NCGenerics: conformances can depend on Copyable

Author: kavon

lib/Sema/TypeCheckProtocol.cpp

@@ -2210,6 +2210,13 @@ static bool hasAdditionalSemanticChecks(ProtocolDecl *proto) {
   return proto->isSpecificProtocol(KnownProtocolKind::Sendable);
 }
 
+/// Determine whether a conformance to this protocol can be determined at
+/// runtime for an arbitrary type.
+static bool hasRuntimeConformanceInfo(ProtocolDecl *proto) {
+  return !proto->isMarkerProtocol()
+      || proto->isSpecificProtocol(KnownProtocolKind::Copyable);
+}
+
 static void ensureRequirementsAreSatisfied(ASTContext &ctx,
                                            NormalProtocolConformance *conformance);
 
@@ -2354,11 +2361,11 @@ checkIndividualConformance(NormalProtocolConformance *conformance) {
 
     // If the protocol to which we are conditionally conforming is not a marker
     // protocol, the conditional requirements must not involve conformance to a
-    // marker protocol. We cannot evaluate such a conformance at runtime.
+    // protocol that cannot be evaluated at runtime, like most marker protocols.
     if (!Proto->isMarkerProtocol()) {
       for (const auto &req : conditionalReqs) {
         if (req.getKind() == RequirementKind::Conformance &&
-            req.getProtocolDecl()->isMarkerProtocol()) {
+            !hasRuntimeConformanceInfo(req.getProtocolDecl())) {
           Context.Diags.diagnose(
             ComplainLoc, diag::marker_protocol_conditional_conformance,
             Proto->getName(), req.getFirstType(),

test/Generics/inverse_generics.swift

@@ -462,3 +462,20 @@ func checkExistentials() {
     let _: any Copyable & ~Copyable = 1 // expected-error {{composition cannot contain '~Copyable' when another member requires 'Copyable'}}
     let _: any Escapable & ~Escapable = 1 // expected-error {{composition cannot contain '~Escapable' when another member requires 'Escapable'}}
 }
+
+// Conformances can be conditional on whether a generic parameter is Copyable
+protocol Arbitrary {}
+protocol AnotherOne {}
+struct UnethicalPointer<Pointee: ~Copyable> {}
+extension UnethicalPointer: Arbitrary {}
+extension UnethicalPointer: AnotherOne where Pointee: Copyable {}
+
+struct StillIllegal1<Pointee: ~Escapable> {}
+extension StillIllegal1: Arbitrary {}
+// expected-error@-1 {{conditional conformance to non-marker protocol 'Arbitrary' cannot depend on conformance of 'Pointee' to marker protocol 'Escapable'}}
+extension StillIllegal1: AnotherOne where Pointee: Escapable {}
+// expected-error@-1 {{conditional conformance to non-marker protocol 'AnotherOne' cannot depend on conformance of 'Pointee' to marker protocol 'Escapable'}}
+
+struct SillIllegal2<Pointee> {}
+extension SillIllegal2: Arbitrary where Pointee: Sendable {}
+// expected-error@-1 {{conditional conformance to non-marker protocol 'Arbitrary' cannot depend on conformance of 'Pointee' to marker protocol 'Sendable'}}