module: check file ext before dir as documented

The documented resolution algorithm was regressed and started to
search for package.json files prior to searching for file extensions
when searching for a specifier. Oddly, it did not search for index
files at same time it searched for package.json. This reverts that
regression and restores the documented behavior of searching for
file extensions prior to searching directories.

Fixes: nodejs#14990
PR-URL: nodejs#15015
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/module.js

@@ -215,6 +215,9 @@ Module._findPath = function(request, paths, isMain) {
   var exts;
   var trailingSlash = request.length > 0 &&
     request.charCodeAt(request.length - 1) === CHAR_FORWARD_SLASH;
+  if (!trailingSlash) {
+    trailingSlash = /(?:^|\/)\.?\.$/.test(request);
+  }
 
   // For each path
   for (var i = 0; i < paths.length; i++) {
@@ -232,10 +235,6 @@ Module._findPath = function(request, paths, isMain) {
         } else {
           filename = toRealPath(basePath);
         }
-      } else if (rc === 1) {  // Directory.
-        if (exts === undefined)
-          exts = Object.keys(Module._extensions);
-        filename = tryPackage(basePath, exts, isMain);
       }
 
       if (!filename) {
@@ -244,14 +243,17 @@ Module._findPath = function(request, paths, isMain) {
           exts = Object.keys(Module._extensions);
         filename = tryExtensions(basePath, exts, isMain);
       }
+
     }
 
     if (!filename && rc === 1) {  // Directory.
+      // try it with each of the extensions at "index"
       if (exts === undefined)
         exts = Object.keys(Module._extensions);
-      filename = tryPackage(basePath, exts, isMain) ||
-        // try it with each of the extensions at "index"
-        tryExtensions(path.resolve(basePath, 'index'), exts, isMain);
+      filename = tryPackage(basePath, exts, isMain);
+      if (!filename) {
+        filename = tryExtensions(path.resolve(basePath, 'index'), exts, isMain);
+      }
     }
 
     if (filename) {

test/fixtures/module-extension-over-directory/inner.js

@@ -0,0 +1 @@
+module.exports = {};

test/fixtures/module-extension-over-directory/inner/package.json

@@ -0,0 +1,3 @@
+{
+  "main": "./package.json"
+}

test/parallel/test-require-extension-over-directory.js

@@ -0,0 +1,26 @@
+'use strict';
+// fixes regression from v4
+require('../common');
+const assert = require('assert');
+const fixtures = require('../common/fixtures');
+const path = require('path');
+
+const fixturesRequire = require(
+  fixtures.path('module-extension-over-directory', 'inner'));
+
+assert.strictEqual(
+  fixturesRequire,
+  require(fixtures.path('module-extension-over-directory', 'inner.js')),
+  'test-require-extension-over-directory failed to import fixture' +
+  ' requirements'
+);
+
+const fakePath = [fixtures.path('module-extension-over-directory', 'inner'), 'fake', '..'].join(path.sep);
+const fixturesRequireDir = require(fakePath);
+
+assert.strictEqual(
+  fixturesRequireDir,
+  require(fixtures.path('module-extension-over-directory', 'inner/')),
+  'test-require-extension-over-directory failed to import fixture' +
+  ' requirements'
+);

test/parallel/test-require-extensions-same-filename-as-dir.js

@@ -28,5 +28,5 @@ const content = require(fixtures.path('json-with-directory-name-module',
                                       'module-stub', 'one', 'two',
                                       'three.js'));
 
-assert.notStrictEqual(content.rocko, 'artischocko');
-assert.strictEqual(content, 'hello from module-stub!');
+assert.strictEqual(content.rocko, 'artischocko');
+assert.notStrictEqual(content, 'hello from module-stub!');