Inconsistent multiple extension handling between Module._findPath and Module.load

[sgentle]

Let's start by making a file with multiple extensions: test.foo.bar

> fs.writeFileSync('test.foo.bar', 'NOT_JS', 'utf8')
undefined

So we already know that require.extensions doesn't work with multiple extensions:

> require.extensions['.foo.bar'] = (module, path) => console.log('required .foo.bar', path)
[Function]
> require('./test.foo.bar')
ReferenceError: NOT_JS is not defined
[...stack trace elided...]

And that it will use the last component of the extension instead:

> require.extensions['.bar'] = (module, path) => console.log('required .bar', path)
[Function]
> require('./test.foo.bar')
required .bar /private/tmp/test.foo.bar
{}

Which is all perfectly obvious and by design. But did you know that the path searching uses the whole extension? Which means:

> delete require.extensions['.foo.bar'] // Since it's never called anyway
> require('./test')
Error: Cannot find module './test'
[...stack trace elided...]

However:

> require.extensions['.foo.bar'] = "SURPRISE!"
> require('./test')
required .bar /private/tmp/test.foo.bar
{}

In summary: to hook the requiring of a file with multiple extensions without specifying it, you must:

1. Set require.extensions for the last component of the extension to your hook function
2. Set require.extensions for the entire extension to any value.

This is due to differences in how Module._findPath and Module.load deal with extensions: the former adds each extension in require.extensions to the basename and tests it for existence (via tryExtensions). The latter works the other way around; it removes everything up to the last part of the extension (via path.extname) and then checks if it is present in require.extensions.

I know it's policy not to fix bugs in module that might help compile-to-js languages, but I figure someone else might come across the same problem and this report could be useful to them.

[cjihrig]

What version of Node are you using? The following script (and the variations of it that I tried) work for me on v5.4.1.

'use strict';
const assert = require('assert');
const fs = require('fs');
const file = './test.foo.bar';

fs.writeFileSync(file, 'NOT_JS', 'utf8');

require.extensions['.foo.bar'] = (module, path) => {
  console.log('required .foo.bar', path);
};

assert.throws(() => {
  require(file);
});

require.extensions['.bar'] = (module, path) => {
  console.log('required .bar', path);
};

delete require.extensions['.foo.bar']

assert.doesNotThrow(() => {
  require(file);
});

[sgentle]

Sorry, to be clear, the _findPath/tryExtensions code only happens when the file is required with no extension. Try replacing your last require(file) with require('./test').

[cjihrig]

Ok, here is the reproduction:

'use strict';
const fs = require('fs');

fs.writeFileSync('./test.foo.bar', 'NOT_JS', 'utf8');
require.extensions['.foo.bar'] = (module, path) => {};
// delete require.extensions['.foo.bar'];
require.extensions['.bar'] = (module, path) => {
  console.log(`loaded ${path}`);
};

require('./test');

Toggle the commented out line to see the issue. This seems, to me, like something that should be fixed, but module system. What do others think?

[Trott]

I know it's policy not to fix bugs in module that might help compile-to-js languages, but I figure someone else might come across the same problem and this report could be useful to them.

@sgentle Fortunately, this is no longer true. And while we are unlikely to add new features or change the intended behavior of existing features, fixing bugs in module is now totally on the table. If you feel up to fixing, by all means, please submit a pull request.