feat: loader support load file without extname (#194)

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##### Checklist
<!-- Remove items that do not apply. For completed items, change [ ] to [x]. -->

- [x] `npm test` passes
- [x] tests and/or benchmarks are included
- [ ] documentation is changed or added
- [ ] commit message follows commit guidelines

##### Affected core subsystem(s)
<!-- Provide affected core subsystem(s). -->


##### Description of change
<!-- Provide a description of the change below this comment. -->

Author: whxaxes

lib/loader/egg_loader.js

@@ -291,7 +291,8 @@ class EggLoader {
    * @since 1.0.0
    */
   loadFile(filepath, ...inject) {
-    if (!filepath || !fs.existsSync(filepath)) {
+    filepath = filepath && this.resolveModule(filepath);
+    if (!filepath) {
       return null;
     }
 

lib/loader/mixin/router.js

@@ -14,7 +14,7 @@ module.exports = {
   loadRouter() {
     this.timing.start('Load Router');
     // 加载 router.js
-    this.loadFile(this.resolveModule(path.join(this.options.baseDir, 'app/router')));
+    this.loadFile(path.join(this.options.baseDir, 'app/router'));
     this.timing.end('Load Router');
   },
 };

test/loader/egg_loader.test.js

@@ -61,6 +61,22 @@ describe('test/loader/egg_loader.test.js', () => {
         framework: path.join(__dirname, '../fixtures/egg'),
       });
     });
+
+    it('should loadFile auto resolve file', () => {
+      const loader = new EggLoader({
+        baseDir: path.join(__dirname, '../fixtures/nothing'),
+        app: {},
+        logger: console,
+      });
+
+      let ret = loader.loadFile(path.join(__dirname, '../fixtures/load_file/function.js'), 1, 2);
+      assert(ret[0] === 1);
+      assert(ret[1] === 2);
+
+      ret = loader.loadFile(path.join(__dirname, '../fixtures/load_file/function'), 1, 2);
+      assert(ret[0] === 1);
+      assert(ret[1] === 2);
+    });
   });
 
   it('should be loaded by loadToApp', () => {