Unify duplicate_field_formal_parameter and final_initialized_multiple_times

I started doing this the normal way, but the two codes appear to differ
only based on whether the field was final, and I don't think that factor
is important to the nature of the error, so I think a single code is
sufficient.

Change-Id: I693dcfb1a2a4b47a8b82fe4860e7a61c82ca062e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/196880
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

pkg/analyzer/lib/error/error.dart

@@ -186,7 +186,6 @@ const List<ErrorCode> errorCodeValues = [
   CompileTimeErrorCode.FIELD_INITIALIZER_REDIRECTING_CONSTRUCTOR,
   CompileTimeErrorCode.FIELD_INITIALIZING_FORMAL_NOT_ASSIGNABLE,
   CompileTimeErrorCode.FINAL_INITIALIZED_IN_DECLARATION_AND_CONSTRUCTOR,
-  CompileTimeErrorCode.FINAL_INITIALIZED_MULTIPLE_TIMES,
   CompileTimeErrorCode.FINAL_NOT_INITIALIZED,
   CompileTimeErrorCode.FINAL_NOT_INITIALIZED_CONSTRUCTOR_1,
   CompileTimeErrorCode.FINAL_NOT_INITIALIZED_CONSTRUCTOR_2,

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

@@ -3168,8 +3168,8 @@ class CompileTimeErrorCode extends AnalyzerErrorCode {
   static const CompileTimeErrorCode DUPLICATE_FIELD_FORMAL_PARAMETER =
       CompileTimeErrorCode(
           'DUPLICATE_FIELD_FORMAL_PARAMETER',
-          "The field '{0}' can't be referenced in multiple initializing "
-              "parameters in the same constructor.",
+          "The field '{0}' can't be initialized by multiple parameters in the "
+              "same constructor.",
           correction: "Try removing one of the parameters, or "
               "using different fields.");
 
@@ -4653,19 +4653,6 @@ class CompileTimeErrorCode extends AnalyzerErrorCode {
           correction: "Try removing one of the initializations.",
           hasPublishedDocs: true);
 
-  /**
-   * 5 Variables: It is a compile-time error if a final instance variable that
-   * has is initialized by means of an initializing formal of a constructor is
-   * also initialized elsewhere in the same constructor.
-   *
-   * Parameters:
-   * 0: the name of the field in question
-   */
-  static const CompileTimeErrorCode FINAL_INITIALIZED_MULTIPLE_TIMES =
-      CompileTimeErrorCode('FINAL_INITIALIZED_MULTIPLE_TIMES',
-          "'{0}' is a final field and so can only be set once.",
-          correction: "Try removing all but one of the initializations.");
-
   /**
    * Parameters:
    * 0: the name of the uninitialized final variable

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

@@ -219,13 +219,7 @@ class ConstructorFieldsVerifier {
             );
           }
         } else if (state == _InitState.initInFieldFormal) {
-          if (fieldElement.isFinal || fieldElement.isConst) {
-            _errorReporter.reportErrorForNode(
-              CompileTimeErrorCode.FINAL_INITIALIZED_MULTIPLE_TIMES,
-              parameter.identifier,
-              [fieldElement.displayName],
-            );
-          }
+          // Reported in DuplicateDefinitionVerifier._checkDuplicateIdentifier
         }
       }
     }

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

@@ -384,14 +384,7 @@ class DuplicateDefinitionVerifier {
 
     var previous = getterScope[name];
     if (previous != null) {
-      if (_isGetterSetterPair(element, previous)) {
-        // OK
-      } else if (element is FieldFormalParameterElement &&
-          previous is FieldFormalParameterElement &&
-          element.field != null &&
-          element.field!.isFinal) {
-        // Reported as CompileTimeErrorCode.FINAL_INITIALIZED_MULTIPLE_TIMES.
-      } else {
+      if (!_isGetterSetterPair(element, previous)) {
         _errorReporter.reportErrorForNode(
           getError(previous, element),
           identifier,

