[Associated type inference] Allow _Default_Foo typealias guides for inference.
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@swift-ci please test |
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@swift-ci please test source compatibility |
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UPASS is the best failure :) |
Introduce an ugly hack where a typealias in a protocol extension that has the name `_Default_Foo` can be found by associated type inference for an associated type named `Foo`, respecting the constrains of the protocol extension in which that typealias resides.
…nly. Factor out the two places where we were introducing a “tentative type witness” function within associated type inference. Then, extend this checking to allow us to use type witnesses from the known conformance even when we’re looking into an inherited conformance. This improves our ability to perform substitutions on the inferred-but-not-yet-committed type witnesses.
Use the new `_Default_Foo` typealias trickery to define a conditional default type witness for the collection `Indices` associated type, so `Indices` becomes `CountableRange<Index>` when the `Index` type is `Strideable` with `Int` as its `Stride` type. This fixes the major regression with associated type inference for “minimal” random access collection types with `Int` index types, which has come up in a number of places. Note that I dropped the `@_implements` requirement because `_Default_Foo` is already off in its own namespace, and eventually we should get a real syntax for this. Fixes rdar://problem/35035322.
NFC to reduce the size of the “find solutions” function.
DougGregor
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Introduce an ugly hack where a typealias in a protocol extension that has the name
_Default_Foocan be found by associated type inference for an associated type namedFoo, respecting the constrains of the protocol extension in which that typealias resides.Use this new machinery to define a conditional default type witness for the collection
Indicesassociated type, soIndicesbecomesCountableRange<Index>when theIndextype isStrideablewithIntas itsStridetype.This fixes the major regression with associated type inference for “minimal” random access collection types with
Intindex types, which has come up in a number of places.Fixes rdar://problem/35035322 / SR-6620