gistfile1.nim

{.emit:"""

struct FooBase {
    int x;
};

template <typename T>
struct Foo: FooBase {
    T val;
};

""".}

type
    FooBase*{.importcpp, inheritable.} = object
    Foo*{.importcpp.}[T] = object of FooBase
        val*: T

var f1: FooBase # fine
var f2: Foo[int] # causes error:
# testcpp.nim(17, 8) Error: internal error: mangleRecFieldName