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## Summary
@sharkdp and I realised in our 1:1 this morning that our control flow
for `assert` statements isn't quite accurate at the moment. Namely, for
something like this:
```py
def _(x: int | None):
assert x is None, reveal_type(x)
```
we currently reveal `None` for `x` here, but this is incorrect. In
actual fact, the `msg` expression of an `assert` statement (the
expression after the comma) will only be evaluated if the test (`x is
None`) evaluates to `False`. As such, we should be adding a constraint
of `~None` to `x` in the `msg` expression, which should simplify the
inferred type of `x` to `int` in that context (`(int | None) & ~None` ->
`int`).
## Test Plan
Mdtests added.
---------
Co-authored-by: David Peter <mail@david-peter.de>
Markdown files within the mdtest/ subdirectory are tests of type inference and type checking;
executed by the tests/mdtest.rs integration test.
See crates/red_knot_test/README.md for documentation of this test format.