[5.0] [Type checker] Allow extensions of typealiases naming generic specializations #21332
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…izations.
When a (non-generic) typealias refers to a specialization of a generic
type, e.g.
```swift
typealias simd_float3 = SIMD3<Float>
```
treat an extension of the typealias as an extension of the underlying
type with same-type constraints between the generic parameters and the
specific arguments, e.g.,
```swift
extension simd_float3 { }
```
is treated as
```swift
extension SIMD3 where Scalar == Float { }
```
This addresses a source-compatibility problem with SE-0229, where
existing types such as simd3_float (which were separate structs)
became specializations of a generic SIMD type.
Fixes rdar://problem/46604664 and rdar://problem/46604370.
(cherry picked from commit b88a875)
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AnnaZaks
approved these changes
Dec 15, 2018
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When a (non-generic) typealias refers to a specialization of a generic
type, e.g.
treat an extension of the typealias as an extension of the underlying
type with same-type constraints between the generic parameters and the
specific arguments, e.g.,
is treated as
This addresses a source-compatibility problem with SE-0229, where
existing types such as simd3_float (which were separate structs)
became specializations of a generic SIMD type.
Fixes rdar://problem/46604664 and rdar://problem/46604370.