[Type checker] Handle inferred @objc for all accessor kinds.

Due to the wanton use of 'if' rather than 'switch', non-observing,
non-get/set ccessors that got marked '@objc' would cause an
assertion. Fix the materializeForSet case from the bug report as well
as the addressor case.

Fixes SR-5025 / rdar://problem/32426538.

Author: DougGregor

include/swift/AST/DiagnosticsSema.def

@@ -3296,6 +3296,8 @@ ERROR(objc_invalid_on_func_curried,none,
       "cannot be represented in Objective-C", (unsigned))
 ERROR(objc_observing_accessor, none,
       "observing accessors are not allowed to be marked @objc", ())
+ERROR(objc_addressor, none,
+      "addressors are not allowed to be marked @objc", ())
 ERROR(objc_invalid_on_func_variadic,none,
       "method cannot be %" OBJC_ATTR_SELECT "0 because it has a variadic "
       "parameter", (unsigned))

lib/Sema/TypeCheckType.cpp

@@ -3515,17 +3515,36 @@ bool TypeChecker::isRepresentableInObjC(
         return false;
       }
 
-      // willSet/didSet implementations are never exposed to objc, they are
-      // always directly dispatched from the synthesized setter.
-      if (FD->isObservingAccessor()) {
+      switch (FD->getAccessorKind()) {
+      case AccessorKind::NotAccessor:
+        llvm_unreachable("already checking for accessor-ness");
+
+      case AccessorKind::IsDidSet:
+      case AccessorKind::IsWillSet:
+          // willSet/didSet implementations are never exposed to objc, they are
+          // always directly dispatched from the synthesized setter.
         if (Diagnose) {
           diagnose(AFD->getLoc(), diag::objc_observing_accessor);
           describeObjCReason(*this, AFD, Reason);
         }
         return false;
+
+      case AccessorKind::IsGetter:
+      case AccessorKind::IsSetter:
+        return true;
+
+      case AccessorKind::IsMaterializeForSet:
+        // materializeForSet is synthesized, so never complain about it
+        return false;
+
+      case AccessorKind::IsAddressor:
+      case AccessorKind::IsMutableAddressor:
+        if (Diagnose) {
+          diagnose(AFD->getLoc(), diag::objc_addressor);
+          describeObjCReason(*this, AFD, Reason);
+        }
+        return false;
       }
-      assert(FD->isGetterOrSetter() && "missing diags for other accessors");
-      return true;
     }
 
     unsigned ExpectedParamPatterns = 1;

test/attr/attr_objc.swift

@@ -2262,3 +2262,23 @@ extension SubclassInfersFromProtocol2 {
 @objc class NeverReturningMethod {
   @objc func doesNotReturn() -> Never {}
 }
+
+// SR-5025
+class User: NSObject {
+}
+
+@objc extension User {
+	var name: String {
+		get {
+			return "No name"
+		}
+		set {
+			// Nothing
+		}
+	}
+
+	var other: String {
+    unsafeAddress { // expected-error{{addressors are not allowed to be marked @objc}}
+    }
+  }
+}