getTypeInst for generics does not gives the full instantiation info in certain cases

[mratsim]

Another case of difficulties working with types #7719/nim-lang/RFCs#44 and subtypes #6454 in macros.

In the following case I am trying to extract a subtype of multiple containers. It works fine for the built-in seq but not for a generic type. The subtype is not available through getTypeInst.

import macros, typetraits, sequtils

type
  CustomSeq*[T] = object
    data*: seq[T]

proc getSubType*(T: NimNode): NimNode =
  echo getTypeInst(T).treerepr
  result = getTypeInst(T)[1]

macro typed_helper(x: varargs[typed]): untyped =
  let foo = getSubType(x[0])

  result = quote do: discard

macro untyped_heavylifting(x: varargs[untyped]): untyped =

  var containers = nnkArgList.newTree()

  for arg in x:
    case arg.kind:
    of nnkInfix:
      if eqIdent(arg[0], "in"):
        containers.add arg[2]
    else:
      discard

  result = quote do:
    typed_helper(`containers`)

var a, b, c: seq[int]

untyped_heavylifting z in c, x in a, y in b:
  discard

## The following gives me CustomSeq instead
## of CustomSeq[int] in getTypeInst
var u, v, w: CustomSeq[int]

untyped_heavylifting z in u, x in v, y in w:
  discard

[krux02]

The example is a bit verbose, I could boil it a bit down if that helps to fix the bug. It seems like varargs is causing the problem, because without varargs, it just works.

import macros

type
  CustomSeq*[T] = object
    data*: seq[T]

# when using just one argument, `foo` and `bar` should be exactly
# identical.
macro foo(arg: typed): untyped =
  echo arg.getTypeInst.treeRepr

macro bar(args: varargs[typed]): untyped =
  for arg in args:
    echo arg.getTypeInst.treeRepr

var
  a: seq[int]
  b: Custoimport macros

type
  CustomSeq*[T] = object
    data*: seq[T]

# when using just one argument, `foo` and `bar` should be exactly
# identical.
macro foo(arg: typed): untyped =
  echo arg.getTypeInst.treeRepr

macro bar(args: varargs[typed]): untyped =
  for arg in args:
    echo arg.getTypeInst.treeRepr

var
  a: seq[int]
  b: CustomSeq[int]

# these two should print the exact same
foo(a) # prints seq[int], OK
bar(a) # prints seq[int], OK

foo(b) # prints CustomSeq[int], OK
# The following prints `CustomSeq` instead of `CustomSeq[int]`.
bar(b) # prints CustomSeq     , Wrong
mSeq[int]

# these two should print the exact same
foo(a) # prints seq[int], OK
bar(a) # prints seq[int], OK

foo(b) # prints CustomSeq[int], OK
# The following prints `CustomSeq` instead of `CustomSeq[int]`.
bar(b) # prints CustomSeq     , Wrong

@mratsim as a workaround of the broken varargs you could write lots of overloads until varargs[typed] will work again.

macro typed_helper(arg1: typed): untyped = #[ ... ]#
macro typed_helper(arg1,arg2: typed): untyped = #[ ... ]#
macro typed_helper(arg1,arg2,arg3: typed): untyped = #[ ... ]#
macro typed_helper(arg1,arg2,arg3,arg4: typed): untyped = #[ ... ]#
...

[LemonBoy]

The problem (?) is here, I don't know much about the sigmatch internals to suggest a solution though.