[pypy-issue] Issue #2459: AssertionError in parse_ebnf when nesting + and [] (pypy/pypy)

Tim Baanen issues-reply at bitbucket.org
Sat Dec 31 10:02:53 EST 2016


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?




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