fix #26812, function types should support the call method

pkg/analyzer/lib/src/generated/element_resolver.dart

Index: pkg/analyzer/lib/src/generated/element_resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/element_resolver.dart b/pkg/analyzer/lib/src/generated/element_resolver.dart
index 029b5c6759abc85ffcba5d66c3c6141a90e70b38..b3dbb0b9eae1e21ccadb020983c69545e9600407 100644
--- a/pkg/analyzer/lib/src/generated/element_resolver.dart
+++ b/pkg/analyzer/lib/src/generated/element_resolver.dart
@@ -643,7 +643,9 @@ class ElementResolver extends SimpleAstVisitor<Object> {
         }
         staticElement = _resolveElement(typeReference, methodName);
       } else {
-        DartType staticType = _getStaticType(target);
+        DartType staticType = _resolver.strongMode
+            ? _getStaticTypeOrFunctionType(target)
+            : _getStaticType(target);
         DartType propagatedType = _getPropagatedType(target);
         staticElement = _resolveInvokedElementWithTarget(
             target, staticType, methodName, isConditional);
@@ -817,6 +819,7 @@ class ElementResolver extends SimpleAstVisitor<Object> {
         }
         return type;
       }
+
       DartType targetType = getSuperType(_getStaticType(target));
       String targetTypeName = targetType?.name;
       _resolver.errorReporter.reportErrorForNode(
@@ -1516,10 +1519,7 @@ class ElementResolver extends SimpleAstVisitor<Object> {
    * type analysis.
    */
   DartType _getStaticType(Expression expression) {
-    if (expression is NullLiteral) {
-      return _resolver.typeProvider.bottomType;
-    }
-    DartType staticType = _resolveTypeParameter(expression.staticType);
+    DartType staticType = _getStaticTypeOrFunctionType(expression);
     if (staticType is FunctionType) {
       //
       // All function types are subtypes of 'Function', which is itself a
@@ -1530,6 +1530,13 @@ class ElementResolver extends SimpleAstVisitor<Object> {
     return staticType;
   }
 
+  DartType _getStaticTypeOrFunctionType(Expression expression) {
+    if (expression is NullLiteral) {
+      return _resolver.typeProvider.bottomType;
+    }
+    return _resolveTypeParameter(expression.staticType);
+  }
+
   /**
    * Check for a generic method & apply type arguments if any were passed.
    */
@@ -2196,6 +2203,10 @@ class ElementResolver extends SimpleAstVisitor<Object> {
       return element;
     } else if (target is SimpleIdentifier) {
       Element targetElement = target.staticElement;
+      if (targetType is FunctionType &&
+          methodName.name == FunctionElement.CALL_METHOD_NAME) {
+        return targetElement;
+      }
       if (targetElement is PrefixElement) {
         if (isConditional) {
           _resolver.errorReporter.reportErrorForNode(