Background: I just submitted some patches for some crates, setting #:skip-build for those I touched or added. My rational:

1) Building crate "libraries" is of no use. Rust still has no notion of "libraries", neither shared not static. it does not even provide any means to use "object"-files from another package. All crates will be build again and again for each package using it. And you will notice that the output of most crates will be almost empty (only exception: if the crate build a program).

2) This is what the crates importer does: It sets skip-build for all packages it imports as dependencies. It also does not add the crate-build-dependencies for these packages. (Please note that while I made the crates importer to honor semver versions, this has already been prepared in other patches and was not argued about.

Am 17.12.20 um 21:08 schrieb Efraim Flashner:

When I started packaging crates, I did this too. But then I learned, that others do not. So we should define how this should be handled in the future - and adjust the importer accordingly.

This might not be possible - as there is another issue in the Rust ecosystem: The language is still moving fast.

3) If some packages requires rustc 1.46, while our default rustc is still 1.40, we need to add rustc-1.46 as an input to this package and to many of it's dependents. (AFAIR the package will even depend on *both* version then.) Now if we move on to rustc 1.50, extra care has to be taken to remove these dependencies.

Even worse: All packages depending on such a package on will also depend on rustc 1.46, and all changes to rustc 1.46 will trigger a rebuild - without *any* use.

4) Since (2) building rust packages costs *a lot* of resources: time, memory and electrical power. As an example, building sequoia takes about 20 Minutes on my machine. Most of the time is spend compiling dependencies of dependencies. And all these dependencies of dependencies will be compiled over and over again.

5) *If* we decide to build dependencies, we should restrict this to *one* build. This means: either not run the tests or only do a test build. The reason is: When running the tests, all the code, including the dependencies, is compiled again with some "test" flag set. This will add yet another huge amount of time, memory and electrical power.

To give you some figure: A release and test build for sequoia takes about 45 minutes on my machine, requiring 9 GB of space in /tmp. So this is double the time if the release build only.

I can't imaging how many hours it would take to rebuild sequoia is one of the lower level dependencies changes - which is quite often the case in rust.

6) This not only effect berlin, but also every user out there requiring a rebuild for some reason. This will lead to a very, very bad user experience - practically kicking out users with less powerful equipment.

7) Given the rushing climate crisis, we MUST NOT waste this gigantic amount of electrical power. We are in a position of huge impact. If we decide to save power, hundreds of Guix users will save power (and money). If we decide to waste power, this will multiply by the number of Guix users.