Add optional FunctionType.positionalParameterNames and use them to resynthesize function-type forma…

pkg/analyzer/lib/src/dart/element/element.dart

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index b4059812a9e3ae697a622fb654871910ef1cf940..9992fbf5cd03b388c08e13920535ab60f7afb413 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -8103,9 +8103,6 @@ class ParameterElementImpl extends VariableElementImpl
 
   @override
   DartType get type {
-    if (_kernel != null) {
-      return _type ??= enclosingUnit._kernelContext.getType(this, _kernel.type);
-    }
     _resynthesizeTypeAndParameters();
     return super.type;
   }
@@ -8217,6 +8214,36 @@ class ParameterElementImpl extends VariableElementImpl
    * been build yet, build them and remember in the corresponding fields.
    */
   void _resynthesizeTypeAndParameters() {
+    if (_kernel != null && _type == null) {
+      kernel.DartType type = _kernel.type;
+      _type = enclosingUnit._kernelContext.getType(this, type);
+      if (type is kernel.FunctionType) {
+        _parameters = new List<ParameterElement>(
+            type.positionalParameters.length + type.namedParameters.length);
+        int index = 0;
+        for (int i = 0; i < type.positionalParameters.length; i++) {
+          String name = i < type.positionalParameterNames.length
+              ? type.positionalParameterNames[i]
+              : null;
+          _parameters[index++] = new ParameterElementImpl.forKernel(
+              enclosingElement,
+              new kernel.VariableDeclaration(name,
+                  type: type.positionalParameters[i]),
+              i < type.requiredParameterCount
+                  ? ParameterKind.REQUIRED
+                  : ParameterKind.POSITIONAL);
+        }
+        for (int i = 0; i < type.namedParameters.length; i++) {
+          _parameters[index++] = new ParameterElementImpl.forKernel(
+              enclosingElement,
+              new kernel.VariableDeclaration(type.namedParameters[i].name,
+                  type: type.namedParameters[i].type),
+              ParameterKind.NAMED);
+        }
+      } else {
+        _parameters = const <ParameterElement>[];
+      }
+    }
     if (_unlinkedParam != null && _declaredType == null && _type == null) {
       if (_unlinkedParam.isFunctionTyped) {
         CompilationUnitElementImpl enclosingUnit = this.enclosingUnit;