child_process,Windows: deprecate explicit use of cmd.exe

[refack]

• Version: *
• Platform: Windows
• Subsystem: child_process

https://github.com/nodejs/node/blob/master/lib/child_process.js#L444 has a fallback to use cmd.exe in case process.env.ComSpec is falsy.
This is redundant, fragile, and generally covers-up an invalid state (%ComSpec% should always be defined and point to a valid shell executable).
This code path should be deprecated according to the guide at https://github.com/nodejs/node/blob/master/COLLABORATOR_GUIDE.md#deprecations
and https://github.com/nodejs/node/blob/master/doc/api/deprecations.md

Ref: #14149 (comment)

[cjihrig]

@nodejs/platform-windows

[tniessen]

Technically, this is correct, and I don't see a chance of breaking code. Some will probably break due to custom child process environments, but that's what deprecation is for.

[joaocgreis]

So, for users, what this is effectively deprecating is using an environment without %COMSPEC%.

I'm -0 on this. While situations without %COMSPEC% are probably quite messed up already, cmd.exe is a valid fallback and I don't see a pressing reason for deprecating, how this actually translates as an improvement for node.

But discussion is always welcome!

[refack]

I'm -0 on this. While situations without %COMSPEC% are probably quite messed up already, cmd.exe is a valid fallback and I don't see a pressing reason for deprecating, how this actually translates as an improvement for node.

But discussion is always welcome!

1. I opened this as an issue rather than a PR mainly for discussion 😃
2. Literal command strings IMHO are just bad and need a very good reason to exist.
3. In this case it doesn't "solve", just improves the situation by ϵ%. Just as the environment could be missing %COMSPEC%, it could be missing %PATH% (or %WINDIR% so %WINDIR%\system32\cmd.exe isn't any better), and also the system could be missing cmd.exe completely. So if we're just patching over a messed up situation with a only a slightly less messy fix, why bother 🤷‍♂️
4. In general I'm just +0.5 on this whole thing, I just don't like literal command strings in the code

[gireeshpunathil]

Closing as it is inactive for around an year, feel free to re-open if there is anything outstanding.