Add fix for missing @required params.

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

Index: pkg/analysis_server/lib/src/services/correction/fix_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
index c823e4ebee013b703d53a1ab20670908d52e2da6..eb45caf2cef0f283d9080d42817a773264135a60 100644
--- a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
@@ -267,6 +267,9 @@ class FixProcessor {
       _addFix_createConstructor_insteadOfSyntheticDefault();
       await _addFix_addMissingParameter();
     }
+    if (errorCode == HintCode.MISSING_REQUIRED_PARAM) {
+      _addFix_addMissingRequiredArgument();
+    }
     if (errorCode == StaticWarningCode.FUNCTION_WITHOUT_CALL) {
       _addFix_addMissingMethodCall();
     }
@@ -549,6 +552,57 @@ class FixProcessor {
     }
   }
 
+  void _addFix_addMissingRequiredArgument() {
+    Element targetElement;
+    ArgumentList argumentList;
+
+    if (node is SimpleIdentifier) {
+      AstNode invocation = node.parent;
+      if (invocation is MethodInvocation) {
+        targetElement = invocation.methodName.bestElement;
+        argumentList = invocation.argumentList;
+      } else {
+        AstNode ancestor =
+            invocation.getAncestor((p) => p is InstanceCreationExpression);
+        if (ancestor is InstanceCreationExpression) {
+          targetElement = ancestor.staticElement;
+          argumentList = ancestor.argumentList;
+        }
+      }
+    }
+
+    if (targetElement is ExecutableElement) {
+      List<Expression> args = argumentList.arguments;
+      List<String> namedArgs = args
+          .where((e) => e is NamedExpression)
+          .map((e) => (e as NamedExpression).name.label.name)
+          .toList(growable: false);
+
+      List<ParameterElement> missingParams = targetElement.parameters
+          .where((p) => p.isRequired && !namedArgs.contains(p.name))
+          .toList(growable: false);
+      if (missingParams.isEmpty) {
+        return;
+      }
+
+      // add proposal
+
+      SourceBuilder sb;
+
+      if (args.isEmpty) {
+        sb = new SourceBuilder(file, argumentList.leftParenthesis.end);
+      } else {
+        sb = new SourceBuilder(file, args.last.end);
+        sb.append(', ');
+      }
+
+      sb.append(missingParams.map((p) => '${p.name}: null').join(', '));
+
+      _insertBuilder(sb, targetElement);
+      _addFix(DartFixKind.ADD_MISSING_REQUIRED_ARGUMENT, []);
+    }
+  }
+
   void _addFix_boolInsteadOfBoolean() {
     SourceRange range = rf.rangeError(error);
     _addReplaceEdit(range, 'bool');