importcpp + CRTP: Compiler exit without output or errors

[mratsim]

Nim supports CRTP (Curiously recurring template pattern) in its type system:

type
  Example*{.bycopy.}[Data, Target] = object
    data*: Data
    target*: Target

  BatchDataset*{.bycopy, pure, inheritable.} = object

  Dataset*{.bycopy, pure.}[Self, Batch] = object of BatchDataset

  Mnist*{.bycopy, pure.} = object of Dataset[Mnist, seq[Example[float64, float64]]]

func mnist(rootPath: cstring): Mnist =
  discard

let m = mnist("path/to/mnist")
echo "Success"
echo m

but when this is used for C++ bindings, the compiler exits without producing code or errors, there is not even a nimcache folder created.

type
  Example*{.bycopy, importcpp: "torch::data::Example".}[Data, Target] = object
    data*: Data
    target*: Target

  BatchDataset*{.bycopy, pure, inheritable,
    importcpp: "torch::data::datasets::BatchDataset".}
    = object

  Dataset*{.bycopy, pure,
    importcpp: "torch::data::datasets::Dataset".}[Self, Batch]
    = object of BatchDataset

  Mnist*{.bycopy, pure,
    importcpp: "torch::data::datasets::MNIST".}
    = object of Dataset[Mnist, seq[Example[float64, float64]]]

func mnist(rootPath: cstring): Mnist =
  discard

let m = mnist("path/to/mnist")
echo "Success"
echo m

Note: obviously the C++ compiler will refuse to compile since you don't have the header and DLL, but it shouldn't exit silently at the Nim level.