SIGSEGV on generic macro returning a type

[Quelklef]

The following SIGSEGVs:

macro f(x: static[int]): untyped = discard
proc g[X: static[int]](v: f(X)) = discard

This is valid with the type system, though, right? Since X is known at compile-time it can be used to generate a type for v? I want to do something like this:

type MyFancyConcreteType = ...
type MyFancyGenericType[N: static[int]] = ...

macro Choose(N: static[int]): untyped =
  if N == 2:
    return ident("MyFancyConcreteType")
  else:
    return nnkBracketExpr.newTree(ident("MyFancyGenericType"), newIntLitNode(N))

var x: Choose(2)  # of MyFancyConcreteType
var y: Choose(3)  # of MyFancyGenericType[3]

# Generic procs may still be written
proc doSomethingWithEither[N: static[int]](v: Choose(N)) = ...

Is this possible, SIGSEGV or no; should I abandon the idea?

[Quelklef]

I should also not that this is a static[T] issue; the following compiles fine (but does not "work"):

import macros

macro f(x: untyped): untyped =
  newIdentNode("int")

proc g[X](x: f(X)) =
  discard

[mratsim]

I don't know if it should work or not.

At the moment you can generate the proc in the macro or use a wrapper type like I did in Stint.

In you example that would be something like this:

macro Choose(N: static[int]): untyped =
  if N == 2:
    return ident("MyFancyConcreteType")
  else:
    return nnkBracketExpr.newTree(ident("MyFancyGenericType"), newIntLitNode(N))

type MyFancyConcreteType = ...
type MyFancyGenericType[N: static[int]] = ...

type MyFancyType[N: static[int]] = object
  impl: Choose[N]

var x: Choose(2)  # of MyFancyConcreteType
var y: Choose(3)  # of MyFancyGenericType[3]

# Generic procs may still be written
proc doSomethingWithEither[N: static[int]](v: MyFancyType[N]) = ...

You should put a full working example, btw. I think your issue is linked to #7231

[Quelklef]

Yes, I believe you helped me implement your solution a while back. I decided I wanted to see if I could find a solution involving no wrapper types.

What do you mean by a full working example? In regards to the bug, or to my intended feature?

[mratsim]

I meant:

type MyFancyConcreteType = object
type MyFancyGenericType[N: static[int]] = object
  foo: array[N, int]

Instead of type MyFancyConcreteType = ... so that we can directly copy-paste like the lazy programmers we are :).

[Quelklef]

Ah, I'll be sure to keep that in mind for the future ;-)

[saem]

Tested in playground, no more sigsev, an error is produced instead: /usercode/in.nim(2, 28) Error: expression '' has no type (or is ambiguous)

[metagn]

Early generic evaluation bug again, can link #8551 and #22607 right now but there are more related issues

As described in the other issues, delegating to a generic type is a workaround

macro f(x: static[int]): untyped = discard
type FWrapper[x: static int] = f(x)
proc g[X: static[int]](v: FWrapper[X]) = discard