Merge pull request #42538 from slavapestov/testcase-rdar92092635

Add test case for rdar://92092635

Author: slavapestov

lib/AST/RequirementMachine/RequirementLowering.cpp

@@ -340,7 +340,7 @@ static void desugarConformanceRequirement(Type subjectType, Type constraintType,
   }
 
   for (auto memberType : compositionType->getMembers()) {
-    if (memberType->isExistentialType())
+    if (memberType->isConstraintType())
       desugarConformanceRequirement(subjectType, memberType,
                                     loc, result, errors);
     else

test/Generics/redundant_protocol_composition.swift

@@ -0,0 +1,19 @@
+// RUN: %target-typecheck-verify-swift -requirement-machine-inferred-signatures=on
+
+// The GenericSignatureBuilder did not diagnose the first two.
+
+struct G1<T : BinaryInteger & FixedWidthInteger & UnsignedInteger & Codable> {}
+// expected-warning@-1 {{redundant conformance constraint 'T' : 'BinaryInteger'}}
+
+struct G2<T> where T : BinaryInteger & FixedWidthInteger & UnsignedInteger & Codable {}
+// expected-warning@-1 {{redundant conformance constraint 'T' : 'BinaryInteger'}}
+
+struct G3<T> where T : BinaryInteger, T : FixedWidthInteger, T : UnsignedInteger & Codable {}
+// expected-warning@-1 {{redundant conformance constraint 'T' : 'BinaryInteger'}}
+
+// FIXME: These should also diagnose, but do not due to overly-eager
+// canonicalization in ProtocolCompositionType::get().
+
+struct G1a<T : BinaryInteger & FixedWidthInteger & UnsignedInteger> {}
+struct G2a<T> where T : BinaryInteger & FixedWidthInteger & UnsignedInteger {}
+