support append: true in router navigation methods (close #911)

Author: yyx990803

Diff for: flow/declarations.js

@@ -58,6 +58,7 @@ declare type Location = {
   hash?: string;
   query?: Dictionary<string>;
   params?: Dictionary<string>;
+  append?: boolean;
 }
 
 declare type RawLocation = string | Location

Diff for: src/util/location.js

@@ -36,7 +36,7 @@ export function normalizeLocation (
   const parsedPath = parsePath(next.path || '')
   const basePath = (current && current.path) || '/'
   const path = parsedPath.path
-    ? resolvePath(parsedPath.path, basePath, append)
+    ? resolvePath(parsedPath.path, basePath, append || next.append)
     : (current && current.path) || '/'
   const query = resolveQuery(parsedPath.query, next.query)
   let hash = next.hash || parsedPath.hash

Diff for: test/unit/specs/location.spec.js

@@ -88,6 +88,13 @@ describe('Location utils', () => {
       expect(loc.path).toBe('/fr/foo')
     })
 
+    it('relative append', () => {
+      const loc = normalizeLocation({ path: 'a' }, { path: '/b' }, true)
+      expect(loc.path).toBe('/b/a')
+      const loc2 = normalizeLocation({ path: 'a', append: true }, { path: '/b' })
+      expect(loc2.path).toBe('/b/a')
+    })
+
     it('object', () => {
       const loc = normalizeLocation({
         path: '/abc?foo=bar#hello',