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0 pointspmahoney10y ago0 comments

> they’re all tied to specific versions and you’d need a new package file to support a new version

I haven't looked at Spack, but as a Nix user, it's often the case that different versions of some software package require different packages in order to build them. For example, particularly on a less-used platform like darwin, I've submitted numerous patches to the Nix package of MariaDB due to minor breakages in newer versions. It's not always simple to parameterize the upstream version.

That said, there are many cases where it is that simple. Overriding a package in Nix to change the version is possible [1], but could be easier from a UX perspective.

> The user can install the version combination that you packaged, but can they easily try their own

As an example, I needed an older Ruby version that required an older libxml2 than available in nixpkgs. I did need to create my own Ruby package, but was able to simply override the version in the existing libxml2 package, and I configured nix to use that version across all other predefined nixpkgs that required libxml2 and were needed by my project. This meant a lot of compiling on my part (since nixpkgs of course can't publish binaries for my customized builds), but it was fairly straightforward.

[1] http://nixos.org/nixos/manual/index.html#sec-customising-pac...

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tgamblin10y ago

These are the things that Spack attempts to solve. If you look at slides 14-15 in the presentation above, the concretization process automates something like your second example. You can build with an arbitrary package version, e.g. `spack install ruby@1.8 ^libxml2@1.2`, and Spack will evaluate constraints on packages to build a new DAG. If some other dependency in the DAG says it can't build with the older libxml, or if the older libxml implies other dependency version constraints, they'll be integrated in the new DAG. The output of this process is a concrete specification, with all versions/compiler/variants/etc. filled in, which could be used to reproduce the build later.

If spack doesn't know about the version, it can try to scrape the package webpage to find it automatically, or you can just add another one-line `version()` directive in the package file, rather than creating a new package entirely or making a global config change.

My point is mainly that to automate this type of change, you need something like constraint solving to adjust the DAG. That can be used in conjunction with a functional Nix-like build, and actually adds some value to it. That is what Spack is doing. This is why I claim the constraint solving, etc., is not obsolete.

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tgamblin10y ago

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