for the maintainer-side parser generation), and one for the generated parsers (i.e., for the user-side parser execution). The requirements between both differ: bison needs ngettext, the generated parsers do not. To simplify the build system, neither are installed if ngettext is not supported, even if generated parsers could have been localized. See http://lists.gnu.org/archive/html/bug-bison/2009-08/msg00006.html for more details.
Questions
See the section FAQ in the documentation (doc/bison.info) for frequently
asked questions. The documentation is also available in PDF and HTML,
provided you have a recent version of Texinfo installed: run make pdf or
make html.
If you have questions about using Bison and the documentation does not answer them, please send mail to help-bison@gnu.org.
Bug reports
Please send bug reports to bug-bison@gnu.org. Be sure to include the
version number from bison --version, and a complete, self-contained test
case in each bug report.
Copyright statements
For any copyright year range specified as YYYY-ZZZZ in this package, note that the range specifies every single year in that closed interval.