I tried to use Rust for a tiny microcontroller (GD32VF103, 128KB flash).

First of all, I was amazed by how much I could do with Rust (safe Rust, even), and how well it was interfacing with my handwritten RISC-V assembly. I will definitely use Rust again for the next such project.

But, every time my functions would get over a certain size, suddenly some optimizations stopped working, and Rust was trying to put the whole panic/fmt machinery into the thing, going above my linker's flash size limit. It was insanely frustrating, since there was no rhyme or reason to it. Simply adding another branch to a match made it do that. Or another if statement that was exactly the same as the 4 before it.

The 137 binary thing does not scale.