fixes #20219; ignore comment/empty node in stmtListExpr

[ringabout]

fixes #20219

[Varriount]

What happens in the following scenario?

var a = 1

proc incrementSideEffect: bool =
  inc(a)
  return true

proc main =
  if incrementSideEffect():
    discard

  echo a

[ringabout]

What happens in the following scenario?

It works as expected and prints 2

function main_452984840() {
  if (incrementSideEffect_452984834()) {
  }
  rawEcho(HEX24_318767107(a_452984833[0]));
}

incrementSideEffect is not a simple expression because it contains two statements.

[AmjadHD]

A case statement seems more suitable:

proc isSimpleExpr(p: PProc; n: PNode): bool =
  # calls all the way down --> can stay expression based
  case n.kind
  of nkCallKinds, nkBracketExpr, nkDotExpr, nkPar, nkTupleConstr, nkObjConstr, nkBracket, nkCurly:
    for c in n:
      if not p.isSimpleExpr(c): return false
    result = true
  of nkStmtListExpr:
    for i in 0..<n.len-1:
      if n[i].kind notin {nkCommentStmt, nkEmpty}: return false
    result = isSimpleExpr(p, n.lastSon)
  elif n.isAtom:
    result = true
  else: discard

[ringabout]

A case statement seems more suitable:

A following up PR is welcome! First we make it correct, then we can make it even faster.

[github-actions]

Thanks for your hard work on this PR!
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