Pyrefly does not eliminate conditional expression branches based on previous narrowing

[yangdanny97]

Describe the Bug

def f(x: int | None) -> None:
    if x is not None:
        y = 1 if x is not None else None # since we guard that x is not None, we could prune away the `else None` case in the ternary
        assert_type(y, int)

Python: 3.12

Sandbox Link

https://pyrefly.org/sandbox/?project=N4IgZglgNgpgziAXKOBDAdgEwEYHsAeAdAA4CeSImMYABGABT6I0ToAuNAPjQHK7owAlDQC0APl78YiADroaClrXws4NdLg58Bs%2BYv2kaAXhoBGJTRUQ1GrVJowocGJIFz9%2B1HGcAnNgH02UmIYelIAGhZ2QRBwkDIfaihSQjZcAFsoCgBiGgAFUkSwZJo0LDwVAGN%2BSABzAFcfVDYIfkI5XIBlGBcACzY2YjhEAHoRhKSU3B9akZh0EcxcSrgR6vQ6xubWhbppmlQAN1RoVGxYGnXNppb%2BGlxiW-Q4dvQyNl7%2BEUOYHzgd4w0GQgADMhFMACZgXIANq-HzTOAAXTk9XQEHSxGmbBgmBEmAgiUqLR%2BgIA5BBahpEmS5LYRIkAI71Qm4kQAaxgpBEqEqlXgahMZIA7qgfOhaegQABfOK8kkwABi0BgFDKOAIJHI0qAA

(Only applicable for extension issues) IDE Information

No response

[yangdanny97]

This looks similar to issues we've had where pyrefly doesn't eliminate cases in boolean expressions, which is a limitation of our control flow modeling

[yangdanny97]

Mypy behaves as expected in the example, but pyright emits "Condition will always evaluate to True since the types "int" and "None" have no overlap" + infers the same type as Pyrefly (Literal[1] | None)