A full rust compiler instead of use the "de facto" one? on a language as complicated as rust that sounds scary unless they have a lot of financial backing and significant amount of compiler devs.

Why would they not just adapt the code generator for the reference compiler? Rust is a moving target, committing to a new compiler at this point is a massive investment.

Not a rust compiler, they provide crates to interface with their C code in ESP-IDF, which is essentially a FreeRTOS port that supports the dual core Espressif chips, which vanilla FreeRTOS does not support. Also some of their own libraries for things like MQTT, which I found unfortunately subpar in comparison to the vanilla FreeRTOS code.

It’s all beta software, but here is what they list in the docs:

Services like Wi-Fi, HTTP client/server, MQTT, OTA updates, logging etc. are exposed via Espressif's open source IoT Development Framework, ESP-IDF. It is mostly written in C and as such is exposed to Rust in the canonical split crate style:

a sys crate to provide the actual unsafe bindings (esp-idf-sys) a higher level crate offering safe and comfortable Rust abstractions (esp-idf-svc) The final piece of the puzzle is low-level hardware access, which is again provided in a split fashion:

esp-idf-hal implements the hardware-independent embedded-hal traits like analog/digital conversion, digital I/O pins, or SPI communication - as the name suggests, it also uses ESP-IDF as a foundation if direct register manipulation is required, esp32c3 provides the peripheral access crate generated by svd2rust. More information is available in the ecosystem chapter of The Rust on ESP Book.