Fixes for uninitialized fields of Flutter widgets create constructors in Flutter style.

R=brianwilkerson@google.com, devoncarew@google.com

Bug: https://github.com/flutter/flutter-intellij/issues/2021
Change-Id: Ia5c8989d463ce7071b31069313e4638dea7b13a6
Reviewed-on: https://dart-review.googlesource.com/48700
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analysis_server/lib/src/services/correction/fix_internal.dart

@@ -27,6 +27,7 @@ import 'package:analyzer/error/error.dart';
 import 'package:analyzer/exception/exception.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
+import 'package:analyzer/src/dart/analysis/session_helper.dart';
 import 'package:analyzer/src/dart/analysis/top_level_declaration.dart';
 import 'package:analyzer/src/dart/ast/token.dart';
 import 'package:analyzer/src/dart/ast/utilities.dart';
@@ -107,6 +108,16 @@ class FixProcessor {
    */
   AnalysisDriver driver;
 
+  /**
+   * The analysis session to be used to create the change builder.
+   */
+  AnalysisSession session;
+
+  /**
+   * The helper wrapper around the [session].
+   */
+  AnalysisSessionHelper sessionHelper;
+
   String file;
   CompilationUnitElement unitElement;
   Source unitSource;
@@ -131,7 +142,11 @@ class FixProcessor {
     resourceProvider = dartContext.resourceProvider;
     astProvider = dartContext.astProvider;
     getTopLevelDeclarations = dartContext.getTopLevelDeclarations;
+
     driver = dartContext.analysisDriver;
+    session = driver.currentSession;
+    sessionHelper = new AnalysisSessionHelper(session);
+
     // unit
     unit = dartContext.unit;
     unitElement = unit.element;
@@ -154,11 +169,6 @@ class FixProcessor {
    */
   String get eol => utils.endOfLine;
 
-  /**
-   * Return the analysis session to be used to create the change builder.
-   */
-  AnalysisSession get session => driver.currentSession;
-
   TypeProvider get typeProvider {
     if (_typeProvider == null) {
       _typeProvider = unitElement.context.typeProvider;
@@ -1110,11 +1120,15 @@ class FixProcessor {
     if (node is! SimpleIdentifier || node.parent is! VariableDeclaration) {
       return;
     }
+
     ClassDeclaration classDeclaration =
         node.getAncestor((node) => node is ClassDeclaration);
     if (classDeclaration == null) {
       return;
     }
+    String className = classDeclaration.name.name;
+    InterfaceType superType = classDeclaration.element.supertype;
+
     // prepare names of uninitialized final fields
     List<String> fieldNames = <String>[];
     for (ClassMember member in classDeclaration.members) {
@@ -1130,15 +1144,50 @@ class FixProcessor {
     // prepare location for a new constructor
     ClassMemberLocation targetLocation =
         utils.prepareNewConstructorLocation(classDeclaration);
+
     DartChangeBuilder changeBuilder = new DartChangeBuilder(session);
-    await changeBuilder.addFileEdit(file, (DartFileEditBuilder builder) {
-      builder.addInsertion(targetLocation.offset, (DartEditBuilder builder) {
-        builder.write(targetLocation.prefix);
-        builder.writeConstructorDeclaration(classDeclaration.name.name,
-            fieldNames: fieldNames);
-        builder.write(targetLocation.suffix);
+    if (flutter.isExactlyStatelessWidgetType(superType) ||
+        flutter.isExactlyStatefulWidgetType(superType)) {
+      // Specialize for Flutter widgets.
+      ClassElement keyClass =
+          await sessionHelper.getClass(flutter.WIDGETS_LIBRARY_URI, 'Key');
+      await changeBuilder.addFileEdit(file, (DartFileEditBuilder builder) {
+        builder.addInsertion(targetLocation.offset, (DartEditBuilder builder) {
+          builder.write(targetLocation.prefix);
+          builder.write('const ');
+          builder.write(className);
+          builder.write('({');
+          builder.writeType(keyClass.type);
+          builder.write(' key');
+
+          List<String> childrenFields = [];
+          for (String fieldName in fieldNames) {
+            if (fieldName == 'child' || fieldName == 'children') {
+              childrenFields.add(fieldName);
+              continue;
+            }
+            builder.write(', this.');
+            builder.write(fieldName);
+          }
+          for (String fieldName in childrenFields) {
+            builder.write(', this.');
+            builder.write(fieldName);
+          }
+
+          builder.write('}) : super(key: key);');
+          builder.write(targetLocation.suffix);
+        });
       });
-    });
+    } else {
+      await changeBuilder.addFileEdit(file, (DartFileEditBuilder builder) {
+        builder.addInsertion(targetLocation.offset, (DartEditBuilder builder) {
+          builder.write(targetLocation.prefix);
+          builder.writeConstructorDeclaration(className,
+              fieldNames: fieldNames);
+          builder.write(targetLocation.suffix);
+        });
+      });
+    }
     _addFixFromBuilder(
         changeBuilder, DartFixKind.CREATE_CONSTRUCTOR_FOR_FINAL_FIELDS);
   }
@@ -2965,22 +3014,44 @@ class FixProcessor {
       return;
     }
     ConstructorDeclaration constructor = node.parent;
-    // add these fields
+    List<FormalParameter> parameters = constructor.parameters.parameters;
+
+    ClassDeclaration classNode = constructor.parent;
+    InterfaceType superType = classNode.element.supertype;
+
+    // Compute uninitialized final fields.
     List<FieldElement> fields =
         ErrorVerifier.computeNotInitializedFields(constructor);
     fields.retainWhere((FieldElement field) => field.isFinal);
-    // prepare new parameters code
+
+    // Prepare new parameters code.
     fields.sort((a, b) => a.nameOffset - b.nameOffset);
     String fieldParametersCode =
         fields.map((field) => 'this.${field.name}').join(', ');
-    // prepare the last required parameter
+
+    // Specialize for Flutter widgets.
+    if (flutter.isExactlyStatelessWidgetType(superType) ||
+        flutter.isExactlyStatefulWidgetType(superType)) {
+      if (parameters.isNotEmpty && parameters.last.isNamed) {
+        DartChangeBuilder changeBuilder = new DartChangeBuilder(session);
+        await changeBuilder.addFileEdit(file, (DartFileEditBuilder builder) {
+          builder.addSimpleInsertion(
+              parameters.last.end, ', $fieldParametersCode');
+        });
+        _addFixFromBuilder(
+            changeBuilder, DartFixKind.ADD_FIELD_FORMAL_PARAMETERS);
+        return;
+      }
+    }
+
+    // Prepare the last required parameter.
     FormalParameter lastRequiredParameter;
-    List<FormalParameter> parameters = constructor.parameters.parameters;
     for (FormalParameter parameter in parameters) {
       if (parameter.isRequired) {
         lastRequiredParameter = parameter;
       }
     }
+
     DartChangeBuilder changeBuilder = new DartChangeBuilder(session);
     await changeBuilder.addFileEdit(file, (DartFileEditBuilder builder) {
       // append new field formal initializers

