Diagnose invalid @_hasStorage attributes

A bug in `@objc @implementation` is causing incorrect `@_hasStorage` attributes to be printed into module interfaces. As an initial step towards fixing this, diagnose bad `@_hasStorage` attributes and treat them as computed properties so that these malformed interfaces don’t cause compiler crashes.

Partially fixes rdar://144811653.

include/swift/AST/DiagnosticsSema.def

@@ -2216,6 +2216,9 @@ ERROR(invalid_decl_attribute,none,
 ERROR(attr_invalid_on_decl_kind,none,
       "'%0' attribute cannot be applied to %1 declarations",
       (DeclAttribute, DescriptiveDeclKind))
+ERROR(attr_invalid_in_context,none,
+      "'%0' attribute cannot be applied to declaration in %1",
+      (DeclAttribute, DescriptiveDeclKind))
 ERROR(invalid_decl_modifier,none,
       "%0 modifier cannot be applied to this declaration", (DeclAttribute))
 ERROR(attribute_does_not_apply_to_type,none,

lib/Sema/TypeCheckStorage.cpp

@@ -3843,10 +3843,20 @@ StorageImplInfoRequest::evaluate(Evaluator &evaluator,
         : StorageIsMutable);
   }
 
-  if (auto *var = dyn_cast<VarDecl>(storage)) {
+  // If we're in an @implementation extension, we care about the semantics of
+  // the decl it implements.
+  auto *DC = storage->getDeclContext()->getImplementedObjCContext();
+
+  if (auto attr = storage->getParsedAttrs().getAttribute<HasStorageAttr>()) {
+    // If we see `@_hasStorage` in a context with no stored properties, diagnose
+    // and ignore it.
+    if (isa<ExtensionDecl, EnumDecl, ProtocolDecl>(DC)) {
+      storage->diagnose(diag::attr_invalid_in_context, attr,
+                        DC->getAsDecl()->getDescriptiveKind());
+
     // Allow the @_hasStorage attribute to override all the accessors we parsed
     // when making the final classification.
-    if (var->getParsedAttrs().hasAttribute<HasStorageAttr>()) {
+    } else if (auto *var = dyn_cast<VarDecl>(storage)) {
       // The SIL rules for @_hasStorage are slightly different from the non-SIL
       // rules. In SIL mode, @_hasStorage marks that the type is simply stored,
       // and the only thing that determines mutability is the existence of the
@@ -3941,7 +3951,6 @@ StorageImplInfoRequest::evaluate(Evaluator &evaluator,
   bool hasMutableAddress = storage->getParsedAccessor(AccessorKind::MutableAddress);
   bool hasInit = storage->getParsedAccessor(AccessorKind::Init);
 
-  auto *DC = storage->getDeclContext();
   // 'get', 'read', and a non-mutable addressor are all exclusive.
   ReadImplKind readImpl;
   if (storage->getParsedAccessor(AccessorKind::Get)) {

test/ModuleInterface/has_storage_attr_bad.swiftinterface

@@ -0,0 +1,10 @@
+// swift-interface-format-version: 1.0
+// swift-module-flags:
+// expected-error@-2 {{failed to verify module interface of 'Test' due to the errors above}}
+
+// RUN: %target-swift-typecheck-module-from-interface(%s) -module-name Test -verify -verify-ignore-unknown
+// REQUIRES: OS=macosx
+
+extension Array {
+  @_hasStorage public var foo: Int { get set } // expected-error {{'@_hasStorage' attribute cannot be applied to declaration in extension}}
+}

test/SILOptimizer/keypath-folding-crash.sil

@@ -30,7 +30,7 @@ import SwiftShims
 import Builtin
 import CModule
 
-extension ObjClass {
+@objc @implementation extension ObjClass {
   @objc @_hasStorage dynamic var o: NSObject { get set }
 }
 

test/attr/attributes.swift

@@ -308,6 +308,9 @@ class ExclusivityAttrClass {
 class HasStorage {
   @_hasStorage var x : Int = 42  // ok, _hasStorage is allowed here
 }
+extension HasStorage {
+  @_hasStorage var y : Int { 24 } // expected-error {{'@_hasStorage' attribute cannot be applied to declaration in extension}}
+}
 
 @_show_in_interface protocol _underscored {}
 @_show_in_interface class _notapplicable {} // expected-error {{may only be used on 'protocol' declarations}}