Add a test case from a bug report in a forum post

https://forums.swift.org/t/wrong-redundant-conformance-constraint-warning/56207

Author: slavapestov

test/Generics/interdependent_protocol_conformance_example_1.swift

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+// RUN: %target-typecheck-verify-swift %s -requirement-machine-protocol-signatures=on
+// RUN: %target-swift-frontend -typecheck %s -debug-generic-signatures -requirement-machine-protocol-signatures=on 2>&1 | %FileCheck %s
+
+// The GenericSignatureBuilder was unable to derive the redundant conformance requirement 'B: P4'
+// in protocol P1.
+//
+// This version includes the requirement; see interdependent_protocol_conformance_example_2 for
+// the other case.
+
+// CHECK-LABEL: .P1@
+// CHECK-NEXT: Requirement signature: <Self where Self.[P1]A : P2, Self.[P1]B == Self.[P1]A.[P2]B>
+protocol P1 {
+  associatedtype A: P2 where Self.A.B == Self.B
+  associatedtype B: P4
+  // expected-warning@-1 {{redundant conformance constraint 'Self.B' : 'P4'}}
+}
+
+// CHECK-LABEL: .P2@
+// CHECK-NEXT: Requirement signature: <Self where Self.[P2]B == Self.[P2]C.[P3]B, Self.[P2]C : P3>
+protocol P2 {
+  associatedtype B
+  associatedtype C: P3 where Self.C.B == Self.B
+}
+
+// CHECK-LABEL: .P3@
+// CHECK-NEXT: Requirement signature: <Self where Self.[P3]B : P4>
+protocol P3 {
+  associatedtype B: P4
+}
+
+// CHECK-LABEL: .P4@
+// CHECK-NEXT: Requirement signature: <Self where Self == Self.[P4]A.[P2]B, Self.[P4]A : P2>
+protocol P4 {
+  associatedtype A: P2 where Self.A.B == Self
+}
+
+func takesP4<T : P4>(_: T.Type) {}
+
+func testP1<T : P1>(_: T) {
+  takesP4(T.B.self)
+}

test/Generics/interdependent_protocol_conformance_example_2.swift

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+// RUN: %target-typecheck-verify-swift %s -requirement-machine-protocol-signatures=on
+// RUN: %target-swift-frontend -typecheck %s -debug-generic-signatures -requirement-machine-protocol-signatures=on 2>&1 | %FileCheck %s
+
+// The GenericSignatureBuilder was unable to derive the redundant conformance requirement 'B: P4'
+// in protocol P1.
+//
+// This version omits the requirement; see interdependent_protocol_conformance_example_1 for
+// the other case.
+
+// CHECK-LABEL: .P1@
+// CHECK-NEXT: Requirement signature: <Self where Self.[P1]A : P2, Self.[P1]B == Self.[P1]A.[P2]B>
+protocol P1 {
+  associatedtype A: P2 where Self.A.B == Self.B
+  associatedtype B
+}
+
+// CHECK-LABEL: .P2@
+// CHECK-NEXT: Requirement signature: <Self where Self.[P2]B == Self.[P2]C.[P3]B, Self.[P2]C : P3>
+protocol P2 {
+  associatedtype B
+  associatedtype C: P3 where Self.C.B == Self.B
+}
+
+// CHECK-LABEL: .P3@
+// CHECK-NEXT: Requirement signature: <Self where Self.[P3]B : P4>
+protocol P3 {
+  associatedtype B: P4
+}
+
+// CHECK-LABEL: .P4@
+// CHECK-NEXT: Requirement signature: <Self where Self == Self.[P4]A.[P2]B, Self.[P4]A : P2>
+protocol P4 {
+  associatedtype A: P2 where Self.A.B == Self
+}
+
+func takesP4<T : P4>(_: T.Type) {}
+
+func testP1<T : P1>(_: T) {
+  takesP4(T.B.self)
+}