`const` procs in `const` array are nil in half of array

[Anuken]

Code

type ProcType = proc()

const a: ProcType = proc() = discard
const arr: array[8, ProcType] = [a, a, a, a, a, a, a, a]

for i in 0..<arr.len:
  echo "[", i, "]: ", arr[i].isNil
echo "\nwith constant index:\n[7]: ", arr[7].isNil

Current Output

[0]: false
[1]: false
[2]: false
[3]: false
[4]: true
[5]: true
[6]: true
[7]: true

with constant index:
[7]: false

Expected Output

[0]: false
[1]: false
[2]: false
[3]: false
[4]: false
[5]: false
[6]: false
[7]: false

with constant index:
[7]: false

Workarounds

• Declaring both the proc and the array as var fixes the problem in this test case. In my codebase, it leads to invalid codegen that I have been unable to isolate.

Additional Information

• Occurs in 1.4.2 as well as latest HEAD
• Occurs with and without --gc:arc
• Likely related to const proc in let array causes invalid codegen #16736

$ nim -v
Nim Compiler Version 1.5.1 [Linux: amd64]
Compiled at 2021-01-16
Copyright (c) 2006-2021 by Andreas Rumpf

44ceefa9fefca58ba32e9638f754d7f4ca8a2b82 (current git head)

[metagn]

Perhaps we can have a new static proc label? More of these issues have been popping up

[cooldome]

I don't think example above should compile. Error message expected on this line:

const a: ProcType = proc() = discard

proc() = discard doesn't have ProcType. Closure vs non-closure proc.

workaround:

type ProcType = proc()

const a: ProcType = proc() {.closure.} = discard
const arr: array[8, ProcType] = [a, a, a, a, a, a, a, a]

for i in 0..<arr.len:
  echo "[", i, "]: ", arr[i].isNil
echo "\nwith constant index:\n[7]: ", arr[7].isNil

[Anuken]

I don't think example above should compile.

You're probably right. I assumed declaring a as ProcType would coerce it to the right type, but that doesn't seem to be happening properly.