brew: Can't upgrade npm within node@4 on fresh brew install with its only package

Much has been said about brew/node/npm and permissions problems. Today I’ve encountered a configuration I haven’t seen before, so maybe it’s worth reporting.

Prerequisite: completely pristine OSX, no previous Homebrew files around

1. Install brew: /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
2. Observe that /usr/local/lib is empty
3. Install node4: brew install node@4
4. Observe that there is now /usr/local/lib/node_modules/
5. Run npm install -g npm

💥

npm ERR! Darwin 16.4.0
npm ERR! argv "/usr/local/Cellar/node@4/4.8.0/bin/node" "/usr/local/bin/npm" "install" "-g" "npm"
npm ERR! node v4.8.0
npm ERR! npm  v2.15.11
npm ERR! path /usr/local/lib
npm ERR! code EACCES
npm ERR! errno -13
npm ERR! syscall rmdir

npm ERR! Error: EACCES: permission denied, rmdir '/usr/local/lib'
npm ERR!     at Error (native)
npm ERR!  { [Error: EACCES: permission denied, rmdir '/usr/local/lib']
npm ERR!   errno: -13,
npm ERR!   code: 'EACCES',
npm ERR!   syscall: 'rmdir',
npm ERR!   path: '/usr/local/lib' }
npm ERR!
npm ERR! Please try running this command again as root/Administrator.

npm ERR! Please include the following file with any support request:
npm ERR!     /Users/user/npm-debug.log

At this point things are completely foobar because npm and node_modules were removed and no other version installed.

A quick fix is to uninstall/install the brew package: brew uninstall node@4 && brew install node@4

Fun fact: if there is anything else in /usr/local/lib/, it works!

Same procedure as above, with a new 5):

1. Install brew: /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
2. Observe that /usr/local/lib is empty
3. Install node4: brew install node@4
4. Observe that there is now /usr/local/lib/node_modules/
5. touch /usr/local/lib/dummy
6. Run npm install -g npm

Everything works 🚀

It is my understanding this is more likely a problem of how npm itself works and not a brew issue.

Note that this is when upgrading from node4’s npm which is version 2.

I did not encounter such problems when I manually jumped e.g. from npm 4 to 3 or such, so this seems not a current bug of npm anymore.

But since an older version of npm is installed here, maybe brew can do something as a workaround.

thanks!