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re2c option -F (flex syntax) broken #229

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genivia-inc opened this issue Nov 4, 2018 · 4 comments
Closed

re2c option -F (flex syntax) broken #229

genivia-inc opened this issue Nov 4, 2018 · 4 comments

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@genivia-inc
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@genivia-inc genivia-inc commented Nov 4, 2018

re2x -F (Flex syntax) version 1.1.1 throws a syntax error for the regex (a|ab)ba but the regex (a|ab)(ba) works fine for some reason. This is valid Flex syntax.

I can work around this issue for now by using regex ("a"|"ab")"ba", but it would be nice if re2c accepts Flex syntax.

@skvadrik
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@skvadrik skvadrik commented Nov 5, 2018

This does look like an error to me. But this behaviour goes back as far as re2c-0.13.6 (and supposedly before that), and Flex syntax has always been only vaguely defined in re2c. I first need to understand what re2c already supports (otherwise the fix may break someone else's code), and then see how we can fix that without introducing ambiguity in grammar.

There is another workaround. This causes syntax error:

/*!re2c
    (a|ab)ba {}
*/

But this doesn't (indentation doesn't matter as long as the code in braces is on a new line):

/*!re2c
    (a|ab)ba
    {}
*/

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@genivia-inc
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@genivia-inc genivia-inc commented Nov 5, 2018

Thanks for the suggestion. With the { } code block on the same line it is strange that any character after a ), ], * or + in the regex causes this failure, e.g. (a)b and [a]b and a*b and a+b fail.

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@skvadrik
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@skvadrik skvadrik commented Nov 6, 2018

@genivia-inc It's not the special characters ), ], *, + that cause the error, it's the raw character at the end of the regexp followed by one or more spaces and the opening brace {. This simple example also fails:

/*!re2c
    a {}
*/

The reason why it fails is partly historical: partial support for flex syntax was added on top of already existing re2c-specific syntax, which caused parsing conflicts (some due to limitations in the implementation, some due to genuine ambiguity in grammar).

I have a fix for the original example, but I want to make sure that it doesn't break existing code and check similar cases.

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skvadrik added a commit that referenced this issue Nov 14, 2018
This fixes bug #229: re2c option -F (flex syntax) broken,
reported by Robert van Engelen.

A well-formed example that caused syntax error (flex-style raw literal
followed by one or more spaces and a curly brace):

/*!re2c
    a {}
*/

The faulty behaviour goes back as far as re2c-0.13.6 (and supposedly
before that): in flex mode, raw literal may occur in various contexts
both as a regexp (string literal) and an identifier (named definition,
condiiton name). RE2C uses lookahead to infer the context and determine
the appropriate type of lexer token, but it missed some cases.

The fix has two sides. First, if reduces the number of contexts where
the general lexer may encounter raw literal (by using specialized lexers
for condition lists <x,y,...,z> and condition goto => and :=>). Second,
it fixes the lookahead regexps used for context inference.

Also added a bunch of tests (generated by a script).
@skvadrik
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@skvadrik skvadrik commented Nov 14, 2018

@genivia-inc This should fix your example (and a couple of other cases in -F mode): 30a0682

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@skvadrik skvadrik closed this Jan 16, 2019
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this issue Sep 20, 2020
2.0.3 (2020-08-22)
~~~~~~~~~~~~~~~~~~

- Fix issues when building re2c as a CMake subproject
  (`#302 <https://github.com/skvadrik/re2c/pull/302>`_:

- Final corrections in the SIMPA article "RE2C: A lexer generator based on
  lookahead-TDFA", https://doi.org/10.1016/j.simpa.2020.100027

2.0.2 (2020-08-08)
~~~~~~~~~~~~~~~~~~

- Enable re2go building by default.

- Package CMake files into release tarball.

2.0.1 (2020-07-29)
~~~~~~~~~~~~~~~~~~

- Updated version for CMake build system (forgotten in release 2.0).

- Added a short article about re2c for the Software Impacts journal.

2.0 (2020-07-20)
~~~~~~~~~~~~~~~~

- Added new code generation backend for Go and a new ``re2go`` program
  (`#272 <https://github.com/skvadrik/re2c/issues/272>`_: Go support).
  Added option ``--lang <c | go>``.

