toOpenArray fails when inside nkStmtListExpr

[dom96]

I'm trying to use toOpenArray for a library I'm working on, in order to get around the limitation that procedures cannot return an openarray I am using templates. The problem is that as soon as I introduce any more statements to my template I start getting errors.

Example

template newOpenArray(x: var string, size: int): openArray[char] =
  var z = 1
  toOpenArray(x, z, size)

template doSomethingAndCreate(x: var string): openArray[char] =
  let size = 12
  newOpenArray(x, size)

var x = "asdqweqweqweqwrqwrqwrqwr"
# echo toOpenArray(x, 0, 2)
# echo newOpenArray(x, 12)
echo doSomethingAndCreate(x)

Current Output

a3.nim(13, 26) Error: invalid context for 'toOpenArray';  'toOpenArray' is only valid within a call expression

Expected Output

['s', 'd', 'q', 'w', 'e', 'q', 'w', 'e', 'q', 'w', 'e', 'q']

Possible Solution

ccgcalls.openArrayLoc only checks for the mSlice magic if it appears at the top-level, it doesn't check if it's nested inside a nkStmtListExpr. The code instead moves into the second branch and calls initLocExpr which eventually enters code that raises the exception.

I was able to come up with some really hacky workaround in the compiler code. I'm curious what the correct way to fix this is though, where should this nkStmtListExpr be processed?

Additional Information

$ nim -v
Nim Compiler Version 0.20.99 [MacOSX: amd64]
Compiled at 2019-08-06
Copyright (c) 2006-2019 by Andreas Rumpf

git hash: 8407a574992ebd6bccec647a902cf54a4de8db18
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