When implementing a Terraform provider, for one. At one point I had the scaffolding up to build providers in Rust (contributing to Tonic and Rusoto along the way) - many of the bugs in TF providers would be resolved by generics and type safety.

> When is it actually desirable to imperatively program your cloud provider rather than using something like Terraform?

One place I've done is when your infra needs to dynamically scale up/down based on load.

TF supports this just fine

I have built several services that do dynamic infrastructure provisioning in response to API calls as part of the core functionality. This isn’t unusual.

Even if I wanted to use real programming language for that, Pulumi seems to be better choice.

It's not, trust me. Use the terraform CDK instead.

Maybe this makes it easier to develop things like Terraform using Rust?