- Added CMake build system as an alternative to Autotools
  (`#275 <https://github.com/skvadrik/re2c/pull/275>`_:
  Add a CMake build system (thanks to ligfx),
  `#244 <https://github.com/skvadrik/re2c/issues/244>`_: Switching to CMake).

- Changes in generic API:

  + Removed primitives ``YYSTAGPD`` and ``YYMTAGPD``.
  + Added primitives ``YYSHIFT``, ``YYSHIFTSTAG``, ``YYSHIFTMTAG``
    that allow to express fixed tags in terms of generic API.
  + Added configurations ``re2c:api:style`` and ``re2c:api:sigil``.
  + Added named placeholders in interpolated configuration strings.

- Changes in reuse mode (``-r, --reuse`` option):

  + Do not reset API-related configurations in each `use:re2c` block
    (`#291 <https://github.com/skvadrik/re2c/issues/291>`_:
    Defines in rules block are not propagated to use blocks).
  + Use block-local options instead of last block options.
  + Do not accumulate options from rules/reuse blocks in whole-program options.
  + Generate non-overlapping YYFILL labels for reuse blocks.
  + Generate start label for each reuse block in storable state mode.

- Changes in start-conditions mode (``-c, --start-conditions`` option):

  + Allow to use normal (non-conditional) blocks in `-c` mode
    (`#263 <https://github.com/skvadrik/re2c/issues/263>`_:
    allow mixing conditional and non-conditional blocks with -c,
    `#296 <https://github.com/skvadrik/re2c/issues/296>`_:
    Conditions required for all lexers when using '-c' option).
  + Generate condition switch in every re2c block
    (`#295 <https://github.com/skvadrik/re2c/issues/295>`_:
    Condition switch generated for only one lexer per file).

- Changes in the generated labels:

  + Use ``yyeof`` label prefix instead of ``yyeofrule``.
  + Use ``yyfill`` label prefix instead of ``yyFillLabel``.
  + Decouple start label and initial label (affects label numbering).

- Removed undocumented configuration ``re2c🎏o``, ``re2c🎏output``.

- Changes in ``re2c🎏t``, ``re2c🎏type-header`` configuration:
  filename is now relative to the output file directory.

- Added option ``--case-ranges`` and configuration ``re2c🎏case-ranges``.

- Extended fixed tags optimization for the case of fixed-counter repetition.

- Fixed bugs related to EOF rule:

  + `#276 <https://github.com/skvadrik/re2c/issues/276>`_:
    Example 01_fill.re in docs is broken
  + `#280 <https://github.com/skvadrik/re2c/issues/280>`_:
    EOF rules with multiple blocks
  + `#284 <https://github.com/skvadrik/re2c/issues/284>`_:
    mismatched YYBACKUP and YYRESTORE
    (Add missing fallback states with EOF rule)

- Fixed miscellaneous bugs:

  + `#286 <https://github.com/skvadrik/re2c/issues/286>`_:
    Incorrect submatch values with fixed-length trailing context.
  + `#297 <https://github.com/skvadrik/re2c/issues/297>`_:
    configure error on ubuntu 18.04 / cmake 3.10

- Changed bootstrap process (require explicit configuration flags and a path to
  re2c executable to regenerate the lexers).

- Added internal options ``--posix-prectable <naive | complex>``.

- Added debug option ``--dump-dfa-tree``.

- Major revision of the paper "Efficient POSIX submatch extraction on NFA".

----
1.3x
----

1.3 (2019-12-14)
~~~~~~~~~~~~~~~~

- Added option: ``--stadfa``.

- Added warning: ``-Wsentinel-in-midrule``.

- Added generic API primitives:

  + ``YYSTAGPD``
  + ``YYMTAGPD``

- Added configurations:

  + ``re2c:sentinel = 0;``
  + ``re2c:define:YYSTAGPD = "YYSTAGPD";``
  + ``re2c:define:YYMTAGPD = "YYMTAGPD";``

- Worked on reproducible builds
  (`#258 <https://github.com/skvadrik/re2c/pull/258>`_:
  Make the build reproducible).

----
1.2x
----

1.2.1 (2019-08-11)
~~~~~~~~~~~~~~~~~~

- Fixed bug `#253 <https://github.com/skvadrik/re2c/issues/253>`_:
  re2c should install unicode_categories.re somewhere.

