Code completion bug fix, don't suggest optional field formal parameters that are already in the con…

pkg/analysis_server/test/services/completion/dart/field_formal_contributor_test.dart

Index: pkg/analysis_server/test/services/completion/dart/field_formal_contributor_test.dart
diff --git a/pkg/analysis_server/test/services/completion/dart/field_formal_contributor_test.dart b/pkg/analysis_server/test/services/completion/dart/field_formal_contributor_test.dart
index 2f3915936a4f21ece4b1f11da8c9645d0e7bc204..cc4d6f8383a9410c4dd024ba456f167aa533825e 100644
--- a/pkg/analysis_server/test/services/completion/dart/field_formal_contributor_test.dart
+++ b/pkg/analysis_server/test/services/completion/dart/field_formal_contributor_test.dart
@@ -164,4 +164,36 @@ class FieldFormalContributorTest extends DartCompletionContributorTest {
     assertNotSuggested('Object');
     assertNotSuggested('==');
   }
+
+  test_ThisExpression_constructor_param_optional() async {
+    // SimpleIdentifier  FieldFormalParameter  FormalParameterList
+    addTestSource('''
+        main() { }
+        class Point {
+          int x;
+          int y;
+          Point({this.x, this.^}) {}
+          ''');
+    await computeSuggestions();
+    expect(replacementOffset, completionOffset);
+    expect(replacementLength, 0);
+    assertSuggestField('y', 'int', relevance: DART_RELEVANCE_LOCAL_FIELD);
+    assertNotSuggested('x');
+  }
+
+  test_ThisExpression_constructor_param_positional() async {
+    // SimpleIdentifier  FieldFormalParameter  FormalParameterList
+    addTestSource('''
+        main() { }
+        class Point {
+          int x;
+          int y;
+          Point({this.x, this.^}) {}
+          ''');
+    await computeSuggestions();
+    expect(replacementOffset, completionOffset);
+    expect(replacementLength, 0);
+    assertSuggestField('y', 'int', relevance: DART_RELEVANCE_LOCAL_FIELD);
+    assertNotSuggested('x');
+  }
 }