[Concurrency] Fix SendableMetatype conformance failures to behave like Sendable ones

No warnings with minimal checking, warnings with `strict-concurrency=complete` and
if declaration is `@preconcurrency` until next major swift version.

Resolves: rdar://151911135
Resolves: swiftlang#81739

Author: xedin

include/swift/AST/DiagnosticsSema.def

@@ -2794,9 +2794,9 @@ NOTE(non_sendable_nominal,none,
 NOTE(add_nominal_sendable_conformance,none,
      "consider making %kind0 conform to the 'Sendable' protocol",
      (const ValueDecl *))
-NOTE(add_generic_parameter_sendable_conformance,none,
-     "consider making generic parameter %0 conform to the 'Sendable' protocol",
-     (Type))
+NOTE(add_generic_parameter_conformance,none,
+     "consider making generic parameter %0 conform to the %1 protocol",
+     (Type, ProtocolDecl *))
 WARNING(add_predates_concurrency_import,none,
      "add '@preconcurrency' to %select{suppress|treat}0 "
      "'Sendable'-related %select{warnings|errors}0 from module %1"
@@ -5941,6 +5941,8 @@ ERROR(concurrent_value_inherit,none,
       (bool, DeclName))
 ERROR(non_sendable_type,none,
       "type %0 does not conform to the 'Sendable' protocol", (Type))
+GROUPED_ERROR(non_sendable_metatype_type,SendableMetatypes,none,
+      "type %0 does not conform to the 'SendableMetatype' protocol", (Type))
 ERROR(sendable_raw_storage,none,
       "struct %0 with '@_rawLayout' does not conform to the 'Sendable' "
       "protocol", (DeclName))

lib/AST/ConformanceLookup.cpp

@@ -173,6 +173,10 @@ static bool shouldCreateMissingConformances(Type type, ProtocolDecl *proto) {
     return true;
   }
 
+  // SendableMetatype behaves similarly to Sendable.
+  if (proto->isSpecificProtocol(KnownProtocolKind::SendableMetatype))
+    return true;
+
   return false;
 }
 

lib/Sema/TypeCheckAvailability.cpp

@@ -3320,8 +3320,15 @@ void swift::diagnoseTypeAvailability(const TypeRepr *TR, Type T, SourceLoc loc,
 static void diagnoseMissingConformance(
     SourceLoc loc, Type type, ProtocolDecl *proto, const DeclContext *fromDC,
     bool preconcurrency) {
-  assert(proto->isSpecificProtocol(KnownProtocolKind::Sendable));
-  diagnoseMissingSendableConformance(loc, type, fromDC, preconcurrency);
+  assert(proto->isSpecificProtocol(KnownProtocolKind::Sendable) ||
+         proto->isSpecificProtocol(KnownProtocolKind::SendableMetatype));
+
+  if (proto->isSpecificProtocol(KnownProtocolKind::Sendable))
+    diagnoseMissingSendableConformance(loc, type, fromDC, preconcurrency);
+
+  if (proto->isSpecificProtocol(KnownProtocolKind::SendableMetatype))
+    diagnoseMissingSendableMetatypeConformance(loc, type, fromDC,
+                                               preconcurrency);
 }
 
 bool

lib/Sema/TypeCheckConcurrency.cpp

@@ -764,18 +764,30 @@ static void addSendableFixIt(
   }
 }
 
-/// Add Fix-It text for the given generic param declaration type to adopt
-/// Sendable.
-static void addSendableFixIt(const GenericTypeParamDecl *genericArgument,
-                             InFlightDiagnostic &diag) {
+static void addProtocolFixIt(const GenericTypeParamDecl *genericArgument,
+                             InFlightDiagnostic &diag, StringRef protocolName) {
   if (genericArgument->getInherited().empty()) {
     auto fixItLoc = genericArgument->getLoc();
-    diag.fixItInsertAfter(fixItLoc, ": Sendable");
+    diag.fixItInsertAfter(fixItLoc, llvm::Twine(": ", protocolName).str());
   } else {
     auto fixItLoc = genericArgument->getInherited().getEndLoc();
-    diag.fixItInsertAfter(fixItLoc, " & Sendable");
+    diag.fixItInsertAfter(fixItLoc, llvm::Twine(" & ", protocolName).str());
   }
 }
+/// Add Fix-It text for the given generic param declaration type to adopt
+/// Sendable.
+static void addSendableFixIt(const GenericTypeParamDecl *genericArgument,
+                             InFlightDiagnostic &diag) {
+  addProtocolFixIt(genericArgument, diag,
+                   getProtocolName(KnownProtocolKind::Sendable));
+}
+
+static void
+addSendableMetatypeFixIt(const GenericTypeParamDecl *genericArgument,
+                         InFlightDiagnostic &diag) {
+  addProtocolFixIt(genericArgument, diag,
+                   getProtocolName(KnownProtocolKind::SendableMetatype));
+}
 
 static bool shouldDiagnoseExistingDataRaces(const DeclContext *dc) {
   return contextRequiresStrictConcurrencyChecking(dc, [](const AbstractClosureExpr *) {
@@ -1025,7 +1037,8 @@ static bool diagnoseSingleNonSendableType(
         if (genericParamTypeDecl &&
             genericParamTypeDecl->getModuleContext() == module) {
           auto diag = genericParamTypeDecl->diagnose(
-              diag::add_generic_parameter_sendable_conformance, type);
+              diag::add_generic_parameter_conformance, type,
+              ctx.getProtocol(KnownProtocolKind::Sendable));
           addSendableFixIt(genericParamTypeDecl, diag);
         }
       }
@@ -1242,6 +1255,32 @@ void swift::diagnoseMissingSendableConformance(
       loc, diag::non_sendable_type);
 }
 
