module: support multi-dot file extension

Support multi-dot file extensions like '.coffee.md' in Module.load.

PR-URL: #23416
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: John-David Dalton <john.david.dalton@gmail.com>

lib/internal/modules/cjs/loader.js

@@ -219,6 +219,22 @@ function tryExtensions(p, exts, isMain) {
   return false;
 }
 
+// find the longest (possibly multi-dot) extension registered in
+// Module._extensions
+function findLongestRegisteredExtension(filename) {
+  const name = path.basename(filename);
+  let currentExtension;
+  let index;
+  let startIndex = 0;
+  while ((index = name.indexOf('.', startIndex)) !== -1) {
+    startIndex = index + 1;
+    if (index === 0) continue; // Skip dotfiles like .gitignore
+    currentExtension = name.slice(index);
+    if (Module._extensions[currentExtension]) return currentExtension;
+  }
+  return '.js';
+}
+
 var warned = false;
 Module._findPath = function(request, paths, isMain) {
   if (path.isAbsolute(request)) {
@@ -600,8 +616,7 @@ Module.prototype.load = function(filename) {
   this.filename = filename;
   this.paths = Module._nodeModulePaths(path.dirname(filename));
 
-  var extension = path.extname(filename) || '.js';
-  if (!Module._extensions[extension]) extension = '.js';
+  var extension = findLongestRegisteredExtension(filename);
   Module._extensions[extension](this, filename);
   this.loaded = true;
 

test/parallel/test-module-multi-extensions.js

@@ -0,0 +1,94 @@
+'use strict';
+
+// Refs: https://github.com/nodejs/node/issues/4778
+
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs');
+const path = require('path');
+const Module = require('module');
+const tmpdir = require('../common/tmpdir');
+const file = path.join(tmpdir.path, 'test-extensions.foo.bar');
+const dotfile = path.join(tmpdir.path, '.bar');
+const dotfileWithExtension = path.join(tmpdir.path, '.foo.bar');
+
+tmpdir.refresh();
+fs.writeFileSync(file, 'console.log(__filename);', 'utf8');
+fs.writeFileSync(dotfile, 'console.log(__filename);', 'utf8');
+fs.writeFileSync(dotfileWithExtension, 'console.log(__filename);', 'utf8');
+
+{
+  require.extensions['.bar'] = common.mustNotCall();
+  require.extensions['.foo.bar'] = common.mustCall();
+  const modulePath = path.join(tmpdir.path, 'test-extensions');
+  require(modulePath);
+  require(file);
+  delete require.cache[file];
+  delete require.extensions['.bar'];
+  delete require.extensions['.foo.bar'];
+  Module._pathCache = Object.create(null);
+}
+
+{
+  require.extensions['.foo.bar'] = common.mustCall();
+  const modulePath = path.join(tmpdir.path, 'test-extensions');
+  require(modulePath);
+  assert.throws(
+    () => require(`${modulePath}.foo`),
+    new Error(`Cannot find module '${modulePath}.foo'`)
+  );
+  require(`${modulePath}.foo.bar`);
+  delete require.cache[file];
+  delete require.extensions['.foo.bar'];
+  Module._pathCache = Object.create(null);
+}
+
+{
+  const modulePath = path.join(tmpdir.path, 'test-extensions');
+  assert.throws(
+    () => require(modulePath),
+    new Error(`Cannot find module '${modulePath}'`)
+  );
+  delete require.cache[file];
+  Module._pathCache = Object.create(null);
+}
+
+{
+  require.extensions['.bar'] = common.mustNotCall();
+  require.extensions['.foo.bar'] = common.mustCall();
+  const modulePath = path.join(tmpdir.path, 'test-extensions.foo');
+  require(modulePath);
+  delete require.cache[file];
+  delete require.extensions['.bar'];
+  delete require.extensions['.foo.bar'];
+  Module._pathCache = Object.create(null);
+}
+
+{
+  require.extensions['.foo.bar'] = common.mustNotCall();
+  const modulePath = path.join(tmpdir.path, 'test-extensions.foo');
+  assert.throws(
+    () => require(modulePath),
+    new Error(`Cannot find module '${modulePath}'`)
+  );
+  delete require.extensions['.foo.bar'];
+  Module._pathCache = Object.create(null);
+}
+
+{
+  require.extensions['.bar'] = common.mustNotCall();
+  require(dotfile);
+  delete require.cache[dotfile];
+  delete require.extensions['.bar'];
+  Module._pathCache = Object.create(null);
+}
+
+{
+  require.extensions['.bar'] = common.mustCall();
+  require.extensions['.foo.bar'] = common.mustNotCall();
+  require(dotfileWithExtension);
+  delete require.cache[dotfileWithExtension];
+  delete require.extensions['.bar'];
+  delete require.extensions['.foo.bar'];
+  Module._pathCache = Object.create(null);
+}