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A protocol can constrain an associated type to Self:
protocol P {
associatedtype A : Q where A.B == Self
}
protocol Q {
associatedtype B
}
And a class might conform to this protocol:
class C : P {
typealias A = D
}
class D : Q {
typealias B = C
}
The generic signature <Self where Self : P, Self : C> is built during
conformance checking. Since Self : C, we must have that Self.A == D;
since D.B == C, the requierement 'A.B == Self' in protocol P implies
that 'Self == C'. So the correct minimized signature here is
<Self where Self == C>.
This wasn't handled properly before, because of assumptions in
removeSelfDerived() and a couple of other places.
Fixes rdar://71677712, rdar://76155506, https://bugs.swift.org/browse/SR-10033,
https://bugs.swift.org/browse/SR-13884.
35 lines
1.1 KiB
Swift
35 lines
1.1 KiB
Swift
// RUN: %target-typecheck-verify-swift
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// RUN: %target-swift-frontend -emit-ir -debug-generic-signatures %s 2>&1 | %FileCheck %s
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public protocol P {
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associatedtype A : Q where A.B == Self
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}
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public protocol Q {
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associatedtype B
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}
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public class C : P {
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public typealias A = D
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}
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public class D : Q {
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public typealias B = C
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}
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// Both <T : P & C> and <T : C & P> minimize to <T where T == C>:
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// - T : P and T : C imply that T.A == C.A == D;
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// - T : P also implies that T.A.B == T, via A.B == Self in P;
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// - Since T.A == D, T.A.B == D.B, therefore Self == D.B.
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// - D.B is a typealias for C, so really Self == C.
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// CHECK-LABEL: Generic signature: <T where T == D.B>
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public func takesBoth1<T : P & C>(_: T) {}
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// expected-warning@-1 {{redundant conformance constraint 'T' : 'P'}}
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// expected-note@-2 {{conformance constraint 'T' : 'P' implied here}}
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// CHECK-LABEL: Generic signature: <U where U == D.B>
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public func takesBoth2<U : C & P>(_: U) {}
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// expected-warning@-1 {{redundant conformance constraint 'U' : 'P'}}
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// expected-note@-2 {{conformance constraint 'U' : 'P' implied here}}
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