extract field formal contributor from prefixed element contributor

pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart

Index: pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart
new file mode 100644
index 0000000000000000000000000000000000000000..f708685bce8e76a4a0816f4abfb86d6b93d6cbab
--- /dev/null
+++ b/pkg/analysis_server/lib/src/services/completion/dart/field_formal_contributor.dart
@@ -0,0 +1,89 @@
+// Copyright (c) 2014, 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.
+
+library services.completion.contributor.dart.field_formal;
+
+import 'dart:async';
+
+import 'package:analysis_server/src/protocol_server.dart'
+    hide Element, ElementKind;
+import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
+import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
+import 'package:analyzer/src/generated/ast.dart';
+
+/**
+ * A contributor for calculating invocation / access suggestions
+ * `completion.getSuggestions` request results.
+ */
+class FieldFormalContributor extends DartCompletionContributor {
+  @override
+  Future<List<CompletionSuggestion>> computeSuggestions(
+      DartCompletionRequest request) async {
+    if (request.target.containingNode is! FieldFormalParameter) {
+      return EMPTY_LIST;
+    }
+
+    // Partially resolve the compilation unit
+    CompilationUnit unit = await request.resolveDeclarationsInScope();
+    // Gracefully degrade if the compilation unit could not be resolved
+    // e.g. detached part file or source change
+    if (unit == null) {
+      return EMPTY_LIST;
+    }
+
+    // Recompute the target since resolution may have changed it
+    AstNode node = request.target.containingNode;
+    if (node is! FieldFormalParameter) {
+      return EMPTY_LIST;
+    }
+
+    // If this is a constructor declaration
+    // then compute fields already referenced
+    ConstructorDeclaration constructorDecl =
+        node.getAncestor((p) => p is ConstructorDeclaration);
+    if (constructorDecl == null) {
+      return EMPTY_LIST;
+    }
+
+    // Compute the list of fields already referenced in the constructor
+    List<String> referencedFields = new List<String>();
+    for (FormalParameter param in constructorDecl.parameters.parameters) {
+      if (param is FieldFormalParameter) {
+        SimpleIdentifier fieldId = param.identifier;
+        if (fieldId != null && fieldId != request.target.entity) {
+          String fieldName = fieldId.name;
+          if (fieldName != null && fieldName.length > 0) {
+            referencedFields.add(fieldName);
+          }
+        }
+      }
+    }
+
+    // Add suggestions for fields that are not already referenced
+    ClassDeclaration classDecl =
+        constructorDecl.getAncestor((p) => p is ClassDeclaration);
+    List<CompletionSuggestion> suggestions = <CompletionSuggestion>[];
+    for (ClassMember member in classDecl.members) {
+      if (member is FieldDeclaration && !member.isStatic) {
+        for (VariableDeclaration varDecl in member.fields.variables) {
+          SimpleIdentifier fieldId = varDecl.name;
+          if (fieldId != null) {
+            String fieldName = fieldId.name;
+            if (fieldName != null && fieldName.length > 0) {
+              if (!referencedFields.contains(fieldName)) {
+                CompletionSuggestion suggestion = createSuggestion(
+                    fieldId.bestElement,
+                    relevance: DART_RELEVANCE_LOCAL_FIELD);
+                if (suggestion != null) {
+                  suggestions.add(suggestion);
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+    return suggestions;
+  }
+}