npm start fails after copying a generated project to a new directory

Here is the failure:

$ npm start

> bug-test@0.0.1 start /Users/dceddia/Projects/pure-react/sandbox/bug-test-copy
> react-scripts start

module.js:339
    throw err;
    ^

Error: Cannot find module 'cross-spawn'
    at Function.Module._resolveFilename (module.js:337:15)
    at Function.Module._load (module.js:287:25)
    at Module.require (module.js:366:17)
    at require (module.js:385:17)
    at Object.<anonymous> (/Users/dceddia/Projects/pure-react/sandbox/bug-test-copy/node_modules/.bin/react-scripts:3:13)
    at Module._compile (module.js:425:26)
    at Object.Module._extensions..js (module.js:432:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:311:12)
    at Function.Module.runMain (module.js:457:10)

npm ERR! Darwin 14.5.0
npm ERR! argv "/usr/local/Cellar/node/5.0.0/bin/node" "/Users/dceddia/.node/bin/npm" "start"
npm ERR! node v5.0.0
npm ERR! npm  v3.3.12
npm ERR! code ELIFECYCLE
npm ERR! bug-test@0.0.1 start: `react-scripts start`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the bug-test@0.0.1 start script 'react-scripts start'.
npm ERR! Make sure you have the latest version of node.js and npm installed.
npm ERR! If you do, this is most likely a problem with the bug-test package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     react-scripts start
npm ERR! You can get their info via:
npm ERR!     npm owner ls bug-test
npm ERR! There is likely additional logging output above.

npm ERR! Please include the following file with any support request:
npm ERR!     /Users/dceddia/Projects/pure-react/sandbox/bug-test-copy/npm-debug.log

To reproduce:

$ create-react-app bug-test
$ cp -r bug-test bug-test-copy
$ cd bug-test-copy
$ npm start

At first I thought it might have something to do with having run npm start from within bug-test before copying it, but skipping that step didn’t have any effect.

Removing node_modules and reinstalling them fixes it:

$ cd bug-test-copy
$ rm -r node_modules
$ npm install
$ npm start   # works!

Using cp -a instead of cp -r does not cause the problem:

$ create-react-app bug-test
$ cp -a bug-test bug-test-copy
$ cd bug-test-copy
$ npm start   # works!

I’m running Node 5.0.0 and npm 3.3.12.

I tried (via nvm) with Node 6.3.1 and npm 3.10.3 and got the same behavior.

The cp -a vs cp -r makes me think this might be an npm bug.

[kenkoooo]

$ npm install -g npm@latest  # or, npm install -g npm@latest --prefix "C:\Program Files\nodejs"
$ rm -rf node_modules        # or, `cmd /c rmdir /s /q node_modules` on Windows
$ npm install

[latentflip]

I was intrigued so I dug into this real quick.

The problem is that cp -r doesn’t necessarily preserve symlinks, and just copies the file contents instead.

npm run start uses the react-scripts bin file, which is at ./node_modules/.bin/react-scripts however, this should be symlinked into ./node_modules/react-scripts/bin/react-scripts.js. This symlink means that npm can find the cross-spawn module which is a subdependency of react-scripts.

However, cp -r doesn’t preserve that symlink, and instead just copies the contents of the .bin file. npm now doesn’t know to look within the node_modules/react-scripts/node_modules dir to find cross-spawn.

cp -a will preserve symlinks, so avoids the problem.

Looks like diff in general just resolves symlinks and compares the file contents, hence it not spotting this issue.

I’m not sure that this can really be resolved by create-react-app. Perhaps npm should be detecting non-symlinks in ./node_modules/.bin I dunno?