Dne 03. 01. 23 v 4:30 Kevin Kofler via devel napsal(a):
Fabio Valentini wrote:- incompatible compile-time options (i.e. resulting in conditional compilation): different packages depend on crates with different sets of features enabled, sometimes with conflicting options. Even with a stable ABI, you'd need to build crates for all necessary combinations of configurations, and that matrix quickly explodes (i.e. usually exponentially - 2^n builds for for n independent flags). This is a deal-breaker for shared libraries in most cases, and also can't be solved by using a different compiler. (Unless you want to figure out *which* combinations to build, and *only* build these.)
I wish this was specific to Rust. We more or less deal with this issue in every ecosystem. We just sometimes choose to ignore the whole parts of the matrix, e.g. statically/dynamically linked libraries. But also support for some extensions, such as e.g. language bindings and what not. Or maybe platform support.
Let me try formulating my criticism more constructively (since my previous reply failed both at being polite and at getting my point through, sorry again for that): I am really surprised to read above that Rust apparently allows applications to pick the flag with which the libraries they depend on are compiled. I really have to wonder why anyone would think that allowing that would be a good idea, but then again I guess I know the answer: Whoever added this feature was so set in a mindset where everything is compiled on demand and statically linked that they figured: why not? And if you are in that mindset, that actually sounds like a reasonable call to make. Source-based software distributions do have the advantage of offering this kind of flexibility on demand, see also the USE flags in Gentoo. Those are in fact one of the main reasons some people decide to compile an entire GNU/Linux distribution from source (and hence pick a distribution such as Gentoo) to begin with. Likewise, the Rust way of compiling dependencies on demand allows applications to make this kind of settings for them. Still, I can see several issues with that approach, e.g., what if an application depends on two libraries A and B that both depend on library C, but with conflicting flags? But the main issue is that, as you point out, it makes binary distribution of shared libraries highly impractical. That is why I think this was a short-sighted design decision. But we will have to work around this one way or another, because I doubt anyone will be willing to remove that questionable feature now that developers have come to rely on it. (And no, I do not think the current Fedora approach of packaging crates in source form only is the optimal approach, for reasons I have already pointed out in other threads on this list.)
We don't need to remove this feature, just limit the scope into acceptable size.
Vít
I hope that the above now brings my point across constructively.
Kevin Kofler
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