Issue 29393. Consider 'v ??= doSomething()' as usage of 'v'.

pkg/analyzer/test/generated/hint_code_test.dart

Index: pkg/analyzer/test/generated/hint_code_test.dart
diff --git a/pkg/analyzer/test/generated/hint_code_test.dart b/pkg/analyzer/test/generated/hint_code_test.dart
index f0852ba7191d6869b03c49dad8c2b1e3f635adb0..5a28cffc2e5effb04008d9ff8cd60107af26de50 100644
--- a/pkg/analyzer/test/generated/hint_code_test.dart
+++ b/pkg/analyzer/test/generated/hint_code_test.dart
@@ -2007,45 +2007,45 @@ class A {
     verify([source]);
   }
 
-  test_mustBeImmutable_instance() async {
+  test_mustBeImmutable_extends() async {
     Source source = addSource(r'''
 import 'package:meta/meta.dart';
 @immutable
-class A {
-  static int x;
+class A {}
+class B extends A {
+  int x;
 }
 ''');
     await computeAnalysisResult(source);
-    assertErrors(source, []);
+    assertErrors(source, [HintCode.MUST_BE_IMMUTABLE]);
     verify([source]);
   }
 
-  test_mustBeImmutable_extends() async {
+  test_mustBeImmutable_fromMixin() async {
     Source source = addSource(r'''
 import 'package:meta/meta.dart';
 @immutable
 class A {}
-class B extends A {
+class B {
   int x;
 }
+class C extends A with B {}
 ''');
     await computeAnalysisResult(source);
     assertErrors(source, [HintCode.MUST_BE_IMMUTABLE]);
     verify([source]);
   }
 
-  test_mustBeImmutable_fromMixin() async {
+  test_mustBeImmutable_instance() async {
     Source source = addSource(r'''
 import 'package:meta/meta.dart';
 @immutable
-class A {}
-class B {
-  int x;
+class A {
+  static int x;
 }
-class C extends A with B {}
 ''');
     await computeAnalysisResult(source);
-    assertErrors(source, [HintCode.MUST_BE_IMMUTABLE]);
+    assertErrors(source, []);
     verify([source]);
   }
 
@@ -3742,6 +3742,22 @@ class A {
     verify([source]);
   }
 
+  test_unusedField_notUsed_nullAssign() async {
+    enableUnusedElement = true;
+    Source source = addSource(r'''
+class A {
+  var _f;
+  m() {
+    _f ??= doSomething();
+  }
+}
+doSomething() => 0;
+''');
+    await computeAnalysisResult(source);
+    assertNoErrors(source);
+    verify([source]);
+  }
+
   test_unusedField_notUsed_postfixExpr() async {
     enableUnusedElement = true;
     Source source = addSource(r'''
@@ -4014,6 +4030,21 @@ main() {
     verify([source]);
   }
 
+  test_unusedLocalVariable_isNullAssigned() async {
+    enableUnusedLocalVariable = true;
+    Source source = addSource(r'''
+typedef Foo();
+main() {
+  var v;
+  v ??= doSomething();
+}
+doSomething() => 42;
+''');
+    await computeAnalysisResult(source);
+    assertErrors(source);
+    verify([source]);
+  }
+
   test_unusedLocalVariable_isRead_notUsed_compoundAssign() async {
     enableUnusedLocalVariable = true;
     Source source = addSource(r'''