pkg/analysis_server/test/services/correction/fix_test.dart

@@ -596,6 +596,32 @@ class B {}
 ''');
   }
 
+  test_addFieldFormalParameters_flutter() async {
+    addFlutterPackage();
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+class MyWidget extends StatelessWidget {
+  final int a;
+  final int b;
+  final int c;
+
+  MyWidget({Key key, this.a}) : super(key: key);
+}
+''');
+    await assertHasFix(DartFixKind.ADD_FIELD_FORMAL_PARAMETERS, '''
+import 'package:flutter/widgets.dart';
+
+class MyWidget extends StatelessWidget {
+  final int a;
+  final int b;
+  final int c;
+
+  MyWidget({Key key, this.a, this.b, this.c}) : super(key: key);
+}
+''');
+  }
+
   test_addFieldFormalParameters_hasRequiredParameter() async {
     await resolveTestUnit('''
 class Test {
@@ -1623,6 +1649,87 @@ class Test {
 ''');
   }
 
+  test_createConstructor_forFinalFields_flutter() async {
+    addFlutterPackage();
+    errorFilter = (AnalysisError error) {
+      return error.message.contains("'a'");
+    };
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+class MyWidget extends StatelessWidget {
+  final int a;
+  final int b = 2;
+  final int c;
+}
+''');
+    await assertHasFix(DartFixKind.CREATE_CONSTRUCTOR_FOR_FINAL_FIELDS, '''
+import 'package:flutter/widgets.dart';
+
+class MyWidget extends StatelessWidget {
+  final int a;
+  final int b = 2;
+  final int c;
+
+  const MyWidget({Key key, this.a, this.c}) : super(key: key);
+}
+''');
+  }
+
+  test_createConstructor_forFinalFields_flutter_childLast() async {
+    addFlutterPackage();
+    errorFilter = (AnalysisError error) {
+      return error.message.contains("'a'");
+    };
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+class MyWidget extends StatelessWidget {
+  final int a;
+  final Widget child;
+  final int b;
+}
+''');
+    await assertHasFix(DartFixKind.CREATE_CONSTRUCTOR_FOR_FINAL_FIELDS, '''
+import 'package:flutter/widgets.dart';
+
+class MyWidget extends StatelessWidget {
+  final int a;
+  final Widget child;
+  final int b;
+
+  const MyWidget({Key key, this.a, this.b, this.child}) : super(key: key);
+}
+''');
+  }
+
+  test_createConstructor_forFinalFields_flutter_childrenLast() async {
+    addFlutterPackage();
+    errorFilter = (AnalysisError error) {
+      return error.message.contains("'a'");
+    };
+    await resolveTestUnit('''
+import 'package:flutter/widgets.dart';
+
+class MyWidget extends StatelessWidget {
+  final int a;
+  final List<Widget> children;
+  final int b;
+}
+''');
+    await assertHasFix(DartFixKind.CREATE_CONSTRUCTOR_FOR_FINAL_FIELDS, '''
+import 'package:flutter/widgets.dart';
+
+class MyWidget extends StatelessWidget {
+  final int a;
+  final List<Widget> children;
+  final int b;
+
+  const MyWidget({Key key, this.a, this.b, this.children}) : super(key: key);
+}
+''');
+  }
+
   test_createConstructor_insteadOfSyntheticDefault() async {
     await resolveTestUnit('''
 class A {