- Fixed bug `#254 <https://github.com/skvadrik/re2c/issues/254>`_:
  Turn off re2c:eof = 0.

1.2 (2019-08-02)
~~~~~~~~~~~~~~~~

- Added EOF rule ``$`` and configuration ``re2c:eof``.

- Added ``/*!include:re2c ... */`` directive and ``-I`` option.

- Added ``/*!header:re2c:on*/`` and ``/*!header:re2c:off*/`` directives.

- Added ``--input-encoding <ascii | utf8>`` option.

  + `#237 <https://github.com/skvadrik/re2c/issues/237>`_:
    Handle non-ASCII encoded characters in regular expressions
  + `#250 <https://github.com/skvadrik/re2c/issues/250>`_
    UTF8 enoding

- Added include file with a list of definitions for Unicode character classes.

  + `#235 <https://github.com/skvadrik/re2c/issues/235>`_:
    Unicode character classes

- Added ``--location-format <gnu | msvc>`` option.

  + `#195 <https://github.com/skvadrik/re2c/issues/195>`_:
    Please consider using Gnu format for error messages

- Added ``--verbose`` option that prints "success" message if re2c exits
  without errors.

- Added configurations for options:

  + ``-o --output`` (specify output file)
  + ``-t --type-header`` (specify header file)

- Removed configurations for internal/debug options.

- Extended ``-r`` option: allow to mix multiple ``/*!rules:re2c*/``,
  ``/*!use:re2c*/`` and ``/*!re2c*/`` blocks.

  + `#55 <https://github.com/skvadrik/re2c/issues/55>`_:
    allow standard re2c blocks in reuse mode

- Fixed ``-F --flex-support`` option: parsing and operator precedence.

  + `#229 <https://github.com/skvadrik/re2c/issues/229>`_:
    re2c option -F (flex syntax) broken
  + `#242 <https://github.com/skvadrik/re2c/issues/242>`_:
    Operator precedence with --flex-syntax is broken

- Changed difference operator ``/`` to apply before encoding expansion of
  operands.

  + `#236 <https://github.com/skvadrik/re2c/issues/236>`_:
    Support range difference with variable-length encodings

- Changed output generation of output file to be atomic.

  + `#245 <https://github.com/skvadrik/re2c/issues/245>`_:
    re2c output is not atomic

- Authored research paper "Efficient POSIX Submatch Extraction on NFA"
  together with Dr Angelo Borsotti.

- Added experimental libre2c library (``--enable-libs`` configure option) with
  the following algorithms:

  + TDFA with leftmost-greedy disambiguation
  + TDFA with POSIX disambiguation (Okui-Suzuki algorithm)
  + TNFA with leftmost-greedy disambiguation
  + TNFA with POSIX disambiguation (Okui-Suzuki algorithm)
  + TNFA with lazy POSIX disambiguation (Okui-Suzuki algorithm)
  + TNFA with POSIX disambiguation (Kuklewicz algorithm)
  + TNFA with POSIX disambiguation (Cox algorithm)

- Added debug subsystem (``--enable-debug`` configure option) and new debug
  options:

  + ``-dump-cfg`` (dump control flow graph of tag variables)
  + ``-dump-interf`` (dump interference table of tag variables)
  + ``-dump-closure-stats`` (dump epsilon-closure statistics)

- Added internal options:

  + ``--posix-closure <gor1 | gtop>`` (switch between shortest-path algorithms
    used for the construction of POSIX closure)

- Fixed a number of crashes found by American Fuzzy Lop fuzzer:

  + `#226 <https://github.com/skvadrik/re2c/issues/226>`_,
    `#227 <https://github.com/skvadrik/re2c/issues/227>`_,
    `#228 <https://github.com/skvadrik/re2c/issues/228>`_,
    `#231 <https://github.com/skvadrik/re2c/issues/231>`_,
    `#232 <https://github.com/skvadrik/re2c/issues/232>`_,
    `#233 <https://github.com/skvadrik/re2c/issues/233>`_,
    `#234 <https://github.com/skvadrik/re2c/issues/234>`_,
    `#238 <https://github.com/skvadrik/re2c/issues/238>`_

- Fixed handling of newlines:

