New issue 2459: AssertionError in parse_ebnf when nesting + and []
https://bitbucket.org/pypy/pypy/issues/2459/assertionerror-in-parse_ebnf-when-nesting
Tim Baanen:
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:
```
#!python
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?
_______________________________________________
pypy-issue mailing list
pypy-issue@python.org
https://mail.python.org/mailman/listinfo/pypy-issue
