Errors with recursive type aliases: "JSON is declared to have type `TypeAlias` but is used as type `UnionType`"

[cjolowicz]

Pyre Bug

Bug description

This recursive type alias for JSON data does not work in pyre:

from typing import TypeAlias

JSON: TypeAlias = None | bool | int | float | str | list["JSON"] | dict[str, "JSON"]

Output:

ƛ Found 5 type errors!
jsontype.py:3:0 Incompatible variable type [9]: JSON is declared to have type `TypeAlias` but is used as type `UnionType`.
jsontype.py:3:18 Missing argument [20]: Call `bool.__ror__` expects argument in position 1.
jsontype.py:3:18 Missing argument [20]: Call `int.__ror__` expects argument in position 1.
jsontype.py:3:57 Incompatible parameter type [6]: In call `typing.GenericMeta.__getitem__`, for 1st positional argument, expected `Type[Variable[_T]]` but got `str`.
jsontype.py:3:72 Incompatible parameter type [6]: In call `typing.GenericMeta.__getitem__`, for 1st positional argument, expected `Tuple[Type[Variable[_KT]], Type[Variable[_VT]]]` but got `Tuple[Type[str], str]`.

Reproduction steps

https://pyre-check.org/play?input=%23%20pyre-strict%0Afrom%20typing%20import%20TypeAlias%0A%0AJSON%3A%20TypeAlias%20%3D%20None%20%7C%20bool%20%7C%20int%20%7C%20float%20%7C%20str%20%7C%20list%5B%22JSON%22%5D%20%7C%20dict%5Bstr%2C%20%22JSON%22%5D

Alternatively:

$ pipx install pyre-check  # 0.9.19
$ cat jsontype.py  # source as above
$ pyre --source-directory . check  # errors as above

Expected behavior

No errors

Logs

Please run your reproduction steps followed by pyre rage > pyre_rage.log, and upload the file here:

pyre_rage.log

Additional context

This is the recommended definition from python/typing#182 (comment)

The code type-checks in mypy and pytype.

Omitting the quotes makes the code pass in pyre, but results in NameError at runtime:

NameError: name 'JSON' is not defined

This NameError cannot be avoided with future annotations, because it doesn't occur in an annotation.

PEP 695 type aliases don't appear to be supported yet:

type JSON = None | bool | int | float | str | list[JSON] | dict[str, JSON]
# jsontype.py:1:6 Parsing failure [404]: invalid syntax

Omitting the TypeAlias annotation avoids the first of the errors, but not the remaining four (missing argument, incompatible parameter type).

[vthemelis]

Not being able to type recursive types seems like a big regression? I thought this used to be possible in pyre. I stumbled upon this today at work and I'm surprised not more people are asking for this.

Also, is PEP 695 going to be implemented in pyre?

[yangdanny97]

is PEP 695 going to be implemented in pyre?

Yes, it's in the works and should be ready by EOY

The other stuff I'll need to investigate, not sure if this is a regression or if we never supported it in the first place.