Build: Does not work with Windows + Yarn

[ehmicky]

See #318.

Environment: Windows 10, either cmd.exe or Git Bash.

Example repository: https://github.com/talves/netlify-plugin-debug

Running yarn run netlify-build prints EBADF errors.

Running npx netlify-build works though.

[ehmicky]

Ok so this is probably one of the hardest bugs I've had to debug in a long time. This is my current progress of the understanding of that bug.

Background

@netlify/build is running plugins in child processes. Child processes communicate with parent over std3. We use std3 instead of stdout/stderr so that we can separate plugin outputs from plugin IPC.

In essence, the parent does this:

const {spawn} = require('child_process')
spawn('node', ['child.js'], {stdio: ['inherit', 'inherit', 'inherit', 'pipe']})

The child does this:

const {write} = require('fs')
write(3, 'response', console.log)

This works.

Bug with cmd.exe

However when using yarn run on Windows, the parent ends up doing this:

const {spawn} = require('child_process')
spawn('cmd.exe', ['/c', 'node', 'child.js'], {stdio: ['inherit', 'inherit', 'inherit', 'pipe']})

This results in the following error:

[Error: EBADF: bad file descriptor, write] {
  errno: -4083,
  code: 'EBADF',
  syscall: 'write'
}

This is probably because cmd.exe only forwards stdin, stdout and stderr but not other file descriptors.

Issue with cross-spawn

The reason why yarn run on Windows does this is because we use execa, which itself uses cross-spawn. cross-spawn allows running shebang files on Windows. It does it by prepending cmd.exe /c in front of any non-executable command.

cross-spawn first runs a Node.js port of the which Unix utlity (which itself is basically a hack) on the command. Here the command is node so it usually resolves to C:\Program files\nodejs\node.exe. Since .exe is executable, cross-spawn usually does not need to prepend cmd.exe.

Bug with yarn

However yarn run creates a small node.cmd file in C:\users\me\AppData\Local\Temp\yarn-ID-ID\. That file simplify forwards to the real node.exe:

@"C:\Program files\nodejs\node.exe" %*

That file exists because of Yarn Plug'n'Play and it's basically a hack as well.

When calling yarn run, this small file is run instead of C:\Program files\nodejs\node.exe. It is then prepended to the PATH environment variable so that child processes use that node wrapper as well. However since that file is a .cmd file, cross-spawn needs to prepend cmd.exe /c, which does not work with std3.

I am still investigating this issue, just wanted to report my progress.

[ehmicky]

I fixed this problem by using process.execPath which is the absolute path to node instead of the 'node' string. This short-circuits node-which and solves this bug.

Fixed at #388.

This is released by @netlify/build 0.0.35, which will be included in the next release of @netlify/cli (not done yet).

[ehmicky]

This is fixed in the latest version of @netlify/cli (2.20.1).

[talves]

Woot! @ehmicky all working great on my system now! Confirmed that there is no hanging any longer, also.

Great job on getting this hammered out. Nice to see this fixed in the netlify-cli also.