AST: Make sure malscoped extensions get their extended nominal computed

Author: AnthonyLatsis

lib/AST/Decl.cpp

@@ -1245,9 +1245,14 @@ ExtensionDecl::takeConformanceLoaderSlow() {
 }
 
 NominalTypeDecl *ExtensionDecl::getExtendedNominal() const {
-  assert((hasBeenBound() || canNeverBeBound()) &&
-         "Extension must have already been bound (by bindExtensions)");
-  return ExtendedNominal.getPointer();
+  if (hasBeenBound()) {
+    return ExtendedNominal.getPointer();
+  } else if (canNeverBeBound()) {
+    return computeExtendedNominal();
+  }
+
+  llvm_unreachable(
+      "Extension must have already been bound (by bindExtensions)");
 }
 
 NominalTypeDecl *ExtensionDecl::computeExtendedNominal() const {

test/decl/ext/extensions.swift

@@ -37,6 +37,14 @@ protocol NestingTest5 {
 func nestingTest6() {
   extension Foo {} // expected-error {{declaration is only valid at file scope}}
 }
+extension Array {
+  func foo() {
+    extension Array { // expected-error {{declaration is only valid at file scope}}
+    // FIXME: Confusing error
+    // expected-error@-2 {{constrained extension must be declared on the unspecialized generic type 'Array' with constraints specified by a 'where' clause}}
+    }
+  }
+}
 
 //===--- Test that we only allow extensions only for nominal types.
 

validation-test/compiler_crashers_2_fixed/sr15447.swift

@@ -0,0 +1,13 @@
+// RUN: not %target-swift-frontend -typecheck %s
+
+public extension Array {
+    func chunked(into size: Int) -> [[Element]] {
+        return stride(from: 0, to: count, by: size).map { elt in
+            self[elt
+
+
+public extension Array where Element == Item {
+    mutating func toggle(item: Item) -> Bool {
+        _ = contains(item)
+    }
+}