Issue an error if a prefix in a type name is shadowed by a local vari…

…able.

See #42620.

Change-Id: Ifd18c939082935390df0c2aa0bd724cf6f76c27c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153705
Commit-Queue: Paul Berry <[email protected]>
Reviewed-by: Konstantin Shcheglov <[email protected]>

pkg/analyzer/lib/error/error.dart

@@ -286,6 +286,7 @@ const List<ErrorCode> errorCodeValues = [
   CompileTimeErrorCode.PART_OF_UNNAMED_LIBRARY,
   CompileTimeErrorCode.PREFIX_COLLIDES_WITH_TOP_LEVEL_MEMBER,
   CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT,
+  CompileTimeErrorCode.PREFIX_SHADOWED_BY_LOCAL_DECLARATION,
   CompileTimeErrorCode.PRIVATE_COLLISION_IN_MIXIN_APPLICATION,
   CompileTimeErrorCode.PRIVATE_OPTIONAL_PARAMETER,
   CompileTimeErrorCode.PRIVATE_SETTER,

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

@@ -5589,6 +5589,24 @@ class CompileTimeErrorCode extends AnalyzerErrorCode {
               "prefix, or renaming the prefix.",
           hasPublishedDocs: true);
 
+  /**
+   * From the `Static Types` section of the spec:
+   *
+   *     A type T is malformed if:
+   *     - T has the form id or the form prefix.id, and in the enclosing lexical
+   *       scope, the name id (respectively prefix.id) does not denote a type.
+   *
+   * In particular, this means that if an import prefix is shadowed by a local
+   * declaration, it is an error to try to use it as a prefix for a type name.
+   */
+  static const CompileTimeErrorCode PREFIX_SHADOWED_BY_LOCAL_DECLARATION =
+      CompileTimeErrorCode(
+          'PREFIX_SHADOWED_BY_LOCAL_DECLARATION',
+          "The prefix '{0}' can't be used here because it is shadowed by a "
+              "local declaration.",
+          correction:
+              "Try renaming either the prefix or the local declaration.");
+
   /**
    * It is an error for a mixin to add a private name that conflicts with a
    * private name added by a superclass or another mixin.

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

@@ -1155,6 +1155,7 @@ class ErrorVerifier extends RecursiveAstVisitor<void> {
   @override
   void visitTypeName(TypeName node) {
     _typeArgumentsVerifier.checkTypeName(node);
+    _checkForTypeNamePrefixShadowedByLocal(node);
     super.visitTypeName(node);
   }
 
@@ -4088,6 +4089,21 @@ class ErrorVerifier extends RecursiveAstVisitor<void> {
     }
   }
 
+  void _checkForTypeNamePrefixShadowedByLocal(TypeName node) {
+    var name = node.name;
+    if (name is PrefixedIdentifier &&
+        name.staticElement is TypeDefiningElement) {
+      var prefix = name.prefix;
+      var prefixElement = prefix.staticElement;
+      if (prefixElement != null && prefixElement is! PrefixElement) {
+        _errorReporter.reportErrorForNode(
+            CompileTimeErrorCode.PREFIX_SHADOWED_BY_LOCAL_DECLARATION,
+            prefix,
+            [prefix.name]);
+      }
+    }
+  }
+
   /// Check that none of the type [parameters] references itself in its bound.
   ///
   /// See [StaticTypeWarningCode.TYPE_PARAMETER_SUPERTYPE_OF_ITS_BOUND].

pkg/analyzer/test/src/diagnostics/new_with_non_type_test.dart

@@ -51,6 +51,19 @@ void f() {
     ]);
   }
 
+  test_malformed_constructor_call() async {
+    await assertErrorsInCode('''
+class C {
+  C.x();
+}
+main() {
+  new C.x.y();
+}
+''', [
+      error(StaticWarningCode.NEW_WITH_NON_TYPE, 36, 3),
+    ]);
+  }
+
   test_typeParameter() async {
     await assertErrorsInCode('''
 void foo<T>() {

