[red-knot] Narrowing for type(x) is C checks#14432
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Add type narrowing for `type(x) is C` conditions:
```py
if type(x) is A:
reveal_type(x) # revealed: A
else:
reveal_type(x) # revealed: A | B
```
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sharkdp
commented
Nov 18, 2024
| x = get_a_or_b() | ||
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| if type(x) == A: | ||
| reveal_type(x) # revealed: A | B |
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Both pyright and mypy are less strict here and infer A instead of A | B. This is unsound, as can be demonstrated by returning B() from get_a_or_b(), and observing that this branch is taken.
CodSpeed Performance ReportMerging #14432 will not alter performanceComparing Summary
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AlexWaygood
approved these changes
Nov 18, 2024
crates/red_knot_python_semantic/resources/mdtest/narrow/type.md
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AlexWaygood
reviewed
Nov 18, 2024
AlexWaygood
requested changes
Nov 18, 2024
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Ah, the performance regression is probably from removing this (now insufficient) check: if !left.is_name_expr() && comparators.iter().all(|c| !c.is_name_expr()) {
// If none of the comparators are name expressions,
// we have no symbol to narrow down the type of.
return None;
}I'll look into it. Edit: fixed now by introducing a similar check. |
AlexWaygood
approved these changes
Nov 18, 2024
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Summary
Add type narrowing for
type(x) is Cconditions (andelseclauses oftype(x) is not Cconditionals):closes: #14431, part of: #13694
Test Plan
New Markdown-based tests.