[Property delegates] Fix textual interfaces for properties with delegates

Don’t synthesize a missing setter for a property that has an attached
delegate and is in a .swiftinterface file.

Author: DougGregor

lib/Sema/CodeSynthesis.cpp

@@ -1771,11 +1771,14 @@ static void maybeAddAccessorsForPropertyDelegate(VarDecl *var,
   auto valueVar = var->getAttachedPropertyDelegateTypeInfo().valueVar;
   assert(valueVar && "Cannot fail when the backing var is valid");
 
+  auto parentSF = var->getDeclContext()->getParentSourceFile();
   bool delegateSetterIsUsable =
     var->getSetter() ||
-    (!var->isLet() &&
-       valueVar->isSettable(nullptr) &&
-       valueVar->isSetterAccessibleFrom(var->getInnermostDeclContext()));
+    (parentSF &&
+     parentSF->Kind != SourceFileKind::Interface &&
+     !var->isLet() &&
+     valueVar->isSettable(nullptr) &&
+     valueVar->isSetterAccessibleFrom(var->getInnermostDeclContext()));
 
   if (!var->getGetter()) {
     addGetterToStorage(var, ctx);

test/ParseableInterface/property-delegates.swift

@@ -0,0 +1,45 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend -typecheck -swift-version 5 -module-name TestResilient -emit-parseable-module-interface-path %t/TestResilient.swiftinterface -enable-library-evolution %s
+// RUN: %FileCheck %s < %t/TestResilient.swiftinterface --check-prefix CHECK --check-prefix RESILIENT
+
+// RUN: %target-swift-frontend -build-module-from-parseable-interface -swift-version 5 %t/TestResilient.swiftinterface -o %t/TestResilient.swiftmodule
+// RUN: %target-swift-frontend -emit-module -o /dev/null -merge-modules -swift-version 5  -emit-parseable-module-interface-path - %t/TestResilient.swiftmodule -module-name TestResilient | %FileCheck %s --check-prefix CHECK --check-prefix RESILIENT
+
+@_propertyDelegate
+public struct Wrapper<T> {
+  public var value: T
+}
+
+@_propertyDelegate
+public struct WrapperWithInitialValue<T> {
+  public var value: T
+
+  public init(initialValue: T) {
+    self.value = initialValue
+  }
+
+  public init(alternate value: T) {
+    self.value = value
+  }
+}
+
+// CHECK: public struct HasDelegates {
+public struct HasDelegates {
+  // CHECK: @TestResilient.Wrapper public var x: {{(Swift.)?}}Int {
+  // CHECK-NEXT: get
+  // CHECK-NEXT: set
+  // CHECK-NEXT: }  
+  @Wrapper public var x: Int
+
+  // CHECK: @TestResilient.WrapperWithInitialValue public var y: Swift.Int {
+  // CHECK-NEXT: get
+  // CHECK-NEXT: }  
+  @WrapperWithInitialValue public private(set) var y = 17
+
+  // CHECK: @TestResilient.WrapperWithInitialValue public var z: Swift.Bool {
+  // CHECK-NEXT: get
+  // CHECK-NEXT: set
+  // CHECK-NEXT: }  
+  @WrapperWithInitialValue(alternate: false) public var z
+}