Move DEAD_NULL_COALESCE reporting to ErrorVerifier.

So, it is reported even when hints are disabled.

Change-Id: Id2df8faa5421fac00e01755a70aedf3d3f570f10
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/135492
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/lib/src/error/dead_code_verifier.dart

@@ -10,14 +10,12 @@ import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/error/listener.dart';
-import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/dart/resolver/exit_detector.dart';
 import 'package:analyzer/src/dart/resolver/scope.dart';
 import 'package:analyzer/src/error/codes.dart';
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/type_system.dart';
-import 'package:analyzer/src/task/strong/checker.dart';
 
 /// A visitor that finds dead code and unused labels.
 class DeadCodeVerifier extends RecursiveAstVisitor<void> {
@@ -30,9 +28,6 @@ class DeadCodeVerifier extends RecursiveAstVisitor<void> {
   /// The object used to track the usage of labels within a given label scope.
   _LabelTracker labelTracker;
 
-  /// Is `true` if the library being analyzed is non-nullable by default.
-  final bool _isNonNullableByDefault;
-
   /// Initialize a newly created dead code verifier that will report dead code
   /// to the given [errorReporter] and will use the given [typeSystem] if one is
   /// provided.
@@ -44,25 +39,13 @@ class DeadCodeVerifier extends RecursiveAstVisitor<void> {
               isNonNullableByDefault: false,
               strictInference: false,
               typeProvider: null,
-            ),
+            );
-        _isNonNullableByDefault = featureSet.isEnabled(Feature.non_nullable);
-
-  @override
-  void visitAssignmentExpression(AssignmentExpression node) {
-    TokenType operatorType = node.operator.type;
-    if (operatorType == TokenType.QUESTION_QUESTION_EQ) {
-      _checkForDeadNullCoalesce(
-          getReadType(node.leftHandSide), node.rightHandSide);
-    }
-    super.visitAssignmentExpression(node);
-  }
 
   @override
   void visitBinaryExpression(BinaryExpression node) {
     Token operator = node.operator;
     bool isAmpAmp = operator.type == TokenType.AMPERSAND_AMPERSAND;
     bool isBarBar = operator.type == TokenType.BAR_BAR;
-    bool isQuestionQuestion = operator.type == TokenType.QUESTION_QUESTION;
     if (isAmpAmp || isBarBar) {
       Expression lhsCondition = node.leftOperand;
       if (!_isDebugConstant(lhsCondition)) {
@@ -105,9 +88,6 @@ class DeadCodeVerifier extends RecursiveAstVisitor<void> {
 //                return null;
 //              }
 //            }
-    } else if (isQuestionQuestion) {
-      _checkForDeadNullCoalesce(
-          getReadType(node.leftOperand), node.rightOperand);
     }
     super.visitBinaryExpression(node);
   }
@@ -394,17 +374,6 @@ class DeadCodeVerifier extends RecursiveAstVisitor<void> {
     }
   }
 
-  void _checkForDeadNullCoalesce(TypeImpl lhsType, Expression rhs) {
-    if (!_isNonNullableByDefault) return;
-
-    if (_typeSystem.isStrictlyNonNullable(lhsType)) {
-      _errorReporter.reportErrorForNode(
-        StaticWarningCode.DEAD_NULL_COALESCE,
-        rhs,
-      );
-    }
-  }
-
   /// Given some list of [statements], loop through the list searching for dead
   /// statements. If [allowMandated] is true, then allow dead statements that
   /// are mandated by the language spec. This allows for a final break,

pkg/analyzer/lib/src/generated/error_verifier.dart

@@ -35,6 +35,7 @@ import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/parser.dart' show ParserErrorCode;
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/sdk.dart' show DartSdk, SdkLibrary;
+import 'package:analyzer/src/task/strong/checker.dart';
 
 /**
  * A visitor used to traverse an AST structure looking for additional errors and
@@ -342,6 +343,10 @@ class ErrorVerifier extends RecursiveAstVisitor<void> {
     } else {
       _checkForArgumentTypeNotAssignableForArgument(rhs);
     }
+    if (operatorType == TokenType.QUESTION_QUESTION_EQ) {
+      _checkForDeadNullCoalesce(
+          getReadType(node.leftHandSide), node.rightHandSide);
+    }
     _checkForAssignmentToFinal(lhs);
     super.visitAssignmentExpression(node);
   }
@@ -371,6 +376,11 @@ class ErrorVerifier extends RecursiveAstVisitor<void> {
       _checkForArgumentTypeNotAssignableForArgument(node.rightOperand);
     }
 
+    if (type == TokenType.QUESTION_QUESTION) {
+      _checkForDeadNullCoalesce(
+          getReadType(node.leftOperand), node.rightOperand);
+    }
+
     _checkForUseOfVoidResult(node.leftOperand);
 
     super.visitBinaryExpression(node);
@@ -2310,6 +2320,17 @@ class ErrorVerifier extends RecursiveAstVisitor<void> {
     }
   }
 
