[SILGen] Don't use assign_by_wrapper for local property wrappers if

there is an initial wrapped value.

Author: hborla

lib/SILGen/SILGenLValue.cpp

@@ -1319,6 +1319,12 @@ namespace {
         if (!(isAssignmentToSelfParamInInit || VD->getDeclContext()->isLocalContext()))
           return false;
 
+        // If this var isn't in a type context, assignment will always use the setter
+        // if there is an initial value.
+        if (!VD->getDeclContext()->isTypeContext() &&
+            wrapperInfo.wrappedValuePlaceholder->getOriginalWrappedValue())
+          return false;
+
         // If we have a nonmutating setter on a value type, the call
         // captures all of 'self' and we cannot rewrite an assignment
         // into an initialization.

test/SILGen/property_wrapper_local.swift

@@ -51,6 +51,20 @@ func testLocalWrapper() {
   // CHECK-LABEL: sil private [ossa] @$s22property_wrapper_local16testLocalWrapperyyF5valueL_Sivs : $@convention(thin) (Int, @guaranteed { var Wrapper<Int> }) -> () {
 }
 
+func testInitialValue() {
+  // CHECK-LABEL: sil hidden [ossa] @$s22property_wrapper_local16testInitialValueyyF : $@convention(thin) () -> () {
+
+  @Wrapper var value: Int = 10
+  // CHECK: function_ref @$s22property_wrapper_local16testInitialValueyyF5valueL_SivpfP : $@convention(thin) (Int) -> Wrapper<Int>
+
+  value = 15
+  // CHECK: function_ref @$s22property_wrapper_local16testInitialValueyyF5valueL_Sivs : $@convention(thin) (Int, @guaranteed { var Wrapper<Int> }) -> ()
+  // CHECK-NOT: assign_by_wrapper
+  // CHECK: return
+
+  // CHECK-LABEL: sil private [ossa] @$s22property_wrapper_local16testInitialValueyyF5valueL_SivpfP : $@convention(thin) (Int) -> Wrapper<Int> {
+}
+
 @propertyWrapper
 enum Lazy<Value> {
   case uninitialized(() -> Value)

test/SILOptimizer/di_property_wrappers_errors.swift

@@ -99,3 +99,23 @@ struct UseWrapperWithAutoclosure {
   } // expected-error{{return from initializer without initializing all stored properties}}
   // expected-note@-1{{'self.wrapped' not initialized}}  
 }
+
+@propertyWrapper
+struct Wrapper<T> {
+  var wrappedValue: T
+}
+
+func local() {
+  var anotherVar: String // expected-note {{variable defined here}}
+
+  @Wrapper var value = 10 {
+    didSet {
+      anotherVar = "hello!"
+    }
+  }
+
+  value = 15 // expected-error {{variable 'anotherVar' used by function definition before being initialized}}
+
+  anotherVar = "hello!"
+  _ = anotherVar
+}