dev-lang/rust slots selection

[Skotlex]

Good day,
How do I filter which rust version slots I get? And how to know which versions I actually need?

I thought this would be automatically done by Portage's package dependency resolution... however, my latest emerge update world shows:

[Hu]

I am not involved in Gentoo's Rust maintenance, but from what I understand of Rust, this is unfortunately unsurprising. The Rust project is infamous for minimal compatibility, so if you want to build rust-1.81, you need rust-1.80 to do it. rust-1.79 officially does not suffice; it may or may not work, but is not considered supported. Thus, you need rust-1.80 too, so that you can build rust-1.81. Since you don't have rust-1.80, you need rust-1.79 so that you can build rust-1.80. The chain progresses from there. I think it only cuts off because Gentoo does not have packages to let you continue all the way back to the OCaml-based Rust from the dawn of time.

On the positive side, if you obtain a prebuilt rust built by a trusted source, that will not require you to have the immediately preceding version of rust in order to install it. Portage appears to eventually fall back on this, when it needs a =rust-1.73 or >=rust-bin-1.73, cannot find the former, and so uses rust-bin-1.74 in order to build rust-1.74. Presumably, forcing Portage to install a very current rust-bin would truncate the chain.

What on your system requires any version of Rust, other than Rust itself?

[bstaletic]

This happens because dev-lang/rust-1.82 can only be compiled by an already installed dev-lang/rust-1.82, or dev-lang/rust-1.81 (or the dev-lang/rust-bin of the same version).
This creates a chain until you hit a missing dev-lang/rust version and portage decides to pick rust-bin for the missing version.

Alternative is to decide on a version and install rust-bin.
If you really want to compile that version, without compiling all previous versions, grab the rust-bin variant, without recording it in your world file. Then compile the same version from source.

[Skotlex]

It would had been really useful to have Portage tell me instead of... well, this. Thanks for the heads-up, this will spare me a lot of compiling time :)

EDIT: The curious bit is I already have installed:

[Skotlex]

[bstaletic]