Fix rollback Node

Position is not supposed to be extensible, but Node is.
Testing cases for this are also added.

types/vfile/index.d.ts

@@ -18,6 +18,10 @@ declare namespace vfile {
         end: Point;
     }
 
+    interface Node {
+        position: Position;
+    }
+
     interface VFileParamsBase<D> {
         data?: D;
         contents?: Contents;
@@ -43,11 +47,11 @@ declare namespace vfile {
         fatal?: boolean | null;
     }
 
-    type Message = <P extends Position>(reason: string, position?: Point | P, ruleId?: string) => VFileError;
+    type Message = <N extends Node>(reason: string, position?: Point | Position | N, ruleId?: string) => VFileError;
 
-    type Fail = <P extends Position>(reason: string, position?: Point | P, ruleId?: string) => never;
+    type Fail = <N extends Node>(reason: string, position?: Point | Position | N, ruleId?: string) => never;
 
-    type Info = <P extends Position>(reason: string, position?: Point | P, ruleId?: string) => void;
+    type Info = <N extends Node>(reason: string, position?: Point | Position | N, ruleId?: string) => void;
 
     type ToString = (encoding?: BufferEncoding) => string;
 

types/vfile/vfile-tests.ts

@@ -1,4 +1,5 @@
 import vfile = require("vfile");
+import { Point, Position } from "vfile";
 
 const file = vfile({
     path: '~/example.txt',
@@ -28,5 +29,28 @@ console.log(file.messages);
 const custom: string = file.custom; // 'Custom tango'
 const dataCustom: number = file.data.custom; // 12345
 
+// message method accept any Stringifiable Position(e.g. point, position, node with position)
+const startPoint: Point = {
+    line: 1,
+    column: 1,
+};
+const position: Position = {
+    start: startPoint,
+    end: {
+        line: 2,
+        column: 2,
+    }
+};
+// Accept Point
+file.message('test', position);
+// Accept Position
+file.message('test', position);
+// Accept Node with extra value
+file.message('test', {
+    position
+});
+// But, it must reject any malformed position
+file.message({ start: 'invalid point' }); // $ExpectError
+
 // Typings of original properties must be kept
 const fileWithWrongParams = vfile({ path: 1234 }); // $ExpectError