[dart2js] fix inference of ??= and []??=

Fixes #24134
Fixes #24135

[email protected], [email protected]

Review URL: https://codereview.chromium.org//1305663002 .

Author: sigmundch

pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart

@@ -799,8 +799,6 @@ class SimpleTypeInferrerVisitor<T>
         elements.getGetterSelectorInComplexSendSet(node);
     TypeMask getterMask =
         elements.getGetterTypeMaskInComplexSendSet(node);
-    Selector operatorSelector =
-        elements.getOperatorSelectorInComplexSendSet(node);
     TypeMask operatorMask =
         elements.getOperatorTypeMaskInComplexSendSet(node);
     Selector setterSelector = elements.getSelector(node);
@@ -859,53 +857,53 @@ class SimpleTypeInferrerVisitor<T>
           node, element, setterSelector, setterMask, receiverType, rhsType,
           node.arguments.head);
     } else {
-      // [: foo++ :] or [: foo += 1 :].
-      ArgumentsTypes operatorArguments = new ArgumentsTypes<T>([rhsType], null);
+      // [foo ??= bar], [: foo++ :] or [: foo += 1 :].
       T getterType;
       T newType;
-      if (Elements.isErroneous(element)) {
-        getterType = types.dynamicType;
-        newType = types.dynamicType;
-      } else if (Elements.isStaticOrTopLevelField(element)) {
+
+      if (Elements.isErroneous(element)) return types.dynamicType;
+
+      if (Elements.isStaticOrTopLevelField(element)) {
         Element getterElement = elements[node.selector];
         getterType = handleStaticSend(
             node, getterSelector, getterMask, getterElement, null);
-        newType = handleDynamicSend(
-            node, operatorSelector, operatorMask,
-            getterType, operatorArguments);
-        handleStaticSend(
-            node, setterSelector, setterMask, element,
-            new ArgumentsTypes<T>([newType], null));
       } else if (Elements.isUnresolved(element)
                  || element.isSetter
                  || element.isField) {
         getterType = handleDynamicSend(
             node, getterSelector, getterMask, receiverType, null);
-        newType = handleDynamicSend(
-            node, operatorSelector, operatorMask,
-            getterType, operatorArguments);
-        handleDynamicSend(node, setterSelector, setterMask, receiverType,
-                          new ArgumentsTypes<T>([newType], null));
       } else if (element.isLocal) {
         LocalElement local = element;
         getterType = locals.use(local);
-        newType = handleDynamicSend(
-            node, operatorSelector, operatorMask,
-            getterType, operatorArguments);
-        locals.update(element, newType, node);
       } else {
         // Bogus SendSet, for example [: myMethod += 42 :].
         getterType = types.dynamicType;
+      }
+
+      if (op == '??=') {
+        newType = types.allocateDiamondPhi(getterType, rhsType);
+      } else {
+        Selector operatorSelector =
+          elements.getOperatorSelectorInComplexSendSet(node);
         newType = handleDynamicSend(
             node, operatorSelector, operatorMask,
-            getterType, operatorArguments);
+            getterType, new ArgumentsTypes<T>([rhsType], null));
       }
 
-      if (node.isPostfix) {
-        return getterType;
-      } else {
-        return newType;
+      if (Elements.isStaticOrTopLevelField(element)) {
+        handleStaticSend(
+            node, setterSelector, setterMask, element,
+            new ArgumentsTypes<T>([newType], null));
+      } else if (Elements.isUnresolved(element)
+                 || element.isSetter
+                 || element.isField) {
+        handleDynamicSend(node, setterSelector, setterMask, receiverType,
+                          new ArgumentsTypes<T>([newType], null));
+      } else if (element.isLocal) {
+        locals.update(element, newType, node);
       }
+
+      return node.isPostfix ? getterType : newType;
     }
   }
 
@@ -932,12 +930,18 @@ class SimpleTypeInferrerVisitor<T>
         getterMask,
         receiverType,
         new ArgumentsTypes<T>([indexType], null));
-    T returnType = handleDynamicSend(
-        node,
-        operatorSelector,
-        operatorMask,
-        getterType,
-        new ArgumentsTypes<T>([rhsType], null));
+
+    T returnType;
+    if (node.isIfNullAssignment) {
+      returnType = types.allocateDiamondPhi(getterType, rhsType);
+    } else {
+      returnType = handleDynamicSend(
+          node,
+          operatorSelector,
+          operatorMask,
+          getterType,
+          new ArgumentsTypes<T>([rhsType], null));
+    }
     handleDynamicSend(
         node,
         setterSelector,

tests/compiler/dart2js_extra/if_null2_test.dart

@@ -0,0 +1,15 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Regression for #24134: inference was not tracking ??= correctly.
+library tests.compiler.dart2js_extra.if_null2_test;
+
+import "package:expect/expect.dart";
+
+main() {
+  var map;
+  map ??= {};
+  Expect.equals(0, map.length);
+  Expect.isTrue(map.length == 0);
+}

tests/compiler/dart2js_extra/if_null3_test.dart

@@ -0,0 +1,14 @@
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Regression for #24135: inference was not tracking `[]??=` correctly.
+library tests.compiler.dart2js_extra.if_null3_test;
+
+import "package:expect/expect.dart";
+
+void main() {
+  var map;
+  (((map ??= {})['key1'] ??= {})['key2'] ??= {})['key3'] = 'value';
+  Expect.equals('{key1: {key2: {key3: value}}}', '$map');
+}

tests/compiler/dart2js_extra/if_null_test.dart

@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// SharedOptions=--enable-null-aware-operators
 import "package:expect/expect.dart";
 
 @NoInline() @AssumeDynamic()

tests/language/language_dart2js.status

@@ -120,7 +120,6 @@ regress_22976_test/02: CompileTimeError # Issue 23132
 
 if_null_assignment_behavior_test/13: Crash # Issue 23491
 if_null_assignment_behavior_test/14: Crash # Issue 23491
-nullaware_opt_test: Fail # Fails at e?.f ??= 200;
 
 if_null_assignment_behavior_test/29: Crash # Issue 23611
 prefix_assignment_test/01: Crash # Issue 23611