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[red-knot] 'is_equivalent_to' is an equivalence relation (#15488)

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## Summary

Adds two additional tests for `is_equivalent_to` so that we cover all
properties of an [equivalence relation].

## Test Plan

```
while cargo test --release -p red_knot_python_semantic -- --ignored types::property_tests::stable; do :; done
```

[equivalence relation]:
https://en.wikipedia.org/wiki/Equivalence_relation
This commit is contained in:
David Peter 2025-01-15 09:25:46 +01:00 • committed by GitHub
parent 96c2d0996d
commit d4862844f1
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1 changed files with 15 additions and 2 deletions
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17
crates/red_knot_python_semantic/src/types/property_tests.rs
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@ -234,12 +234,25 @@ mod stable {
use super::union;
use crate::types::{KnownClass, Type};
// `T` is equivalent to itself.
// Reflexivity: `T` is equivalent to itself.
type_property_test!(
equivalent_to_is_reflexive, db,
forall types t. t.is_fully_static(db) => t.is_equivalent_to(db, t)
);
// Symmetry: If `S` is equivalent to `T`, then `T` must be equivalent to `S`.
// Note that this (trivially) holds true for gradual types as well.
type_property_test!(
equivalent_to_is_symmetric, db,
forall types s, t. s.is_equivalent_to(db, t) => t.is_equivalent_to(db, s)
);
// Transitivity: If `S` is equivalent to `T` and `T` is equivalent to `U`, then `S` must be equivalent to `U`.
type_property_test!(
equivalent_to_is_transitive, db,
forall types s, t, u. s.is_equivalent_to(db, t) && t.is_equivalent_to(db, u) => s.is_equivalent_to(db, u)
);
// A fully static type `T` is a subtype of itself.
type_property_test!(
subtype_of_is_reflexive, db,
@ -365,7 +378,7 @@ mod flaky {
// For two fully static types, their intersection must be a subtype of each type in the pair.
type_property_test!(
all_fully_static_type_pairs_are_supertypes_of_their_union, db,
all_fully_static_type_pairs_are_supertypes_of_their_intersection, db,
forall types s, t.
s.is_fully_static(db) && t.is_fully_static(db)
=> intersection(db, s, t).is_subtype_of(db, s) && intersection(db, s, t).is_subtype_of(db, t)