fix: fallback page should use path not file location (#1301)

* fix: fallback page should use path not file location

When resolving fallback page for the path (`fallbackLanguages` option), we should consider the original path, not the file location (which could be different when aliases are used).

* fix: use router.getFile to resolve fallback url

* specs: add cypress test for fallbackLanguages

Co-authored-by: 沈唁 <52o@qq52o.cn>

Author: palkan

cypress/fixtures/tpl/docs.index.html

@@ -28,7 +28,7 @@
       alias: {
         '.*?/awesome':
           'https://raw.githubusercontent.com/docsifyjs/awesome-docsify/master/README.md',
-        '.*?/changelog':
+        '/changelog':
           'https://raw.githubusercontent.com/docsifyjs/docsify/master/CHANGELOG.md',
         '/.*/_navbar.md': '/_navbar.md',
         '/zh-cn/(.*)':
@@ -40,6 +40,7 @@
         '/es/(.*)':
           'https://raw.githubusercontent.com/docsifyjs/docs-es/master/$1'
       },
+      fallbackLanguages: ['es'],
       auto2top: true,
       coverpage: true,
       executeScript: true,

cypress/integration/routing/fallback.spec.js

@@ -0,0 +1,9 @@
+context('config.fallbackLanguages', () => {
+  it('fallbacks respecting aliases', () => {
+    cy.visit('http://localhost:3000/#/es/');
+
+    cy.get('.sidebar-nav').contains('Changelog').click();
+
+    cy.get('#main').should('contain', 'Bug Fixes');
+  })
+});

src/core/fetch/index.js

@@ -123,7 +123,7 @@ export function fetchMixin(proto) {
           this._loadSideAndNav(path, qs, loadSidebar, cb)
         ),
       _ => {
-        this._fetchFallbackPage(file, qs, cb) || this._fetch404(file, qs, cb);
+        this._fetchFallbackPage(path, qs, cb) || this._fetch404(file, qs, cb);
       }
     );
 
@@ -209,7 +209,9 @@ export function fetchMixin(proto) {
       return false;
     }
 
-    const newPath = path.replace(new RegExp(`^/${local}`), '');
+    const newPath = this.router.getFile(
+      path.replace(new RegExp(`^/${local}`), '')
+    );
     const req = request(newPath + qs, true, requestHeaders);
 
     req.then(