* Parse `:=` properly
* never unwrap parenthesis around `:=`
* When checking for AST-equivalence, use `ast` instead of `typed-ast` when running on python >=3.8
* Assume code that uses `:=` is at least 3.8
Based on the feedback in
https://github.com/python/black/pull/845#issuecomment-490622711
- Remove TokenizerConfig, and add a field to Grammar instead.
- Pass the Grammar to the tokenizer.
- Rename `ASYNC_IS_RESERVED_KEYWORD` to `ASYNC_KEYWORDS` and
`ASYNC_IS_VALID_IDENTIFIER` to `ASYNC_IDENTIFIERS`.
Fixes#593
I looked into this bug with @ambv and @carljm, and we reached the
conclusion was that it's not possible for the tokenizer to determine if
async/await is a keyword inside all possible generators without breaking
the grammar for older versions of Python.
Instead, we introduce a new tokenizer mode for Python 3.7+ that will
cause all async/await instances to get parsed as a reserved keyword,
which should fix async/await inside generators.
This is a new syntax added in python3.7, so black can't verify that reformatting will not change the ast unless black itself is run with 3.7. We'll need to change the error message black gives in this case. @ambv any ideas?
Fixes#125.
This support isn't *exactly* right per PEP 3131 as the regex engine is a bit
too limited for that and I didn't want to spend time on Other_ID_Start and
Other_ID_Continue unless they're actually needed.
Hopefully this doesn't slow it down too much.
