Sorry, I've messed code parts. Here's my report again:

Starting some time ago I can't build jQuery on OS X 10.8.2. It happened when master was on 1.9.0pre and it happens now when it's 2.0.0pre. If I follow instructions and run:

$ npm install
$ grunt

I get an error:

<FATAL> Unable to find "grunt.js" config file. Do you need any --help? </FATAL>

Next, I tried to provide a config file (though it probably means README.md should be corrected):

$ grunt --config Gruntfile.js

but then I get this:

Running "update_submodules" task

Running "selector:src/selector.js" (selector) task
File 'src/selector.js' created.

Running "build:dist/jquery.js:*" (build) task

/usr/local/share/npm/lib/node_modules/grunt/lib/util/task.js:352
          throw e;
                ^
TypeError: Cannot call method 'forEach' of undefined
    at Object.<anonymous> (/Users/mgol/Documents/projects/public/jquery/Gruntfile.js:297:8)
    at Object.task.registerMultiTask.thisTask (/usr/local/share/npm/lib/node_modules/grunt/lib/grunt/task.js:109:15)
    at Object.task.registerTask.thisTask.fn (/usr/local/share/npm/lib/node_modules/grunt/lib/grunt/task.js:58:16)
    at Task.<anonymous> (/usr/local/share/npm/lib/node_modules/grunt/lib/util/task.js:343:36)
    at Task.<anonymous> (/usr/local/share/npm/lib/node_modules/grunt/lib/util/task.js:319:9)
    at Task.<anonymous> (/usr/local/share/npm/lib/node_modules/grunt/lib/util/task.js:346:11)
    at Task.<anonymous> (/usr/local/share/npm/lib/node_modules/grunt/lib/util/task.js:319:9)
    at Task.<anonymous> (/usr/local/share/npm/lib/node_modules/grunt/lib/util/task.js:346:11)
    at Task.<anonymous> (/usr/local/share/npm/lib/node_modules/grunt/lib/util/task.js:319:9)
    at Task.<anonymous> (/usr/local/share/npm/lib/node_modules/grunt/lib/util/task.js:346:11)

I use node from Homebrew, all packages fully updated. npm version is 1.1.69, grunt version is 0.3.17

This isn't the help forum, it's the bug tracker. Please go to forum.jquery.com and post in the Developing jQuery Core forum. Thanks!

OK, posted it here:

https://forum.jquery.com/topic/can-t-build-jquery-on-os-x-10-8-2

I just thought that if build instructions from README.md don't work then it's a bug in documentation but maybe I reached out. Thanks for your response anyway!