+void swift::diagnoseMissingSendableMetatypeConformance(
+    SourceLoc loc, Type type, const DeclContext *fromDC, bool preconcurrency) {
+  SendableCheckContext sendableContext(fromDC, preconcurrency);
+  DiagnosticBehavior behavior =
+      sendableContext.implicitSendableDiagnosticBehavior();
+
+  auto &ctx = type->getASTContext();
+  ctx.Diags.diagnose(loc, diag::non_sendable_metatype_type, type)
+      .limitBehaviorWithPreconcurrency(behavior, preconcurrency);
+
+  if (auto genericArchetype = type->getAs<ArchetypeType>()) {
+    auto interfaceType = genericArchetype->getInterfaceType();
+    if (auto genericParamType = interfaceType->getAs<GenericTypeParamType>()) {
+      auto module = fromDC->getParentModule();
+      auto *genericParamTypeDecl = genericParamType->getDecl();
+      if (genericParamTypeDecl &&
+          genericParamTypeDecl->getModuleContext() == module) {
+        auto diag = genericParamTypeDecl->diagnose(
+            diag::add_generic_parameter_conformance, type,
+            ctx.getProtocol(KnownProtocolKind::SendableMetatype));
+        addSendableMetatypeFixIt(genericParamTypeDecl, diag);
+      }
+    }
+  }
+}
+
 namespace {
 /// Infer Sendable from the instance storage of the given nominal type.
 /// \returns \c std::nullopt if there is no way to make the type \c Sendable,

lib/Sema/TypeCheckConcurrency.h

@@ -327,6 +327,11 @@ bool diagnoseNonSendableTypesInReference(
 void diagnoseMissingSendableConformance(
     SourceLoc loc, Type type, const DeclContext *fromDC, bool preconcurrency);
 
+/// Produce a diagnostic for a missing conformance to SendableMetatype
+void diagnoseMissingSendableMetatypeConformance(SourceLoc loc, Type type,
+                                                const DeclContext *fromDC,
+                                                bool preconcurrency);
+
 /// If the given nominal type is public and does not explicitly
 /// state whether it conforms to Sendable, provide a diagnostic.
 void diagnoseMissingExplicitSendable(NominalTypeDecl *nominal);

test/Concurrency/predates_concurrency.swift

@@ -357,3 +357,16 @@ do {
     }
   }
 }
+
+func testSendableMetatypeDowngrades() {
+  @preconcurrency
+  func acceptsSendableMetatype<T: SendableMetatype>(_: T.Type) {}
+  func acceptsSendableMetatypeStrict<T: SendableMetatype>(_: T.Type) {}
+
+  func test<T>(t: T.Type) { // expected-complete-tns-note 2 {{consider making generic parameter 'T' conform to the 'SendableMetatype' protocol}} {{14-14=: SendableMetatype}}
+    acceptsSendableMetatype(t)
+    // expected-complete-tns-warning@-1 {{type 'T' does not conform to the 'SendableMetatype' protocol}}
+    acceptsSendableMetatypeStrict(t)
+    // expected-complete-tns-warning@-1 {{type 'T' does not conform to the 'SendableMetatype' protocol}}
+  }
+}

test/Concurrency/predates_concurrency_swift6.swift

@@ -323,3 +323,18 @@ do {
     case test(NS) // expected-warning {{associated value 'test' of 'Sendable'-conforming enum 'E' has non-Sendable type 'NS'}}
   }
 }
+
+func testSendableMetatypeDowngrades() {
+  @preconcurrency
+  func acceptsSendableMetatype<T: SendableMetatype>(_: T.Type) {}
+  func acceptsSendableMetatypeStrict<T: SendableMetatype>(_: T.Type) {}
+
+  func testWarning<T>(t: T.Type) { // expected-note 2 {{consider making generic parameter 'T' conform to the 'SendableMetatype' protocol}} {{21-21=: SendableMetatype}}
+    acceptsSendableMetatype(t) // expected-warning {{type 'T' does not conform to the 'SendableMetatype' protocol}}
+    acceptsSendableMetatypeStrict(t) // expected-error {{type 'T' does not conform to the 'SendableMetatype' protocol}}
+  }
+
+  func testOK<T: P>(t: T.Type) {
+    acceptsSendableMetatype(t) // Ok (because P is `Sendable`
+  }
+}

test/Concurrency/sendable_metatype.swift

@@ -83,3 +83,18 @@ nonisolated func passMetaSmuggledAnyFromExistential(_ pqT: (P & Q).Type) {
     acceptMeta(x) // expected-note{{closure captures 'x' which is accessible to code in the current task}}
   }
 }
+
+
+func testSendableMetatypeDowngrades() {
+  @preconcurrency
+  func acceptsSendableMetatype<T: SendableMetatype>(_: T.Type) {
+  }
+
+  func testWarning<T>(t: T.Type) { // expected-note {{consider making generic parameter 'T' conform to the 'SendableMetatype' protocol}} {{21-21=: SendableMetatype}}
+    acceptsSendableMetatype(t) // expected-warning {{type 'T' does not conform to the 'SendableMetatype' protocol}}
+  }
+
+  func testWarning<T: P>(t: T.Type) { // expected-note {{consider making generic parameter 'T' conform to the 'SendableMetatype' protocol}} {{24-24= & SendableMetatype}}
+    acceptsSendableMetatype(t) // expected-warning {{type 'T' does not conform to the 'SendableMetatype' protocol}}
+  }
+}