rls install fails with custom toolkits

[DavidGoodenough]

Trying to use the Espressiv build of the rust toolkits (which includes the Xtensa architecture and a tailored RISC-V for their ESP32 range) rls refuses to install complaining that "error: toolchain 'esp' does not support components: esp is a custom toolchain".

In rustup issue 1570 there is discussion that the rls installer is using the wrong technique to determine whether the components that RLS needs are installed. Could the installer be changed to use the techniques outlines in 1570?

Now I do not know if the Espressiv build does include the right components, but the error message does not tell me what (if anything) is missing, only that it can not find out what is there.