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71e267d5b1
Under certain circumstances, introducing a concrete same-type or
superclass constraint can re-introduce conformance constraints
which were previously redundant.
For example, consider this code, which we correctly support today:
protocol P {
associatedtype T : Q
}
protocol Q {}
class SomeClass<U : Q> {}
struct Outer<T> where T : P {
func inner<U>(_: U) where T == SomeClass<U>, U : Q {}
}
The constraint 'T == SomeClass<U>' makes the outer constraint
`T : P' redundant, because SomeClass already conforms to P.
It also introduces an implied same-type constraint 'U == T.T'.
However, whereas 'T : P' together with 'U == T.T' make 'U : Q'
redundant, the introduction of the constraint 'T == SomeClass<U>'
removes 'T : P', so we re-introduce an explicit constraint 'U : Q'
in order to get a valid generic signature.
This code path did the right thing for constraints derived via
concrete same-type constraints, but it did not handle superclass
constraints.
As a result, this case was broken:
struct Outer<T> where T : P {
func inner<U>(_: U) where T : SomeClass<U>, U : Q {}
}
This is the same example as above, except T is related via a
superclass constraint to SomeClass<U>, instead of via a concrete
same-type constraint.
The subtlety here is that we must check if the superclass type
actually conforms to the requirement source's protocol, because it
is possible to have a superclass-constrained generic parameter
where some conformances are abstract. Eg, if SomeClass did not
conform to another protocol P2, we could write
func foo<T, U>(_: T, _: U) where T : SomeClass<U>, T : P2 {}
In this case, 'T : P2' is an abstract conformance on the type 'T'.
The common case where this would come up in real code is when you
have a class that conforms to a protocol with an associated type,
and one of the protocol requirements was fulfilled by a default in
a protocol extension, eg:
protocol P {
associatedtype T : Q
func foo()
}
extension P {
func foo() {}
}
class ConformsWithDefault<T : Q> : P {}
The above used to crash; now it will type-check correctly.
Fixes <rdar://problem/44736411>, <https://bugs.swift.org/browse/SR-8814>..
49 lines
2.1 KiB
Swift
49 lines
2.1 KiB
Swift
// RUN: %target-swift-emit-silgen %s | %FileCheck %s
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protocol P {
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associatedtype T : Q
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func foo()
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}
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extension P {
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func foo() {}
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}
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protocol Q {}
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class C<T : Q> : P {}
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protocol PP {
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associatedtype T : QQ
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func foo()
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}
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extension PP {
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func foo() {}
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}
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class QQ {}
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class CC<T : QQ> : PP {}
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// CHECK-LABEL: sil private [transparent] [thunk] [ossa] @$s42class_conforms_with_default_implementation1CCyqd__GAA1PA2aEP3fooyyFTW : $@convention(witness_method: P) <τ_0_0><τ_1_0 where τ_0_0 : C<τ_1_0>, τ_1_0 : Q> (@in_guaranteed τ_0_0) -> () {
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// CHECK: [[WITNESS:%.*]] = function_ref @$s42class_conforms_with_default_implementation1PPAAE3fooyyF : $@convention(method) <τ_0_0 where τ_0_0 : P> (@in_guaranteed τ_0_0) -> ()
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// CHECK: apply [[WITNESS]]<τ_0_0>(%0) : $@convention(method) <τ_0_0 where τ_0_0 : P> (@in_guaranteed τ_0_0) -> ()
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// CHECK: return
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// CHECK-LABEL: sil private [transparent] [thunk] [ossa] @$s42class_conforms_with_default_implementation2CCCyqd__GAA2PPA2aEP3fooyyFTW : $@convention(witness_method: PP) <τ_0_0><τ_1_0 where τ_0_0 : CC<τ_1_0>, τ_1_0 : QQ> (@in_guaranteed τ_0_0) -> () {
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// CHECK: [[WITNESS:%.*]] = function_ref @$s42class_conforms_with_default_implementation2PPPAAE3fooyyF : $@convention(method) <τ_0_0 where τ_0_0 : PP> (@in_guaranteed τ_0_0) -> ()
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// CHECK: apply [[WITNESS]]<τ_0_0>(%0) : $@convention(method) <τ_0_0 where τ_0_0 : PP> (@in_guaranteed τ_0_0) -> ()
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// CHECK: return
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// CHECK-LABEL: sil_witness_table hidden <T where T : Q> C<T>: P module class_conforms_with_default_implementation {
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// CHECK-NEXT: associated_type_protocol (T: Q): dependent
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// CHECK-NEXT: associated_type T: T
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// CHECK-NEXT: method #P.foo: <Self where Self : P> (Self) -> () -> () : @$s42class_conforms_with_default_implementation1CCyqd__GAA1PA2aEP3fooyyFTW
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// CHECK-NEXT: }
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// CHECK-LABEL: sil_witness_table hidden <T where T : QQ> CC<T>: PP module class_conforms_with_default_implementation {
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// CHECK-NEXT: associated_type T: T
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// CHECK-NEXT: method #PP.foo: <Self where Self : PP> (Self) -> () -> () : @$s42class_conforms_with_default_implementation2CCCyqd__GAA2PPA2aEP3fooyyFTW
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// CHECK-NEXT: }
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