Issue 25616. Support for extracting methods with function-typed parameters.

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

 // 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.src.correction.util;
 
 import 'dart:math';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart'
     show SourceChange, SourceEdit;
@@ skipping 1015 matching lines @@
   String getText(int offset, int length) {
     return _buffer.substring(offset, offset + length);
   }
 
   /**
    * Returns the source to reference [type] in this [CompilationUnit].
    *
    * Fills [librariesToImport] with [LibraryElement]s whose elements are
    * used by the generated source, but not imported.
    */
-  String getTypeSource(DartType type, Set<LibraryElement> librariesToImport) {
+  String getTypeSource(DartType type, Set<LibraryElement> librariesToImport,
+      {StringBuffer parametersBuffer}) {
     StringBuffer sb = new StringBuffer();
     // type parameter
     if (!_isTypeVisible(type)) {
       return 'dynamic';
     }
     // just a Function, not FunctionTypeAliasElement
     if (type is FunctionType && type.element is! FunctionTypeAliasElement) {
-      return "Function";
+      if (parametersBuffer == null) {
+        return "Function";
+      }
+      parametersBuffer.write('(');
+      for (ParameterElement parameter in type.parameters) {
+        String parameterType = getTypeSource(parameter.type, librariesToImport);
+        if (parametersBuffer.length != 1) {
+          parametersBuffer.write(', ');
+        }
+        parametersBuffer.write(parameterType);
+        parametersBuffer.write(' ');
+        parametersBuffer.write(parameter.name);
+      }
+      parametersBuffer.write(')');
+      return getTypeSource(type.returnType, librariesToImport);
     }
     // BottomType
     if (type.isBottom) {
       return 'dynamic';
     }
     // prepare element
     Element element = type.element;
     if (element == null) {
       String source = type.toString();
       source = source.replaceAll('<dynamic>', '');
@@ skipping 446 matching lines @@
       _InvertedCondition expr, int newOperatorPrecedence) {
     if (expr._precedence < newOperatorPrecedence) {
       return "(${expr._source})";
     }
     return expr._source;
   }
 
   static _InvertedCondition _simple(String source) =>
       new _InvertedCondition(2147483647, source);
 }