real fs called when require is in the trace

[Slayer95]

mock-fs.js

'use strict';

const fs = require('fs');
const path = require('path');
const mock = require('mock-fs');

mock({
    'mock-fs-child.js': fs.readFileSync(path.resolve(__dirname, 'mock-fs-child.js')),
});
require('./mock-fs-child');

mock-fs-child.js

'use strict';

const fs = require('fs');
const path = require('path');

fs.accessSync(path.resolve(__dirname, 'mock-fs.js'));

The accessSync call throws in [email protected], but succeeds despite the file being absent in the sandbox in [email protected].

Node v. 6.3.0

[Slayer95]

I have also been successfully using the real fs module for require module loading up to and including [email protected], with a bit of boilerplate, shown as follows (MIT Licensed)

'use strict';

const fs = require('fs');
const path = require('path');
const Module = require('module');

const mock = require('mock-fs');

const fsSandbox = {
    'mock-fs-child.js': fs.readFileSync(path.resolve(__dirname, 'mock-fs-child.js')),
};
mock.currentSandbox = fsSandbox;

// Node's module loading system should be backed up by the real file system.
Module.__resolveFilename__ = Module._resolveFilename;
Module._resolveFilename = function (request, parent) {
    if (request === 'fs') return this.__resolveFilename__(request, parent);
    mock.restore();
    try {
        return this.__resolveFilename__(request, parent);
    } finally {
        mock(fsSandbox);
    }
};
for (let ext in Module._extensions) {
    let defaultLoader = Module._extensions[ext];
    Module._extensions[ext] = function (module, filename) {
        mock.restore();
        try {
            return defaultLoader(module, filename);
        } finally {
            mock(fsSandbox);
        }
    };
}
Module.prototype.__compile__ = Module.prototype._compile;
Module.prototype._compile = function (content, filename) {
    // Use the sandbox to evaluate the code in our modules.
    mock(fsSandbox);
    try {
        return this.__compile__(content, filename);
    } finally {
        mock.restore();
    }
};

// `watchFile` is unsupported and throws with mock-fs
Object.defineProperty(fs, 'watchFile', {
    get: () => (() => null),
    set: () => null,
});

mock(fsSandbox);
require('./mock-fs-child');

mock-fs-child.js

'use strict';

const fs = require('fs');
const path = require('path');

fs.accessSync(path.resolve(__dirname, 'mock-fs.js'));

Here, the accessSync correctly throws in [email protected] and [email protected], but incorrectly succeeds in [email protected], for Node v4 and v6.
I have also verified that it works in a few of versions of io.js.

If you'd be interested in including it in mock-fs core, note that it's untested in Node v0.12 and below. You'd also probably want to make Module._extensions a Proxy for CoffeeScript support.

[blond]

The PR #139 contains breaking changes.

An example of a package in which the tests are broken after update mock-fs to 3.11.0:

• [email protected] breaks build ⚠️ yandex/tartifacts#21
• [email protected] breaks build 🚨 enb/enb#487

This is not expected behavior for mock-fs. Because it is impossible to write integration tests with [email protected].

I think need to leave behavior from [email protected].

[tschaub]

Would it be possible for you to use proxyquire if you want to override the behavior of require?

@blond - I'd be curious to get some more detail on what functionality you were relying on. As far as I could tell, calling require() after setting up a mock with [email protected] was unreliable at best (it would use the mock filesystem only if corresponding files existed in the real filesystem).

[Slayer95]

@tschaub, this issue happens without overriding require.

Test case in the OP.

[Slayer95]

ping

[Slayer95]

I will probably run a fork with this issue patched

Would you entertain a patch that uses a Proxy to fix the caveat mentioned in the commit message, @tschaub?

[alekbarszczewski]

What can I do to make it work with require('path/to/mocked/module')?

[vjpr]

My use case is that I want require to use the file system for everything except files in a certain directory, and relative requires from anywhere in the mocked directory (i.e. __dirname).

I'm thinking of overriding Module.prototype._compile and using a fs.readFileSync to grab the string contents of the required file myself which should use mock-fs.

[vjpr]

I think if you override Module.resolveFilename then it works. Reading the contents of the file from disk uses fs.readFileSync, whereas resolving the filename with Module._resolveFilename uses something else (process.binding('fs') maybe?) that fs-mock doesn't touch.

[airtonix]

Is this ticket affecting a scenario like so:

// tricky-tool.js
const vfs = require('vinyl-fs');
const nconf = require('nconf').argv();
const map = require('map-stream'):

const IS_MAIN = module.parent || module.parent.id == '.';


function magic (file, done) {
  file.contents = superAwesomeSecretSauce(file.contents);
  done(null, file);
}

module.exports = function go () {
  vfs.src(nconf.source)
    .pipe(map(magic))
    .pipe(vfs.dest(nconf.dest));
}

IS_MAIN && go();

// tricky-tool.spec.js
const mock = require('mock-fs');
const log = require('debug')('test/tricky-tool');
const tape = require('tape');

function beforeEach () {
    log('beforeEach');
    mock({
        'template' : {
            'one.js': 'module.exports = {}',
            'one.json.tmpl': `{
                "something": "foo/{{name}}"
            }`,
            'releaserc.tmpl': `[config]
    something = {{name}}
            `
        }
    });
};

tape('tool is well tricky.', function (test) {
    const doTricks = require('./tricky-tool');
    beforeEach();
    doTricks();
    afterEach();
    test.end();
});

function afterEach () { mock.restore(); }

Here in this case, it seems to have references to both the mock fs and the real fs:

TAP version 13
# converts filenames properly
beforeEach
Template.context 1.77 KB
events.js:183
      throw er; // Unhandled 'error' event
      ^

Error: ENOENT: no such file or directory, lstat '/opt/app/template/one.js'

• Template.context 1.77 KB means it actually required the contents of the package.json on real disk.
• lstat '/opt/app/template/one.js' means it started the vinyl stream with the mocked fs.