Multiple constraints with the first is of type void crashes compiler

[alaviss]

Code snippet:

proc gen[A: void, T: void|int](a: A, b: T) = discard

gen[void, void]()     # Works
gen[void, int] 0      # Crash
gen[void, int](b = 0) # Crash

Compiler output:

Hint: used config file '/etc/nim.cfg' [Conf]
Hint: system [Processing]
Hint: crash [Processing]
Traceback from system (most recent call last)
SIGSEGV: Illegal storage access. (Attempt to read from nil?)

nim version:

Nim Compiler Version 0.18.1 [Linux: amd64]
Copyright (c) 2006-2018 by Andreas Rumpf

git hash: cc5140d8b6ea8ca65ec9b74348cf23aec09d6723
active boot switches: -d:release -d:nativeStackTrace

[dom96]

I have a feeling that overloading is something you should be using in this case anyway, and it's the workaround I can think of:

proc gen(a: int, b: int) = discard
proc gen(b: int) = discard

[alaviss]

My use case is something like this:

type
  Context* = object
    impl: pointer
    
  ContextError* = object of Exception
    
proc newCtxPtr(dir: cstring, cfgs: cstringArray): pointer {.importc.}

proc initContext[T: void|string, V: void|openArray[string]](ctx: var Context,
                                                            dir: T,
                                                            cfgs: V) =
  when T is void:
    const cdir = nil
  else:
    let cdir = cstring dir

  when V is void:
    const carr = nil
  else:
    let carr = allocCStringArray cfgs
    defer: deallocCstringArray carr

  ctx.impl = newCtxPtr(cdir, carr)

  if unlikely isNil ctx.impl:
    raise ContextError.newException "Cannot create a Context object"

proc initContext*(): Context =
  initContext[void, void] result

proc initContext*(dir: string): Context =
  initContext[string, void] result, dir

proc initContext*(cfgpaths: openArray[string]): Context =
  initContext[void, openArray[string]] result, cfgpaths

proc initContext*(dir: string, cfgpaths: openArray[string]): Context =
  initContext result, dir, cfgpaths

[narimiran]

proc gen[A: void, T: void|int](a: A, b: T) = discard

Workaround:
Changing the order of params (proc gen[A: void, T: void|int](b: T, a: A) = discard) works.