if nil == X crashes the compiler

[PMunch]

Description

Fairly simple, passed some C code through c2nim and it spat out some if nil == X statements. These statements unfortunately crash the compiler with Error: internal error: getTypeDescAux(tyGenericParam) so figuring out what was wrong was a bit annoying. It works if typeof(X) is pointer, but crashes if it is for example ptr int.

Nim Version

Nim Compiler Version 2.0.4 [Linux: amd64]
Compiled at 2024-03-28
Copyright (c) 2006-2023 by Andreas Rumpf

git hash: b47747d
active boot switches: -d:release

Current Output

Error: internal error: getTypeDescAux(tyGenericParam)

Expected Output

Some kind of error message explaining that it can't infer the type.

Possible Solution

No response

Additional Information

var x: ptr int

if nil == x: # Crashes the compiler
  echo "X is nil!"

[metagn]

Same issue as #16148 (though this is only realized after 15 comments), related is #15154 but this is a simpler case of just proc foo[T](a, b: ptr T).

If nil is matching ptr T and resolving T to itself (i.e. T = T vs T = nil) or stopping the resolution of T in some other simple way then this should be fixable (isGeneric?), but if T is being resolved to int and the type of the nil parameter is not populated after the fact then this is a limitation and we need to detect if we assign an unresolved type to a position that won't be populated with resolved parameters later.

Very easy bandaid is:

proc `==`[T](a: typeof(nil) | typeof(nil), b: T) {.magic: "WhateverMagicPointerEqualityUses".}

but in general typeof(nil) | typeof(nil) is a hack and there is a chance this is easy to fix in the compiler.