typeof(default(T)[]) cannot be manipulated in macros

[mratsim]

Building on the solution for #13048 (comment)

import macros

macro foo*(T: typedesc): typedesc =
  echo T.getTypeInst.treerepr
  echo "--------------------------------------"
  let instantiated = T.getTypeInst
  echo instantiated.treeRepr[1] # This is the char 'r'

  return getType(int)

type
  Task = ptr object
    prev, next: Task
    parent: Task
    fn: proc (param: pointer) {.nimcall.}
    # User data
    data: array[10, byte]

discard foo(typeof(default(Task)[]))

The instantiated.treeRepr returns the character 'r' which is very strange.

Output

BracketExpr
  Sym "typeDesc"
  Sym "Task:ObjectType"
--------------------------------------
r

[ghost]

You just called treerepr too early. You're indexing a string, not a NimNode.

[mratsim]

That's not it.

If you look closely

  echo T.getTypeInst.treerepr
  echo "--------------------------------------"

returns

BracketExpr
  Sym "typeDesc"
  Sym "Task:ObjectType"
--------------------------------------

So instantiated[1] => T.getTypeInst[1] should return Sym "Task:ObjectType"

If you add an extra line that display the type you can confirm that it returns a char instead of a nnkSym.

import macros

macro foo*(T: typedesc): typedesc =
  echo T.getTypeInst.treerepr
  echo "--------------------------------------"
  let instantiated = T.getTypeInst
  echo typeof instantiated.treeRepr[1]
  echo instantiated.treeRepr[1] # This is the char 'r'

  return getType(int)

type
  Task = ptr object
    prev, next: Task
    parent: Task
    fn: proc (param: pointer) {.nimcall.}
    # User data
    data: array[10, byte]

discard foo(typeof(default(Task)[]))

BracketExpr
  Sym "typeDesc"
  Sym "Task:ObjectType"
--------------------------------------
char
r

[ghost]

So instantiated[1] => T.getTypeInst[1] should return Sym "Task:ObjectType"

But that is not what you wrote: instantiated.treeRepr[1].
"BracketExpr..."[1] == 'r'

[mratsim]

guess I was lacking sleep, good catch.