typeof(voidStmt) now works

[timotheecour]

preferably merge #17813 before this so that CI is green (EDIT: ended up pushing a dummy commit to rerun CI so that it's green because #17813 wasn't merged yet)

• refs https://github.com/nim-lang/Nim/pull/17761/files#r615348636
• closes [superseded] add typetraits.typeOrVoid #17761

this now works:

proc fn() = discard
assert typeof(fn()) is void

likewise with other statements that return void, see tests.

I also added a -d:nimHasTypeofVoid condsyms

note

only 1 place was broken (in cligen) and that was because it used when compiles(type(p)), which is the very thing i'm fixing here. It affected 2 packages (nimterop, prologue) but both orginated from this line; i've sent out c-blake/cligen#193 to fix this with a fwd and backward compatible change, and it was merged (and tagged, which was needed), fixing those 2 packages.

added new PTAL label to help triage issues where ball is in reviewer's camp

@Araq I've added a label PTAL, this is something i've wanted to add for a while and discussed with @xflywind before, the intent is to indicate that a PR is ready for (first or next) round of reviews, meaning some reviewer action is needed, eg:

• all comments are addressed or some comments need reviewer action
• CI is either green or only contains CI failures unrelated to PR (or a [skip ci] was passed before followup #17561, skipping ci now implies green #17813) makes CI for azure red; the benefit being: faster turnaround and avoid wasting CI resources when a commit is deemed safe, eg changelog entry or comment that was verified locally to work with nim doc)
• the PR author, reviewer or anyone can remove the PTAL label when the ball is in PR author's camp

(this feature exists in some form or another in other code review tools)

The goal of PTAL label is to make it easier to identify which PR's need reviewer attention (via github labels) without requiring annoying pings; simply looking at green/red CI status is not a good indication for that (because CI can be green but with unaddressed review comments, or red but still mergeable because of [skip ci] and unrelated CI failures). Of course, both PR author and reviewer need to make sure that this is indeed the case.

example

as you can see in this PR, last commit made it red (changelog only entry with [skip ci] before #17813) but previous commit was green, therefore it is mergeable:

future work

• (pre-existing issue) very similar to when foo: bar puts symbols declared in foo in scope #12030, we should evaluate typeof(x) in its own scope, so that code like this works:

when true:
  var a = 1
  type B = typeof((let a = 2; a))

(see also D20210421T014713 in this PR)

• consider whether we also want this to work:

proc fn() = discard
assert fn() is void