Documentation with when branch is missing field types

[mratsim]

Test case: The current options module documentation is missing type for fields:

https://nim-lang.org/docs/options.html#7

Option[T] = object
  when T is SomePointer:
    val
  else:
      val
      has

While this is what is declared:

Nim/lib/pure/options.nim

Lines 75 to 82 in 72e15ff

	type
	Option*[T] = object
	## An optional type that stores its value and state separately in a boolean.
	when T is SomePointer:
	val: T
	else:
	val: T
	has: bool

[nc-x]

This is a general issue not related to docgen:

proc x(n: int): string = discard

x:
  type
    Option*[T] = object
      ## An optional type that stores its value and state separately in a boolean.
      when T is void:
        val: T
      else:
        val: T
        has: bool

nim c t.nim gives -

t.nim(3, 1) Error: type mismatch: got <void>
but expected one of:
proc x(n: int): string

expression: x:
  type
    Option[T] = object
      when T is void:            ## An optional type that stores its value and state separately in a boolean.
        val
      else:
          val
          has

---

This is because semRecordNodeAux for nkRecWhen for generics evaluates stuff early.

A simple fix is to remove this line

Nim/compiler/semtypes.nim

Line 676 in 9c3e23e

it.sons[idx] = if newf.len == 1: newf[0] else: newf

but then obviously it creates other issues.

---

Another fix would be to check for this case here -

Nim/compiler/docgen.nim

Lines 354 to 356 in 9c3e23e

	else:
	dispA(d.conf, result, "<span class=\"Identifier\">$1</span>",
	"\\spanIdentifier{$1}", [rope(esc(d.target, literal))])

and use PSym_variable.typ to get what we want. (And similarly for renderer or whatever the compiler uses to print in errors).

There may be other ways to fix it, IDK.

cc @Araq

[metagn]

Fixed by #21017