Any field formal parameter has DefaultFieldFormalParameterElementImpl.

pkg/analyzer/test/src/summary/resynthesize_test.dart

Index: pkg/analyzer/test/src/summary/resynthesize_test.dart
diff --git a/pkg/analyzer/test/src/summary/resynthesize_test.dart b/pkg/analyzer/test/src/summary/resynthesize_test.dart
index 9be69724e3d7e8156d2e9e018205d88f06c4442c..c1f45674a7a8611af5eb9e351603bff66a970aea 100644
--- a/pkg/analyzer/test/src/summary/resynthesize_test.dart
+++ b/pkg/analyzer/test/src/summary/resynthesize_test.dart
@@ -1121,6 +1121,22 @@ class E {
     checkLibrary('class C { var x; C(this.x); }');
   }
 
+  test_class_constructor_fieldFormal_named_noDefault() {
+    checkLibrary('class C { int x; C({this.x}); }');
+  }
+
+  test_class_constructor_fieldFormal_named_withDefault() {
+    checkLibrary('class C { int x; C({this.x: 42}); }');
+  }
+
+  test_class_constructor_fieldFormal_optional_noDefault() {
+    checkLibrary('class C { int x; C([this.x]); }');
+  }
+
+  test_class_constructor_fieldFormal_optional_withDefault() {
+    checkLibrary('class C { int x; C([this.x = 42]); }');
+  }
+
   test_class_constructor_implicit() {
     checkLibrary('class C {}');
   }