ParserSyntaxError on from foo import (bar \n as baz)

[Zac-HD]

import libcst as cst

code = """
from math import (nan
  as NaN)
"""
compile(code, "<string>", "exec")  # (no error)

cst.parse_module(code)             # ParserSyntaxError: Syntax Error @ 4:9.
                                   # Internal error: There must be at least one space before 'as'.

While this is really weird code, it does actually happen in the wild, e.g. here in the regex package.

[zsol]

Looks like this works with the new rust-based parser, so I likely won't fix it in the current one:

git checkout parser
cd native
printf 'from foo import (bar\n  as baaaar)' | cargo run

[zsol]

#566 contains the new parser that works with this input. After merging that, you'll need to set the following environment variable LIBCST_PARSER_TYPE=native in whatever process that runs libcst to turn on the new parser (this will be the default in a future release)

[Zac-HD]

Any indication of when the native parser will be enabled by default?

[zsol]

I'm aiming for a month or two. The parser is fairly stable at this point, and it's used to parse hundreds of millions of lines of Python at Meta. It's mostly a question of feature-completeness, the biggest gap being support for different versions of the Python grammar (these fields).