Avoid objcImpl @_hasStorage in module interfaces

If an `@objc implementation extension` had a public stored property with an observer, Swift would print `@_hasStorage` on the extension. This is Not Good because in a module interface, an objcImpl extension appears to be an ordinary extension, and properties in ordinary extensions are not supposed to have storage.

Suppress printing this attribute in objcImpl extensions to avoid this problem.

Partially fixes rdar://144811653 by suppressing emission of bad attributes.

Author: beccadax

lib/AST/ASTPrinter.cpp

@@ -1332,8 +1332,8 @@ void PrintAST::printAttributes(const Decl *D) {
 
       if (!Options.PrintForSIL) {
         // Don't print @_hasStorage if the value is simply stored, or the
-        // decl is resilient.
-        if (vd->isResilient() ||
+        // decl is resilient or in an `@objc @implementation` extension.
+        if (vd->isResilient() || isInObjCImpl(vd) ||
             (vd->getImplInfo().isSimpleStored() &&
              !hasLessAccessibleSetter(vd)))
           Options.ExcludeAttrList.push_back(DeclAttrKind::HasStorage);

test/ModuleInterface/objc_implementation.swift

@@ -21,6 +21,9 @@ import Foundation
 // @objc should be omitted on extensions
 // NEGATIVE-NOT: @objc{{.*}} extension
 
+// Stored properties in objcImpl extensions shouldn't have @_hasStorage
+// NEGATIVE-NOT: @_hasStorage
+
 //
 // @_objcImplementation class
 //
@@ -42,6 +45,11 @@ import Foundation
   // CHECK-DAG: final public var implProperty2: ObjectiveC.NSObject? { get set }
   public final var implProperty2: NSObject?
 
+  // CHECK-DAG: final public var implProperty3: ObjectiveC.NSObject? {
+  public final var implProperty3: NSObject? {
+    didSet { }
+  }
+
   // CHECK-NOT: func mainMethod
   @objc public func mainMethod(_: Int32) { print(implProperty) }