[SE-0258] Ban get/set in properties with attached delegates.

Author: DougGregor

include/swift/AST/DiagnosticsSema.def

@@ -4379,6 +4379,9 @@ ERROR(property_delegate_local,none,
 ERROR(property_delegate_let, none,
       "property delegate can only be applied to a 'var'",
       ())
+ERROR(property_delegate_computed, none,
+      "property delegate cannot be applied to a computed property",
+      ())
 
 ERROR(property_with_delegate_conflict_attribute,none,
       "property %0 with a delegate cannot also be "

lib/Sema/TypeCheckPropertyDelegate.cpp

@@ -343,6 +343,12 @@ AttachedPropertyDelegateRequest::evaluate(Evaluator &evaluator,
       }
     }
 
+    // Properties with delegates must not declare a getter or setter.
+    if (!var->hasStorage()) {
+      ctx.Diags.diagnose(attr->getLocation(), diag::property_delegate_computed);
+      return nullptr;
+    }
+
     return mutableAttr;
   }
 

test/SILGen/property_delegates.swift

@@ -142,17 +142,12 @@ struct HasDefaultInit {
 
 struct DelegateWithAccessors {
   @Wrapper
-  var x: Int {
-    // CHECK-LABEL: sil hidden [ossa] @$s18property_delegates21DelegateWithAccessorsV1xSivg
-    // CHECK-NOT: return
-    // CHECK: integer_literal $Builtin.IntLiteral, 42
-    return 42
-
-    // Synthesized setter
-    // CHECK-LABEL: sil hidden [transparent] [ossa] @$s18property_delegates21DelegateWithAccessorsV1xSivs : $@convention(method) (Int, @inout DelegateWithAccessors) -> ()
-    // CHECK-NOT: return
-    // CHECK: struct_element_addr {{%.*}} : $*DelegateWithAccessors, #DelegateWithAccessors.$x
-  }
+  var x: Int
+
+  // Synthesized setter
+  // CHECK-LABEL: sil hidden [transparent] [ossa] @$s18property_delegates21DelegateWithAccessorsV1xSivs : $@convention(method) (Int, @inout DelegateWithAccessors) -> ()
+  // CHECK-NOT: return
+  // CHECK: struct_element_addr {{%.*}} : $*DelegateWithAccessors, #DelegateWithAccessors.$x
 
   mutating func test() {
     x = 17

test/decl/var/property_delegates.swift

@@ -322,25 +322,9 @@ func testBackingStore<T>(bs: BackingStore<T>) {
 // Explicitly-specified accessors
 // ---------------------------------------------------------------------------
 struct DelegateWithAccessors {
-  @Wrapper
+  @Wrapper  // expected-error{{property delegate cannot be applied to a computed property}}
   var x: Int {
-    return $x.value * 2
-  }
-
-  @WrapperWithInitialValue
-  var y: Int {
-    get {
-      return $y.value
-    }
-
-    set {
-      $y.value = newValue / 2
-    }
-  }
-
-  mutating func test() {
-    x = y
-    y = x
+    return 17
   }
 }
 
@@ -520,24 +504,13 @@ class Box<Value> {
 struct UseBox {
   @Box
   var x = 17
-
-  @Box
-  var y: Int {
-    get { return $y.value }
-    set { }
-  }
 }
 
 func testBox(ub: UseBox) {
   _ = ub.x
   ub.x = 5 // expected-error{{cannot assign to property: 'x' is a get-only property}}
 
-  _ = ub.y
-  ub.y = 20 // expected-error{{cannot assign to property: 'ub' is a 'let' constant}}
-
   var mutableUB = ub
-  _ = mutableUB.y
-  mutableUB.y = 20
   mutableUB = ub
 }