Always enable "missing" conformances to Sendable.

Always build the conformances, and produce warnings/errors when they are
needed during type checking.

Author: DougGregor

include/swift/AST/Decl.h

@@ -3251,7 +3251,8 @@ class NominalTypeDecl : public GenericTypeDecl, public IterableDeclContext {
   ///
   /// This is used by deserialization of module files to report
   /// conformances.
-  void registerProtocolConformance(ProtocolConformance *conformance);
+  void registerProtocolConformance(ProtocolConformance *conformance,
+                                   bool synthesized = false);
 
   void setConformanceLoader(LazyMemberLoader *resolver, uint64_t contextData);
 

lib/AST/Module.cpp

@@ -996,8 +996,7 @@ static ProtocolConformanceRef getInvalidOrMissingConformance(
   // Introduce "missing" conformances to Sendable, so that type checking
   // (and even code generation) can continue.
   ASTContext &ctx = proto->getASTContext();
-  if (proto->isSpecificProtocol(KnownProtocolKind::Sendable) &&
-      ctx.LangOpts.WarnConcurrency) {
+  if (proto->isSpecificProtocol(KnownProtocolKind::Sendable)) {
     return ProtocolConformanceRef(
         ctx.getBuiltinConformance(
           type, proto, GenericSignature(), { },

lib/AST/ProtocolConformance.cpp

@@ -1320,9 +1320,9 @@ void NominalTypeDecl::getImplicitProtocols(
 }
 
 void NominalTypeDecl::registerProtocolConformance(
-       ProtocolConformance *conformance) {
+       ProtocolConformance *conformance, bool synthesized) {
   prepareConformanceTable();
-  ConformanceTable->registerProtocolConformance(conformance);
+  ConformanceTable->registerProtocolConformance(conformance, synthesized);
 }
 
 ArrayRef<ValueDecl *>

lib/Sema/TypeCheckConcurrency.cpp

@@ -3741,6 +3741,7 @@ NormalProtocolConformance *GetImplicitSendableRequest::evaluate(
     conformance->setSourceKindAndImplyingConformance(
         ConformanceEntryKind::Synthesized, nullptr);
 
+    nominal->registerProtocolConformance(conformance, /*synthesized=*/true);
     return conformance;
   };
 

test/Concurrency/concurrent_value_inference.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift -enable-library-evolution -disable-availability-checking
+// RUN: %target-typecheck-verify-swift -enable-library-evolution
 // REQUIRES: concurrency
 
 class C1 { }
@@ -27,7 +27,6 @@ struct GS2<T> {
 }
 
 func acceptCV<T: Sendable>(_: T) { }
-// expected-note@-1 6{{where 'T' =}}
 
 // Example that was triggering circular dependencies.
 struct Signature { }
@@ -86,6 +85,7 @@ struct HasFunctions {
   var cfp: @convention(c) () -> Void
 }
 
+@available(SwiftStdlib 5.5, *)
 @globalActor
 actor MyGlobalActor {
   static let shared = MyGlobalActor()
@@ -103,22 +103,22 @@ func testCV(
   fps: FrozenPublicStruct, fpe: FrozenPublicEnum,
   hf: HasFunctions
 ) {
-  acceptCV(c1) // expected-error{{'C1' conform to 'Sendable'}}
+  acceptCV(c1) // expected-warning{{type 'C1' does not conform to the 'Sendable' protocol}}
   acceptCV(c2)
   acceptCV(c3)
   acceptCV(c4)
   acceptCV(s1)
-  acceptCV(e1) // expected-error{{'E1' conform to 'Sendable'}}
+  acceptCV(e1) // expected-warning{{type 'E1' does not conform to the 'Sendable'}}
   acceptCV(e2)
   acceptCV(gs1)
-  acceptCV(gs2) // expected-error{{'GS2<Int>' conform to 'Sendable'}}
+  acceptCV(gs2) // expected-warning{{type 'GS2<Int>' does not conform to the 'Sendable' protocol}}
 
   // Not available due to recursive conformance dependencies.
-  acceptCV(bc) // expected-error{{global function 'acceptCV' requires that 'Bitcode' conform to 'Sendable'}}
+  acceptCV(bc) // expected-warning{{type 'Bitcode' does not conform to the 'Sendable' protocol}}
 
   // Not available due to "public".
-  acceptCV(ps) // expected-error{{global function 'acceptCV' requires that 'PublicStruct' conform to 'Sendable'}}
-  acceptCV(pe) // expected-error{{global function 'acceptCV' requires that 'PublicEnum' conform to 'Sendable'}}
+  acceptCV(ps) // expected-warning{{type 'PublicStruct' does not conform to the 'Sendable' protocol}}
+  acceptCV(pe) // expected-warning{{type 'PublicEnum' does not conform to the 'Sendable' protocol}}
 
   // Public is okay when also @frozen.
   acceptCV(fps)