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

@@ -37,6 +37,17 @@ class A {
     ]);
   }
 
+  test_optional_positional_final() async {
+    await assertErrorsInCode(r'''
+class A {
+  final x;
+  A([this.x = 1, this.x = 2]) {}
+}
+''', [
+      error(CompileTimeErrorCode.DUPLICATE_FIELD_FORMAL_PARAMETER, 43, 1),
+    ]);
+  }
+
   test_required_named() async {
     await assertErrorsInCode(r'''
 class A {
@@ -58,4 +69,15 @@ class A {
       error(CompileTimeErrorCode.DUPLICATE_FIELD_FORMAL_PARAMETER, 36, 1),
     ]);
   }
+
+  test_required_positional_final() async {
+    await assertErrorsInCode(r'''
+class A {
+  final x;
+  A(this.x, this.x) {}
+}
+''', [
+      error(CompileTimeErrorCode.DUPLICATE_FIELD_FORMAL_PARAMETER, 38, 1),
+    ]);
+  }
 }

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

@@ -1,39 +0,0 @@
-// Copyright (c) 2019, 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/context_collection_resolution.dart';
-
-main() {
-  defineReflectiveSuite(() {
-    defineReflectiveTests(FinalInitializedMultipleTimesTest);
-  });
-}
-
-@reflectiveTest
-class FinalInitializedMultipleTimesTest extends PubPackageResolutionTest {
-  test_initializingFormals_withDefaultValues() async {
-    await assertErrorsInCode(r'''
-class A {
-  final x;
-  A([this.x = 1, this.x = 2]) {}
-}
-''', [
-      error(CompileTimeErrorCode.FINAL_INITIALIZED_MULTIPLE_TIMES, 43, 1),
-    ]);
-  }
-
-  test_initializingFormals_withoutDefaultValues() async {
-    await assertErrorsInCode(r'''
-class A {
-  final x;
-  A(this.x, this.x) {}
-}
-''', [
-      error(CompileTimeErrorCode.FINAL_INITIALIZED_MULTIPLE_TIMES, 38, 1),
-    ]);
-  }
-}

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

@@ -207,8 +207,6 @@ import 'field_initializing_formal_not_assignable_test.dart'
     as field_initializing_formal_not_assignable;
 import 'final_initialized_in_delcaration_and_constructor_test.dart'
     as final_initialized_in_declaration_and_constructor;
-import 'final_initialized_multiple_times_test.dart'
-    as final_initialized_multiple_times;
 import 'final_not_initialized_constructor_test.dart'
     as final_not_initialized_constructor;
 import 'final_not_initialized_test.dart' as final_not_initialized;
@@ -820,7 +818,6 @@ main() {
     final_initialized_in_declaration_and_constructor.main();
     field_initialized_in_initializer_and_declaration.main();
     field_initialized_in_parameter_and_initializer.main();
-    final_initialized_multiple_times.main();
     field_initializer_factory_constructor.main();
     field_initializer_in_struct.main();
     field_initializer_not_assignable.main();

tests/language/constructor/duplicate_initializers_test.dart

@@ -25,7 +25,7 @@
    Class.two_fields(this.field_
     , this.field_
     //     ^^^^^^
-    // [analyzer] COMPILE_TIME_ERROR.FINAL_INITIALIZED_MULTIPLE_TIMES
+    // [analyzer] COMPILE_TIME_ERROR.DUPLICATE_FIELD_FORMAL_PARAMETER
     // [cfe] 'field_' was already initialized by this constructor.
     //     ^
     // [cfe] Duplicated parameter name 'field_'.

tests/language_2/constructor/duplicate_initializers_test.dart

@@ -27,7 +27,7 @@
    Class.two_fields(this.field_
     , this.field_
     //     ^^^^^^
-    // [analyzer] COMPILE_TIME_ERROR.FINAL_INITIALIZED_MULTIPLE_TIMES
+    // [analyzer] COMPILE_TIME_ERROR.DUPLICATE_FIELD_FORMAL_PARAMETER
     // [cfe] 'field_' was already initialized by this constructor.
     //     ^
     // [cfe] Duplicated parameter name 'field_'.