Hi everyone,
This is a copy of an issue I filed at your issue tracker,
https://bitbucket.org/pypy/pypy/issues/2459/assertionerror-in-parse_ebnf-
when-nesting, where I was told to report it to the mailing list. I was
using the rlib.parsing module for parsing a simple language, but I ran into
an AssertionError which I can't explain (from the documentation, at least).
It seems to occur whenever a symbol like `+` or `*` is used inside `[]`
brackets. Here is an example file:
from rpython.rlib.parsing.ebnfparse import parse_ebnf
> regexes, rules, ToAST = parse_ebnf("""
> test: ["foo"+] "bar";
> """)
>
When I run this code, both on the default branch and on the
`release-pypy2.7-v5.6.0` branch, the following error occurs:
test/test_parser.py:10: in <module>
> """)
> pypy/rpython/rlib/parsing/ebnfparse.py:57: in parse_ebnf
> s.visit(visitor)
> pypy/rpython/rlib/parsing/tree.py:86: in visit
> return getattr(visitor, "visit_" + self.symbol)(self)
> pypy/rpython/rlib/parsing/ebnfparse.py:110: in visit_file
> return node.children[0].visit(self)
> pypy/rpython/rlib/parsing/tree.py:86: in visit
> return getattr(visitor, "visit_" + self.symbol)(self)
> pypy/rpython/rlib/parsing/ebnfparse.py:114: in visit_list
> child.visit(self)
> pypy/rpython/rlib/parsing/tree.py:86: in visit
> return getattr(visitor, "visit_" + self.symbol)(self)
> pypy/rpython/rlib/parsing/ebnfparse.py:131: in visit_production
> expansions = node.children[2].visit(self)
> pypy/rpython/rlib/parsing/tree.py:86: in visit
> return getattr(visitor, "visit_" + self.symbol)(self)
> pypy/rpython/rlib/parsing/ebnfparse.py:146: in visit_body
> expansion = child.visit(self)
> pypy/rpython/rlib/parsing/tree.py:86: in visit
> return getattr(visitor, "visit_" + self.symbol)(self)
> pypy/rpython/rlib/parsing/ebnfparse.py:153: in visit_expansion
> expansion = child.visit(self)
> pypy/rpython/rlib/parsing/tree.py:86: in visit
> return getattr(visitor, "visit_" + self.symbol)(self)
> pypy/rpython/rlib/parsing/ebnfparse.py:161: in visit_enclosed
> assert change == " " or change == newchange
> AssertionError
>
Commenting out the assertion that is failing doesn't seem to cause any
problems and the resulting parser has the right behavior. My current
workaround is to make a new terminal symbol that behaves like `"foo"+` in
the example code, which appears to work but is somewhat less readable.
Did I miss something or is this an actual bug in RPython and/or its
documentation?
Thanks in advance!
Tim
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