How can I add rustfmt to rust with html ?

[YievCkim]

Hello I switched on this (mode)[https://github.com/rayliwell/rstml-ts-mode] in order to edit source file combining rust and html. I am trying to setup format-all for this. But it seems the language is not recognized as Rust and format-all fails with this error:

format-all--prompt-for-formatter: No supported formatters for this language

What is the language name I am supposed to register into format-all configuration ? How can I know it ?