Prioritize required name param completions (flutter-intellij#1049).

pkg/analysis_server/test/services/completion/dart/arglist_contributor_test.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.
 
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/arglist_contributor.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ skipping 77 matching lines @@
     msg.writeln('           found: $actualTypes');
     fail(msg.toString());
   }
 
   /**
    * Assert that the specified named argument suggestions with their types are
    * the only suggestions.
    */
   void assertSuggestArgumentsAndTypes(
       {Map<String, String> namedArgumentsWithTypes,
+      List<int> requiredParamIndices: const <int>[],
       bool includeColon: true,
       bool includeComma: false}) {
     List<CompletionSuggestion> expected = new List<CompletionSuggestion>();
+    int paramIndex = 0;
     namedArgumentsWithTypes.forEach((String name, String type) {
       String completion = includeColon ? '$name: ' : name;
       // Selection should be before any trailing commas.
       int selectionOffset = completion.length;
       if (includeComma) {
         completion = '$completion,';
       }
+      int relevance = requiredParamIndices.contains(paramIndex++)
+          ? DART_RELEVANCE_NAMED_PARAMETER_REQUIRED
+          : DART_RELEVANCE_NAMED_PARAMETER;
       expected.add(assertSuggest(completion,
           csKind: CompletionSuggestionKind.NAMED_ARGUMENT,
-          relevance: DART_RELEVANCE_NAMED_PARAMETER,
+          relevance: relevance,
           paramName: name,
           paramType: type,
           selectionOffset: selectionOffset));
     });
     assertNoOtherSuggestions(expected);
   }
 
   /**
    * Assert that the specified suggestions are the only suggestions.
    */
@@ skipping 735 matching lines @@
 class A { A({int one, String two: 'defaultValue'}) { } }
 main() { new A(^, two: 'foo');}''');
     await computeSuggestions();
 
     assertSuggestArgumentsAndTypes(
         namedArgumentsWithTypes: {'one': 'int'}, includeComma: false);
     assertSuggestArgumentAndCompletion('one',
         completion: 'one: ', selectionOffset: 5);
   }
 
+  test_ArgumentList_local_constructor_required_param_0() async {
+    addMetaPackageSource();
+    addTestSource('''
+import 'package:meta/meta.dart';
+class A { A({int one, @required String two: 'defaultValue'}) { } }
+main() { new A(^);}''');
+    await computeSuggestions();
+    assertSuggestArgumentsAndTypes(
+        namedArgumentsWithTypes: {'one': 'int', 'two': 'String'},
+        requiredParamIndices: [1]);
+  }
+
   test_ArgumentList_local_function_1() async {
     // ArgumentList  MethodInvocation  ExpressionStatement  Block
     addTestSource('''
       import '/libA.dart'
       expect(arg) { }
       class B { }
       String bar() => true;
       void main() {expect(^)}''');
     await computeSuggestions();
     assertSuggestArgumentList(['arg'], ['dynamic']);
@@ skipping 139 matching lines @@
     addTestSource('''
       import '/libA.dart'
       class B {
         expect(arg, int blat) { }
         void foo() {expect(^)}}
       String bar() => true;''');
     await computeSuggestions();
     assertSuggestArgumentList(['arg', 'blat'], ['dynamic', 'int']);
   }
 }