Update windows paths to include file:// and fix tests. (mathjax/MathJax#3481).

Author: dpvc

testsuite/tests/util/Context-windows.test.ts

@@ -7,9 +7,10 @@ describe('context object', () => {
 
   test('context', async () => {
     let {context, hasWindow} = await import("#js/util/context.js");
-    expect(context.path('C:\\test.js')).toBe('C:/test.js');
-    expect(context.path('/C:/test.js')).toBe('C:/test.js');
-    expect(context.path('/test.js')).toBe('/test.js');
+    expect(context.path('C:\\test.js')).toBe('file://C:/test.js');
+    expect(context.path('/C:/test.js')).toBe('file://C:/test.js');
+    expect(context.path('/test.js')).toBe('file:///test.js');
+    expect(context.path('./test.js')).toBe('./test.js');
     delete context.path;
     expect(context).toEqual({window: window, document: window.document, os: 'Windows'});
     expect(hasWindow).toBe(true);

ts/util/asyncLoad/system.ts

@@ -27,7 +27,12 @@ import { context } from '../context.js';
 declare const System: { import: (name: string, url?: string) => any };
 declare const __dirname: string;
 
-let root = 'file://' + context.path(__dirname).replace(/\/[^/]*\/[^/]*$/, '/');
+let root =
+  'file://' +
+  context
+    .path(__dirname)
+    .replace(/\/[^/]*\/[^/]*$/, '/')
+    .replace(/^file:\/\//, '');
 
 if (!mathjax.asyncLoad && typeof System !== 'undefined' && System.import) {
   mathjax.asyncLoad = (name: string) => {

ts/util/context.ts

@@ -75,6 +75,6 @@ export const context = {
 if (context.os === 'Windows') {
   context.path = (file: string) =>
     file.match(/^[/\\]?[a-zA-Z]:[/\\]/)
-      ? file.replace(/\\/g, '/').replace(/^\//, '')
-      : file;
+      ? 'file://' + file.replace(/\\/g, '/').replace(/^\//, '')
+      : file.replace(/^\//, 'file:///');
 }