pkg/analyzer/test/src/diagnostics/prefix_shadowed_by_local_declaration_test.dart

@@ -0,0 +1,69 @@
+// Copyright (c) 2020, 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.
+
+import 'package:analyzer/src/error/codes.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../dart/resolution/driver_resolution.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(PrefixShadowedByLocalDeclarationTest);
+  });
+}
+
+@reflectiveTest
+class PrefixShadowedByLocalDeclarationTest extends DriverResolutionTest {
+  test_function_return_type_not_shadowed_by_parameter() async {
+    await assertNoErrorsInCode('''
+import 'dart:async' as a;
+a.Future f(int a) {
+  return null;
+}
+''');
+  }
+
+  test_local_variable_type_inside_function_with_shadowing_parameter() async {
+    await assertErrorsInCode('''
+import 'dart:async' as a;
+f(int a) {
+  a.Future x = null;
+  return x;
+}
+''', [
+      error(HintCode.UNUSED_IMPORT, 7, 12),
+      error(CompileTimeErrorCode.PREFIX_SHADOWED_BY_LOCAL_DECLARATION, 39, 1),
+    ]);
+  }
+
+  test_local_variable_type_inside_function_with_shadowing_variable_after() async {
+    await assertErrorsInCode('''
+import 'dart:async' as a;
+f() {
+  a.Future x = null;
+  int a = 0;
+  return [x, a];
+}
+''', [
+      error(HintCode.UNUSED_IMPORT, 7, 12),
+      error(CompileTimeErrorCode.REFERENCED_BEFORE_DECLARATION, 34, 1,
+          contextMessages: [message('/test/lib/test.dart', 59, 1)]),
+      error(CompileTimeErrorCode.PREFIX_SHADOWED_BY_LOCAL_DECLARATION, 34, 1),
+    ]);
+  }
+
+  test_local_variable_type_inside_function_with_shadowing_variable_before() async {
+    await assertErrorsInCode('''
+import 'dart:async' as a;
+f() {
+  int a = 0;
+  a.Future x = null;
+  return [x, a];
+}
+''', [
+      error(HintCode.UNUSED_IMPORT, 7, 12),
+      error(CompileTimeErrorCode.PREFIX_SHADOWED_BY_LOCAL_DECLARATION, 47, 1),
+    ]);
+  }
+}

pkg/analyzer/test/src/diagnostics/test_all.dart

@@ -394,6 +394,8 @@ import 'prefix_collides_with_top_level_member_test.dart'
     as prefix_collides_with_top_level_member;
 import 'prefix_identifier_not_followed_by_dot_test.dart'
     as prefix_identifier_not_followed_by_dot;
+import 'prefix_shadowed_by_local_declaration_test.dart'
+    as prefix_shadowed_by_local_declaration;
 import 'private_collision_in_mixin_application_test.dart'
     as private_collision_in_mixin_application;
 import 'private_optional_parameter_test.dart' as private_optional_parameter;
@@ -804,6 +806,7 @@ main() {
     part_of_non_part.main();
     prefix_collides_with_top_level_member.main();
     prefix_identifier_not_followed_by_dot.main();
+    prefix_shadowed_by_local_declaration.main();
     private_collision_in_mixin_application.main();
     private_optional_parameter.main();
     private_setter.main();

tests/language/class/variable_shadow_class_test.dart

@@ -17,7 +17,6 @@ main() {
     var i = new Test.named(10);
     //          ^^^^^^^^^^
     // [analyzer] STATIC_WARNING.CREATION_WITH_NON_TYPE
-    //          ^^^^
     // [cfe] Method not found: 'Test.named'.
     Expect.equals(10, i.field);
   }

tests/language/prefix/shadow_test.dart

@@ -11,6 +11,8 @@ import "../library10.dart" as lib10;
 class P<T> {
   test() {
     new T.Library10(10);
+    //  ^
+    // [analyzer] COMPILE_TIME_ERROR.PREFIX_SHADOWED_BY_LOCAL_DECLARATION
     //    ^
     // [cfe] Method not found: 'T.Library10'.
   }

tests/language_2/class/variable_shadow_class_test.dart

@@ -17,7 +17,6 @@ main() {
     var i = new Test.named(10);
     //          ^^^^^^^^^^
     // [analyzer] STATIC_WARNING.CREATION_WITH_NON_TYPE
-    //          ^^^^
     // [cfe] Method not found: 'Test.named'.
     Expect.equals(10, i.field);
   }

tests/language_2/prefix/shadow_test.dart

@@ -11,6 +11,8 @@ import "../library10.dart" as lib10;
 class P<T> {
   test() {
     new T.Library10(10);
+    //  ^
+    // [analyzer] COMPILE_TIME_ERROR.PREFIX_SHADOWED_BY_LOCAL_DECLARATION
     //    ^
     // [cfe] Method not found: 'T.Library10'.
   }