* Allow walrus in slices
See https://github.com/python/cpython/pull/23317
Raised in #930.
* Fix parsing of nested f-string specifiers
For an expression like `f"{one:{two:}{three}}"`, `three` is not in an f-string spec, and should be tokenized accordingly.
This PR fixes the `format_spec_count` bookkeeping in the tokenizer, so it properly decrements it when a closing `}` is encountered but only if the `}` closes a format_spec.
Reported in #930.
* Fix tokenizing `0else`
This is an obscure one.
`_ if 0else _` failed to parse with some very weird errors. It turns out that the tokenizer tries to parse `0else` as a single number, but when it encounters `l` it realizes it can't be a single number and it backtracks.
Unfortunately the backtracking logic was broken, and it failed to correctly backtrack one of the offsets used for whitespace parsing (the byte offset since the start of the line). This caused whitespace nodes to refer to incorrect parts of the input text, eventually resulting in the above behavior.
This PR fixes the bookkeeping when the tokenizer backtracks.
Reported in #930.
* Allow no whitespace between lambda keyword and params in certain cases
Python accepts code where `lambda` follows a `*`, so this PR relaxes validation rules for Lambdas.
Raised in #930.
* Allow any expression in comprehensions' evaluated expression
This PR relaxes the accepted types for the `elt` field in `ListComp`, `SetComp`, and `GenExp`, as well as the `key` and `value` fields in `DictComp`.
Fixes#500.
* Allow no space around an ifexp in certain cases
For example in `_ if _ else""if _ else _`.
Raised in #930. Also fixes#854.
* Allow no spaces after `as` in a contextmanager in certain cases
Like in `with foo()as():pass`
Raised in #930.
* Allow no spaces around walrus in certain cases
Like in `[_:=''for _ in _]`
Raised in #930.
* Allow no whitespace after lambda body in certain cases
Like in `[lambda:()for _ in _]`
Reported in #930.
While these classes are used by the codegen implementation, conceptually
they're part of `libcst.metadata`, so we should export them from
`libcst.metadata` instead of the top-level `libcst` package.
This was a pain, because apparently we can't refer to
"static_analysis.libcst" as a module before its finished executing, due
to https://bugs.python.org/issue25294. To combat this, I had to change
to direct importing inside parser, which was a bit of a pain due to the
number of nodes used. But, it works.
