From 020c1e77489b772f854bb3288b9c8d2818a6bf9d Mon Sep 17 00:00:00 2001
From: EuAndreh <eu@euandre.org>
Date: Fri, 18 Apr 2025 02:17:12 -0300
Subject: git mv src/content/* src/content/en/

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-= swift2nix: Run Swift inside Nix builds
-:sort: 0
-
-:empty:
-:nix: https://nixos.org/
-:swift2nix: link:swift2nix.tar.gz
-
-While working on a Swift project, I didn't find any tool that would allow Swift
-to run inside {nix}[Nix] builds.  Even thought you _can_ run Swift, the real
-problem arises when using the package manager.  It has many of the same problems
-that other package managers have when trying to integrate with Nix, more on this
-below.
-
-I wrote a simple little tool called {swift2nix}[swift2nix] that allows you trick
-Swift's package manager into assuming everything is set up.  Here's the example
-from swift2nix's README file:
-
-[source,nix]
-----
-let
-  niv-sources = import ./nix/sources.nix;
-  pkgs = import niv-sources.nixpkgs { };
-  src = pkgs.nix-gitignore.gitignoreSource [ ] ./.;
-  swift2nix = pkgs.callPackage niv-sources.swift2nix {
-    package-resolved = ./Package.resolved;
-  };
-in pkgs.stdenv.mkDerivation {
-  inherit src;
-  name = "swift-test";
-  buildInputs = with pkgs; [ swift ];
-  phases = [ "unpackPhase" "buildPhase" ];
-  buildPhase = ''
-    # Setup dependencies path to satisfy SwiftPM
-    mkdir .build
-    ln -s ${swift2nix.env.dependencies-state-json} .build/dependencies-state.json
-    ln -s ${swift2nix.env.checkouts} .build/checkouts
-
-    # Run the tests
-    swift test
-    touch $out
-  '';
-}
-----
-
-The key parts are lines 15~17: we just fake enough files inside `.build/` that
-Swift believes it has already downloaded and checked-out all dependencies, and
-just moves on to building them.
-
-I've worked on it just enough to make it usable for myself, so beware of
-unimplemented cases.
-
-== Design
-
-What swift2nix does is just provide you with the bare minimum that Swift
-requires, and readily get out of the way:
-
-. I explicitly did not want to generated a `Package.nix` file, since
-  `Package.resolved` already exists and contains the required information;
-. I didn't want to have an "easy" interface right out of the gate, after
-  fighting with "*2nix" tools that focus too much on that.
-
-The final actual code was so small (46 lines) that it made me think about
-package managers, "*2nix" tools and some problems with many of them.
-
-== Problems with package managers
-
-I'm going to talk about solely language package managers.  Think npm and cargo,
-not apt-get.
-
-Package managers want to do too much, or assume too much, or just want to take
-control of the entire build of the dependencies.
-
-This is a recurrent problem in package managers, but I don't see it as an
-intrinsic one.  There's nothing about a "package manager" that prevents it from
-_declaring_ what it expects to encounter and in which format.  The _declaring_
-part is important: it should be data, not code, otherwise you're back in the
-same problem, just like lockfiles are just data.  Those work in any language,
-and tools can cooperate happily.
-
-There's no need for this declarative expectation to be standardized, or be made
-compatible across languages.  That would lead to a poor format that no package
-manager really likes.  Instead, If every package manager could say out loud what
-it wants to see exactly, than more tools like swift2nix could exist, and they
-would be more reliable.
-
-This could even work fully offline, and be simply a mapping from the lockfile
-(the `Package.resolved` in Swift's case) to the filesystem representation.  For
-Swift, the `.build/dependencies-state.json` comes very close, but it is internal
-to the package manager.
-
-Even though this pain only exists when trying to use Swift inside Nix, it sheds
-light into this common implicit coupling that package managers have.  They
-usually have fuzzy boundaries and tight coupling between:
-
-. resolving the dependency tree and using some heuristic to pick a package
-  version;
-. generating a lockfile with the exact pinned versions;
-. downloading the dependencies present on the lockfile into some local cache;
-. arranging the dependencies from the cache in a meaningful way for itself
-  inside the project;
-. work using the dependencies while _assuming_ that step 4 was done.
