330552ea49
Currently when a push parser finishes its parsing (i.e., it did not
return YYPUSH_MORE), it also clears its state. It is therefore
impossible to see if it had parse errors.
In the context of autocompletion, because error recovery might have
fired, the parser is actually already in a different state. For
instance on `(1 + + <TAB>` in the bistromathic, because there's a
`exp: "(" error ")"` recovery rule, `1 + +` tokens have already been
popped, replaced by `error`, and autocompletions think we are ready
for the closing ")". So here, we would like to see if there was a
syntax error, yet `yynerrs` was cleared.
In the case of a successful parse, we still have a problem: if error
recovery succeeded, we won't know it, since, again, `yynerrs` is
clearer.
It seems much more natural to leave the parser state available for
analysis when there is a failure.
To reuse the parser, we should either:
1. provide an explicit means to reinitialize a parser state for future
parses.
2. automatically reset the parser state when it is used in a new
parse.
Option 2 requires to check whether we need to reinitialize the parser
each time we call `yypush_parse`, i.e., each time we give a new token.
This seems expensive compared to Option 1, but benchmarks revealed no
difference. Option 1 is incompatible with the documentation
("After `yypush_parse` returns a status other than `YYPUSH_MORE`, the
parser instance `yyps` may be reused for a new parse.").
So Option 2 wins, reusing the private `yynew` member to record that a
parse was finished, and therefore that the state must reset in the
next call to `yypull_parse`.
While at it, this implementation now reuses the previously enlarged
stacks from one parse to another.
* data/skeletons/yacc.c (yypstate_new): Set up the stacks in their
initial configurations (setting their bottom to the stack array), and
use yypstate_clear to reset them (moving their top to their bottom).
(yypstate_delete): Adjust.
(yypush_parse): At the beginning, clear yypstate if needed, and at the
end, record when yypstate needs to be clearer.
* examples/c/bistromathic/parse.y (expected_tokens): Do not propose
autocompletion when there are parse errors.
* examples/c/bistromathic/bistromathic.test: Check that case.
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 before configuring Bison. It is available from https://alpha.gnu.org/gnu/gettext/, for instance https://alpha.gnu.org/pub/gnu/gettext/libtextstyle-0.20.5.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.
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.