Odd behavior of inference on generic types?

[dillydill123]

Describe the Bug

from typing import reveal_type

class Box[T]:
    value: T

def f() -> Box[int]:
    x = Box()
    reveal_type(x)
    return x

def g() -> list[int]:
    # Type inferred as list[Unknown]
    x = list()  # Note: Using [] will raise 'implicit-any-empty-container'
    reveal_type(x)
    return x

def h() -> list[int]:
    # Type inferred as list[int] without reveal_type
    x = list()
    return x

pyrefly produces no errors, but reveals x as Box[Unknown]. To me, this feels off, similar to implicit-any-type-argument but not quite, since we are returning Box[Unknown] on declared type Box[int]. Possibly related, adding reveal_type changes what the sandbox and pyrefly infers:

Box[Unknown]

Becomes Box[int] after commenting out reveal_type.

Without reveal_type, the inferred type is Box[int]. Is this behavior intended? Inferring Box[int] from the return type alone (with no constraining use to go off of) seems a little loose but this is a extraordinary and unlikely example I suppose.

As a comparison, mypy --strict will report [var-annotated]:

test.py:7: error: Need type annotation for "x"  [var-annotated]
test.py:8: note: Revealed type is "test.Box[Any]"
test.py:12: error: Need type annotation for "x" (hint: "x: list[<type>] = ...")  [var-annotated]
test.py:13: note: Revealed type is "list[Any]"
Found 2 errors in 1 file (checked 1 source file)

Apologies if I've misunderstood something about this. Thanks for any explanation you can give.

Sandbox Link

https://pyrefly.org/sandbox/?project=N4IgZglgNgpgziAXKOBDAdgEwEYHsAeAdAA4CeS4ATrgLYAEALqcROgOZ0Q3G6UN2UYANxiooAfSbEYAHXRyAxlFRw4dAEIEA2gBUAuojl1jdIWICuMRHR1y5mGGDpgAFAEo6AWgB8G7awYDIxN8OgBeP3x3YONBETFJZhgXfDcYgRgGc0p0Onw7LEc6NncvXygIOAYtAKDckwBiGyTOdDAYSkFMOhU6CqqtAFV0AGt0XAB3dD100Ij%2BhlK6JoA5XAYrOkG4Vg4tPToJ6CgBVEqYOgByLmIKhQgGTwxSTxhuJk8FXHQGM-QOy7pOKiCRSZKpIGZbK5fLyQpOAAWpR8fUq1VqhnqxiaOharHanRg3V6CxqPwORwYCNw5n4wISYNm4VRVWiWIyWRyeRAABoQGRBGAoKRCAxaFAKE0AAqkQXCuhoLB4UJfNoQNjZVAMCDfQhyJoAZRgFwRDAYxDgiAA9FaBY5hYReGwrTB0FbMLgFHArarIBrKFqdW7nLwemZoKhsLA6L71Zrtd86LhiAn0HA9egyFTvp4RJQdomIjIQABmQgARgATMW5MRBHBMszi1VKBAFAxiyAAL581DtiAiABi0BgFEVOAIJHIXaAA

(Only applicable for extension issues) IDE Information

No response