Also, why is it immature for Rust to ship a toolchain and package manager through a sidechannel, but not Haskell?
Haskell also feels less mature to me than C, with fewer POSIX functions being readily available, but as mentioned above, with Haskell (in my experience; the experiences indeed seem to differ) it is "one or two dependencies have to be pulled from Hackage across multiple projects and system versions", while in Rust it is rather "I failed to pull common logging and argument parsing dependencies on a single up-to-date stable system, and apparently one is supposed to install and update its compiler, package manager, and libraries separately from the rest of the system". Though some use ghcup or Stack, which also aim working without a system package manager, but at least a system package manager is a viable option.
It just seems weird to blame Rust for a problem you had with your package manager, when every modern ecosystem I can think of eschews distro package managers because of these problems.
I also don't mean to blame Rust's ecosystem (let alone the language itself) in the sense of complaining about it, though talking about this feels that way, and I thought it might be useful to clarify: it appears to aim less "stable" and more "cutting edge" (or "experimental") versions and practices than "stable" system distributions do, and than more mature ecosystems tend to do. Likewise, I wouldn't call having a slightly older compiler version in system repositories a problem with package manager: this is a useful approach for getting a stable system, relatively well-tested and with predictable changes. Not every system has to be this way, but in some cases it is useful, some people (myself included) generally prefer those. And unfortunately those fail to play together smoothly at the moment, but I view it as an issue arising between those and their approaches, not as a problem of one of those.
In my mind, it's that updating a dependency doesn't break existing installations, or knowing that an existing install isn't going to get borked by an update.
And this is not something that is applicable to ecosystems like Rust, where it's not really possible to break a Rust program because another Rust program needs a newer version of the same dependency that happens to be incompatible with the older version. In fact, you can compile one Rust program that links against multiple versions of the same dependency at incompatible versions without issue.
So the entire notion of the Debian model of package management doesn't really apply to Rust, and there's not any benefit to keeping an older version of the toolchain around. There are only negatives.
And Rust has strong stability guarantees. A newer toolchain will not break compiles of older code. Nor will Cargo's cache break compiles with an existing lockfile because another package needed different incompatible versions of the same dependency. It's designed to be stable from first principles, in a way that C and C++ builds are not.
This is kind of why you're only going to have a bad time if you want to use the system package manager to manage your Rust packages. It's not built for the same problem domain, and over constrained for the design space.