+  void _checkForDeadNullCoalesce(TypeImpl lhsType, Expression rhs) {
+    if (!_isNonNullableByDefault) return;
+
+    if (_typeSystem.isStrictlyNonNullable(lhsType)) {
+      _errorReporter.reportErrorForNode(
+        StaticWarningCode.DEAD_NULL_COALESCE,
+        rhs,
+      );
+    }
+  }
+
   /**
    * Verify that the given default formal [parameter] is not part of a function
    * typed parameter.

pkg/dev_compiler/tool/dart2js_nnbd_sdk_error_golden.txt

@@ -27,3 +27,8 @@ ERROR|STATIC_WARNING|NEW_WITH_UNDEFINED_CONSTRUCTOR|lib/collection/collection.da
 ERROR|STATIC_WARNING|NEW_WITH_UNDEFINED_CONSTRUCTOR|lib/collection/collection.dart|3026|37|5|The class 'List' doesn't have a constructor named 'empty'.
 ERROR|STATIC_WARNING|NEW_WITH_UNDEFINED_CONSTRUCTOR|lib/internal/internal.dart|1205|37|5|The class 'List' doesn't have a constructor named 'empty'.
 ERROR|STATIC_WARNING|NEW_WITH_UNDEFINED_CONSTRUCTOR|lib/internal/internal.dart|1663|52|5|The class 'List' doesn't have a constructor named 'empty'.
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/_http/http.dart|1463|39|5|The left operand can't be null, so the right operand is never executed.
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/_http/http.dart|8345|60|5|The left operand can't be null, so the right operand is never executed.
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/_http/http.dart|9272|54|5|The left operand can't be null, so the right operand is never executed.
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/html/dart2js/html_dart2js.dart|4075|25|2|The left operand can't be null, so the right operand is never executed.
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/io/io.dart|9167|16|1|The left operand can't be null, so the right operand is never executed.

pkg/dev_compiler/tool/dartdevc_nnbd_sdk_error_golden.txt

@@ -1 +1,7 @@
-
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/_http/http.dart|1463|39|5|The left operand can't be null, so the right operand is never executed.
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/_http/http.dart|8345|60|5|The left operand can't be null, so the right operand is never executed.
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/_http/http.dart|9272|54|5|The left operand can't be null, so the right operand is never executed.
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/collection/collection.dart|1076|46|13|The left operand can't be null, so the right operand is never executed.
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/developer/developer.dart|332|25|23|The left operand can't be null, so the right operand is never executed.
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/html/dart2js/html_dart2js.dart|4075|25|2|The left operand can't be null, so the right operand is never executed.
+WARNING|STATIC_WARNING|DEAD_NULL_COALESCE|lib/io/io.dart|9167|16|1|The left operand can't be null, so the right operand is never executed.

tests/language/nnbd/resolution/question_question_lub_test.dart

@@ -13,10 +13,20 @@ void f1(
     int? nullableInt,
     int nonNullInt,
 ) {
-  (nullableInt ?? nonNullInt) + 1; //# 00: ok
+  (nullableInt ?? nonNullInt) + 1;
-  (nullableInt ?? nullableInt) + 1; //# 01: compile-time error
+  (nullableInt ?? nullableInt) + 1;
-  (nonNullInt ?? nullableInt) + 1; //# 02: compile-time error
+//^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-  (nonNullInt ?? nonNullInt) + 1; //# 03: ok
+// [analyzer] STATIC_WARNING.UNCHECKED_USE_OF_NULLABLE_VALUE
+// [cfe] unspecified
+  (nonNullInt ?? nullableInt) + 1;
+//               ^^^^^^^^^^^
+// [analyzer] STATIC_WARNING.DEAD_NULL_COALESCE
+//^^^^^^^^^^^^^^^^^^^^^^^^^^^
+// [analyzer] STATIC_WARNING.UNCHECKED_USE_OF_NULLABLE_VALUE
+// [cfe] unspecified
+  (nonNullInt ?? nonNullInt) + 1;
+//               ^^^^^^^^^^
+// [analyzer] STATIC_WARNING.DEAD_NULL_COALESCE
 }
 
 // TODO(mfairhurst) add cases with type parameter types

tests/language/nnbd/syntax/nullable_type_ambiguous_test.dart

@@ -37,6 +37,8 @@ main() {
   // { a is bool ?? true : 3 } is parsed as a map literal { ((a is bool) ?? true) : 3 }.
   a = true;
   var x5 = {a is bool ?? true : 3};
+  //                     ^^^^
+  // [analyzer] STATIC_WARNING.DEAD_NULL_COALESCE
   Expect.type<Map<dynamic, dynamic>>(x5);
   Map<dynamic, dynamic> y5 = x5;
 }