Sema: Don't complain about implied Sendable conformance of imported type being retroactive

- Fixes rdar://145184871.

Author: slavapestov

lib/Sema/TypeCheckConcurrency.cpp

@@ -6935,13 +6935,16 @@ bool swift::checkSendableConformance(
     return false;
   }
 
+  // An implied conformance is generated when you state a conformance to
+  // a protocol P that inherits from Sendable.
+  bool wasImplied = (conformance->getSourceKind() ==
+                     ConformanceEntryKind::Implied);
+
   // Sendable can only be used in the same source file.
   auto conformanceDecl = conformanceDC->getAsDecl();
   SendableCheckContext checkContext(conformanceDC, check);
   DiagnosticBehavior behavior = checkContext.defaultDiagnosticBehavior();
-  if (conformance->getSourceKind() == ConformanceEntryKind::Implied &&
-      conformance->getProtocol()->isSpecificProtocol(
-          KnownProtocolKind::Sendable)) {
+  if (wasImplied) {
     if (auto optBehavior = checkContext.preconcurrencyBehavior(
             nominal, /*ignoreExplicitConformance=*/true))
       behavior = *optBehavior;
@@ -6950,12 +6953,14 @@ bool swift::checkSendableConformance(
   if (conformanceDC->getOutermostParentSourceFile() &&
       conformanceDC->getOutermostParentSourceFile() !=
       nominal->getOutermostParentSourceFile()) {
-    conformanceDecl->diagnose(diag::concurrent_value_outside_source_file,
-                              nominal)
-      .limitBehaviorUntilSwiftVersion(behavior, 6);
+    if (!(nominal->hasClangNode() && wasImplied)) {
+      conformanceDecl->diagnose(diag::concurrent_value_outside_source_file,
+                                nominal)
+        .limitBehaviorUntilSwiftVersion(behavior, 6);
 
-    if (behavior == DiagnosticBehavior::Unspecified)
-      return true;
+      if (behavior == DiagnosticBehavior::Unspecified)
+        return true;
+    }
   }
 
   if (classDecl && classDecl->getParentSourceFile()) {
@@ -6993,7 +6998,7 @@ bool swift::checkSendableConformance(
   // a Sendable conformance. The implied conformance is unconditional, so check
   // the storage for sendability as if the conformance was declared on the nominal,
   // and not some (possibly constrained) extension.
-  if (conformance->getSourceKind() == ConformanceEntryKind::Implied)
+  if (wasImplied)
     conformanceDC = nominal;
   return checkSendableInstanceStorage(nominal, conformanceDC, check);
 }

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -1844,6 +1844,18 @@ static void diagnoseRetroactiveConformances(
     bool inserted = protocols.insert(std::make_pair(
         proto, conformance->isRetroactive())).second;
     ASSERT(inserted);
+
+    if (proto->isSpecificProtocol(KnownProtocolKind::SendableMetatype)) {
+      protocolsWithRetroactiveAttr.insert(proto);
+    }
+
+    // Implied conformance to Sendable is a special case that should not be
+    // diagnosed. Pretend it's always @retroactive.
+    if (conformance->getSourceKind() == ConformanceEntryKind::Implied &&
+        proto->isSpecificProtocol(KnownProtocolKind::Sendable) &&
+        extendedNominalDecl->hasClangNode()) {
+      protocolsWithRetroactiveAttr.insert(proto);
+    }
   }
 
   for (const InheritedEntry &entry : ext->getInherited().getEntries()) {

test/Concurrency/implied_sendable_conformance_objc.swift

@@ -0,0 +1,15 @@
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-sil -o /dev/null -I %S/Inputs/custom-modules %s -verify -parse-as-library -swift-version 6
+
+// REQUIRES: objc_interop
+// REQUIRES: concurrency
+
+import Foundation
+
+extension CGRect: Sendable {}
+// expected-warning@-1 {{extension declares a conformance of imported type 'CGRect' to imported protocol 'Sendable'; this will not behave correctly if the owners of 'CoreGraphics' introduce this conformance in the future}}
+// expected-note@-2 {{add '@retroactive' to silence this warning}}
+// expected-error@-3 {{conformance to 'Sendable' must occur in the same source file as struct 'CGRect'; use '@unchecked Sendable' for retroactive conformance}}
+protocol P: Sendable {}
+
+extension CGPoint: P {}
+

test/Inputs/clang-importer-sdk/swift-modules/CoreFoundation.swift

@@ -3,7 +3,7 @@
 protocol _CFObject: Hashable {}
 
 #if CGFLOAT_IN_COREFOUNDATION
-public struct CGFloat {
+public struct CGFloat: @unchecked Sendable {
 #if _pointerBitWidth(_32)
   public typealias UnderlyingType = Float
 #elseif _pointerBitWidth(_64)

test/Inputs/clang-importer-sdk/swift-modules/CoreGraphics.swift

@@ -6,7 +6,7 @@ public func == (lhs: CGPoint, rhs: CGPoint) -> Bool {
 }
 
 #if !CGFLOAT_IN_COREFOUNDATION
-public struct CGFloat {
+public struct CGFloat: Sendable {
 #if _pointerBitWidth(_32)
   public typealias UnderlyingType = Float
 #elseif _pointerBitWidth(_64)