[Noncopyable] fix subscripts

Author: kavon

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -2718,6 +2718,8 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
   }
 
   void visitSubscriptDecl(SubscriptDecl *SD) {
+    auto *DC = SD->getDeclContext();
+
     // Force requests that can emit diagnostics.
     (void) SD->getInterfaceType();
     (void) SD->getGenericSignature();
@@ -2768,7 +2770,7 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
     checkDefaultArguments(SD->getIndices());
     checkVariadicParameters(SD->getIndices(), SD);
 
-    if (SD->getDeclContext()->getSelfClassDecl()) {
+    if (DC->getSelfClassDecl()) {
       checkDynamicSelfType(SD, SD->getValueInterfaceType());
 
       if (SD->getValueInterfaceType()->hasDynamicSelfType() &&
@@ -2779,15 +2781,15 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
 
     // Reject "class" methods on actors.
     if (SD->getStaticSpelling() == StaticSpellingKind::KeywordClass &&
-        SD->getDeclContext()->getSelfClassDecl() &&
-        SD->getDeclContext()->getSelfClassDecl()->isActor()) {
+        DC->getSelfClassDecl() &&
+        DC->getSelfClassDecl()->isActor()) {
       SD->diagnose(diag::class_subscript_not_in_class, false)
           .fixItReplace(SD->getStaticLoc(), "static");
     }
 
     // Reject noncopyable typed subscripts with read/set accessors since we
     // cannot define modify operations upon them without copying the read.
-    if (SD->getElementInterfaceType()->isNoncopyable()) {
+    if (SD->getElementInterfaceType()->isNoncopyable(DC)) {
       if (auto *read = SD->getAccessor(AccessorKind::Read)) {
         if (!read->isImplicit()) {
           if (auto *set = SD->getAccessor(AccessorKind::Set)) {

test/ModuleInterface/Inputs/NoncopyableGenerics.swift

@@ -0,0 +1,10 @@
+
+
+// A Swift × Haskell stdlib flavour.
+
+public struct Vector<T: ~Copyable> {
+
+  subscript(_ i: UInt) -> T {
+    fatalError("todo")
+  }
+}

test/ModuleInterface/noncopyable_generics.swift

@@ -0,0 +1,7 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend -enable-library-evolution -emit-module -o %t/NoncopyableGenerics.swiftmodule -emit-module-interface-path %t/NoncopyableGenerics.swiftinterface -enable-experimental-feature NoncopyableGenerics %S/Inputs/NoncopyableGenerics.swift
+// RUN: %target-swift-frontend -emit-sil -sil-verify-all -I %t %s > /dev/null
+
+
+import NoncopyableGenerics