Merge pull request #75425 from hborla/redundant-copyable

[Conformance] Always downgrade redundant conformances to marker protocols to a warning.

Author: hborla

lib/Sema/TypeCheckProtocol.cpp

@@ -6276,7 +6276,7 @@ void TypeChecker::checkConformancesInContext(IterableDeclContext *idc) {
     }
 
     if ((existingModule != dc->getParentModule() && conformanceInOrigModule) ||
-        isSendable) {
+        diag.Protocol->isMarkerProtocol()) {
       // Warn about the conformance.
       if (isSendable && SendableConformance &&
           isa<InheritedProtocolConformance>(SendableConformance)) {

test/Parse/inverses.swift

@@ -140,7 +140,7 @@ struct Burrito<Filling: ~Copyable>: ~Copyable {}
 extension Burrito: Alias {} // expected-error {{conformance to 'Copyable' must be declared in a separate extension}}
 // expected-note@-1 {{'Burrito<Filling>' declares conformance to protocol 'Copyable' here}}
 
-extension Burrito: Copyable & Edible & P {} // expected-error {{redundant conformance of 'Burrito<Filling>' to protocol 'Copyable'}}
+extension Burrito: Copyable & Edible & P {} // expected-warning {{redundant conformance of 'Burrito<Filling>' to protocol 'Copyable'}}
 
 struct Blah<T: ~Copyable>: ~Copyable {}
 extension Blah: P, Q, Copyable, R {} // expected-error {{generic struct 'Blah' required to be 'Copyable' but is marked with '~Copyable'}}

test/decl/protocol/conforms/redundant_conformance.swift

@@ -86,3 +86,10 @@ class Class3 {
 class SomeMockClass: Class3.ProviderThree { // okay
   var someInt: Int = 5
 }
+
+
+class ImplicitCopyable {}
+
+class InheritImplicitCopyable: ImplicitCopyable, Copyable {}
+// expected-warning@-1 {{redundant conformance of 'InheritImplicitCopyable' to protocol 'Copyable'}}
+// expected-note@-2 {{'InheritImplicitCopyable' inherits conformance to protocol 'Copyable' from superclass here}}