Improve error.killed

[ehmicky]

This changes the conditions behind error.killed.

a) childProcess.kill() was successfully called

true in core Node.js, true in execa. Unchanged.

b) process.kill(childProcess.pid) was called

false in core Node.js, false in execa. Unchanged.

Ideally this should be true, but I am not sure that's possible. The issue is that Windows uses exitCode: 1 and no signal, while Unix uses exitCode: null and signal: 'SIGTERM'. The difference is due to Node.js emulating termination signals on Windows. On Windows (with just exitCode: 1) it seems impossible to know whether the child process was killed externally.

One consequence of this is: while process.kill(childProcess.pid) will set error.killed to false on both Windows and Unix, the error message will be different: was killed with SIGTERM on Unix, failed with exit code 1 on Windows.

c) timeout was reached

true in core Node.js, true in execa. Changed to false with this PR. We have error.timedOut for this. This makes those boolean error properties orthogonal to each other.

d) maxBuffer was reached

true in core Node.js, false in execa. Unchanged. We should add a property similar to error.timedOut but for maxBuffer instead. I can do it in a separate PR.

Note: this not does change childProcess.killed, which is a separate property and is true when childProcess() was successfully called (in both core Node.js and execa).

[sindresorhus]

Can you fix the merge conflict?

[sindresorhus]

On Windows (with just exitCode: 1) it seems impossible to know whether the child process was killed externally.

Should we open an Node.js issue about that?

[ehmicky]

Merge conflict fixed.

I have opened an issue on Node. However I think this PR could still be merged regardless: if that issue resolves, we can create a new PR so that error.killed is true on external signal termination.