Replace 'cstderr.rawWrite' with 'writeToStdErr'

[ehmry]

Use a procedure that is easy to replace on platforms without native UNIX file descriptors.

(#17268 reattempt)

future work

• make writeToStdErr work in VM via a magic/vmops (without resorting to --experimental:compiletimeFFI)
• ditto for js backend, where we can map it to console.log

[ehmry]

I'm not sure if these failed checks are related?

[timotheecour]

Suggested change

	writeFatalErr(buf.cstring, buf.len)
	writeToStdErr buf

I don't think there's a need to introduce writeFatalErr, instead writeToStdErr should be made to work cross platform

[ehmry]

I would prefer to reuse writeToStdErr but I couldn't find an elegant way to do it, writeToStdErr is mostly used in files that are includeed into system.nim, and as I recall system/fatal is imported or included in multiple locations.

[timotheecour]

i think it's fixable, once you fix the other points i can look into how to fix that

[timotheecour]

how about:

  proc writeToStdErr(msg: cstring) {.inlnie.} =
    writeToStdErr(msg, msg.len)

that way, no need to define this overload proc writeToStdErr(msg: cstring) on each platform

[timotheecour]

ditto, this could be defined directly as:

  proc writeToStdErr(msg: string) {.inline.} =
    writeToStdErr(msg.cstring, msg.len)

that way, the only proc to define on each platform is proc writeToStdErr(msg: cstring, length: int)

[timotheecour]

I'm not sure if these failed checks are related?

most likely related, and you should be able to reproduce the bug locally with smthg like
testament pcat dll or similar (these are the failing tests in CI i see)

[ehmry]

I'm not happy with this patch. Its hard to know where define writeToStdErr in system because its used in include files but depends on ansi_c. Would it be better to replace this with an internal compiler builtin instead? I'm willing to make the changes but with the sytem and hardware I'm using its difficult to run the tests.

[Araq]

Why not add it to ansi_c.nim then. Please not another built-in.

[ehmry]

Would this only be valid for C-comptible targets? This is something mostly used in the garbage collector. If it was to go into ansi_c then I would want to change the name to something like writeSystemError, because it wouldn't be UNIX standard error for some platforms.

[Araq]

Would this only be valid for C-comptible targets?

ansi_c.nim would contain the default implementation, you can re-define it with this pattern:

when not declared(writeError):
  proc writeError() = ...

[timotheecour]

ping @ehmry this is a good PR, please continue if you can!

[ehmry]

I don't know the code here well enough to make this change in a way that improves its quality, and I don't think I'm in a position to catch regressions. It would be a welcome improvement, but not something that I have problem with at the moment.