  + correctly parse multi-character newlines CR LF in ``#line`` directives
  + consistently convert all newlines in the generated file to Unix-style LF

- Changed default tarball format from .gz to .xz.

  + `#221 <https://github.com/skvadrik/re2c/issues/221>`_:
    big source tarball

- Fixed a number of other bugs and resolved issues:

  + `#2 <https://github.com/skvadrik/re2c/issues/2>`_: abort
  + `#6 <https://github.com/skvadrik/re2c/issues/6>`_: segfault
  + `#10 <https://github.com/skvadrik/re2c/issues/10>`_:
    lessons/002_upn_calculator/calc_002 doesn't produce a useful example program
  + `#44 <https://github.com/skvadrik/re2c/issues/44>`_:
    Access violation when translating the attached file
  + `#49 <https://github.com/skvadrik/re2c/issues/49>`_:
    wildcard state \000 rules makes lexer behave weard
  + `#98 <https://github.com/skvadrik/re2c/issues/98>`_:
    Transparent handling of #line directives in input files
  + `#104 <https://github.com/skvadrik/re2c/issues/104>`_:
    Improve const-correctness
  + `#105 <https://github.com/skvadrik/re2c/issues/105>`_:
    Conversion of pointer parameters into references
  + `#114 <https://github.com/skvadrik/re2c/issues/114>`_:
    Possibility of fixing bug 2535084
  + `#120 <https://github.com/skvadrik/re2c/issues/120>`_:
    condition consisting of default rule only is ignored
  + `#167 <https://github.com/skvadrik/re2c/issues/167>`_:
    Add word boundary support
  + `#168 <https://github.com/skvadrik/re2c/issues/168>`_:
    Wikipedia's article on re2c
  + `#180 <https://github.com/skvadrik/re2c/issues/180>`_:
    Comment syntax?
  + `#182 <https://github.com/skvadrik/re2c/issues/182>`_:
    yych being set by YYPEEK () and then not used
  + `#196 <https://github.com/skvadrik/re2c/issues/196>`_:
    Implicit type conversion warnings
  + `#198 <https://github.com/skvadrik/re2c/issues/198>`_:
    no match for ‘operator!=’ in ‘i != std::vector<_Tp, _Alloc>::rend() [with _Tp = re2c::bitmap_t, _Alloc = std::allocator<re2c::bitmap_t>]()’
  + `#210 <https://github.com/skvadrik/re2c/issues/210>`_:
    How to build re2c in windows?
  + `#215 <https://github.com/skvadrik/re2c/issues/215>`_:
    A memory read overrun issue in s_to_n32_unsafe.cc
  + `#220 <https://github.com/skvadrik/re2c/issues/220>`_:
    src/dfa/dfa.h: simplify constructor to avoid g++-3.4 bug
  + `#223 <https://github.com/skvadrik/re2c/issues/223>`_:
    Fix typo
  + `#224 <https://github.com/skvadrik/re2c/issues/224>`_:
    src/dfa/closure_posix.cc: pack() tweaks
  + `#225 <https://github.com/skvadrik/re2c/issues/225>`_:
    Documentation link is broken in libre2c/README
  + `#230 <https://github.com/skvadrik/re2c/issues/230>`_:
    Changes for upcoming Travis' infra migration
  + `#239 <https://github.com/skvadrik/re2c/issues/239>`_:
    Push model example has wrong re2c invocation, breaks guide
  + `#241 <https://github.com/skvadrik/re2c/issues/241>`_:
    Guidance on how to use re2c for full-duplex command & response protocol
  + `#243 <https://github.com/skvadrik/re2c/issues/243>`_:
    A code generated for period (.) requires 4 bytes
  + `#246 <https://github.com/skvadrik/re2c/issues/246>`_:
    Please add a license to this repo
  + `#247 <https://github.com/skvadrik/re2c/issues/247>`_:
    Build failure on current Cygwin, probably caused by force-fed c++98 mode
  + `#248 <https://github.com/skvadrik/re2c/issues/248>`_:
    distcheck still looks for README
  + `#251 <https://github.com/skvadrik/re2c/issues/251>`_:
    Including what you use is find, but not without inclusion guards

- Updated documentation and website.
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