Error: 'auto' parameter not permitted in this context when using extended lambda in body of auto template function

Accelerated Computing CUDA CUDA NVCC Compiler
1

Trying to make use of some C++20 features in my code, I stumbled across the following behavior:

int foo(auto a)
{
    auto x = [] __device__ __host__ (int b)
    {
        return b;
    };
    return x(a);
}

int main()
{
    return foo(2);
}

This code results in a compiler error (Godbolt link):

<source>: In function 'int foo(auto:11)':
<source>:3:70: error: 'auto' parameter not permitted in this context
    3 |     auto x = [] __device__ __host__ (int b)
      |                                                                      ^   
<source>:3:86: error: invalid use of 'auto' in template argument
    3 |     auto x = [] __device__ __host__ (int b)
      |                                                                                      ^
<source>:3:97: error: template argument 2 is invalid
    3 |     auto x = [] __device__ __host__ (int b)
      |                                                                                                 ^
<source>:3:99: error: template argument 3 is invalid
    3 |     auto x = [] __device__ __host__ (int b)
      |                                                                                                   ^
ASM generation compiler returned: 1
<source>: In function 'int foo(auto:11)':
<source>:3:70: error: 'auto' parameter not permitted in this context
    3 |     auto x = [] __device__ __host__ (int b)
      |                                                                      ^   
<source>:3:86: error: invalid use of 'auto' in template argument
    3 |     auto x = [] __device__ __host__ (int b)
      |                                                                                      ^
<source>:3:97: error: template argument 2 is invalid
    3 |     auto x = [] __device__ __host__ (int b)
      |                                                                                                 ^
<source>:3:99: error: template argument 3 is invalid
    3 |     auto x = [] __device__ __host__ (int b)
      |                                                                                                   ^
Execution build compiler returned: 1

Is this a limitation of extended lambdas, or a bug in nvcc? If this is a limitation, I assume it is similar to this case here:

int main()
{
    auto foo = [](auto a)
    {
        auto x = [] __device__ __host__ (int b)
        {
            return b;
        };
        return x(a);
    };

    return foo(2);
}

which results in (Godbolt):

<source>(5): error: An extended __host__ __device__ lambda cannot be defined inside a generic lambda expression("operator()").

1 error detected in the compilation of "<source>".
ASM generation compiler returned: 2
<source>(5): error: An extended __host__ __device__ lambda cannot be defined inside a generic lambda expression("operator()").

1 error detected in the compilation of "<source>".
Execution build compiler returned: 2

In that case, it would be nice to have a similarly descriptive error message, as opposed to the current one.