-
-When you run `npm install` in a repository with no lockfile, it does 1~4.  If
-you do the same with `cargo build`, it does 1~5.  That's too much: many of those
-assumptions are implicit and internal to the package manager, and if you ever
-need to rearrange them, you're on your own.  Even though you can perform some of
-those steps, you can't compose or rearrange them.
-
-Instead a much saner approach could be:
-
-. this stays the same;
-. this also stays the same;
-. be able to generate some JSON/TOML/edn which represents the local expected
-  filesystem layout with dependencies (i.e. exposing what the package manager
-  expects to find), let's call it `local-registry.json`;
-. if a `local-registry.json` was provided, do a build using that.  Otherwise
-  generate its own, by downloading the dependencies, arranging them, _etc._
-
-The point is just making what the package manager requires visible to the
-outside world via some declarative data.  If this data wasn't provided, it can
-move on to doing its own automatic things.
-
-By making the expectation explicit and public, one can plug tools _à la carte_
-if desired, but doesn't prevent the default code path of doing things the exact
-same way they are now.
-
-== Problems with "*2nix" tools
-
-:node2nix: https://github.com/svanderburg/node2nix
-
-I have to admit: I'm unhappy with most of they.
-
-They conflate "using Nix" with "replicating every command of the package manager
-inside Nix".
-
-The avoidance of an "easy" interface that I mentioned above comes from me
-fighting with some of the "*2nix" tools much like I have to fight with package
-managers: I don't want to offload all build responsibilities to the "*2nix"
-tool, I just want to let it download some of the dependencies and get out of the
-way.  I want to stick with `npm test` or `cargo build`, and Nix should only
-provide the environment.
-
-This is something that {node2nix}[node2nix] does right.  It allows you to build
-the Node.js environment to satisfy NPM, and you can keep using NPM for
-everything else:
-
-[source,sh]
-----
-ln -s ${node2nix-package.shell.nodeDependencies}/lib/node_modules ./node_modules
-npm test
-----
-
-Its natural to want to put as much things into Nix as possible to benefit from
-Nix's advantages.  Isn't that how NixOS itself was born?
-
-But a "*2nix" tool should leverage Nix, not be coupled with it.  The above
-example lets you run any arbitrary NPM command while profiting from isolation
-and reproducibility that Nix provides.  It is even less brittle: any changes to
-how NPM runs some things will be future-compatible, since node2nix isn't trying
-to replicate what NPM does, or fiddling with NPM's internal.
-
-**A "*2nix" tool should build the environment, preferably from the lockfile
-directly and offload everything else to the package manager**.  The rest is just
-nice-to-have.
-
-swift2nix itself could provide an "easy" interface, something that allows you to
-write:
-
-[source,sh]
-----
-nix-build -A swift2nix.release
-nix-build -A swift2nix.test
-----
-
-The implementation of those would be obvious: create a new
-`pkgs.stdenv.mkDerivation` and call `swift build -c release` and `swift test`
-while using `swift2nix.env` under the hood.
-
-== Conclusion
-
-Package managers should provide exact dependencies via a data representation,
-i.e. lockfiles, and expose via another data representation how they expect those
-dependencies to appear on the filesystem, i.e. `local-registry.json`.  This
-allows package managers to provide an API so that external tools can create
-mirrors, offline builds, other registries, isolated builds, _etc._
-
-"*2nix" tools should build simple functions that leverage that
-`local-registry.json`{empty}footnote:local-registry[
-  This `local-registry.json` file doesn't have to be checked-in the repository
-  at all.  It could be always generated on the fly, much like how Swift's
-  `dependencies-state.json` is.
-] data and offload all the rest back to the package manager itself.  This allows
-the "*2nix" to not keep chasing the package manager evolution, always trying to
-duplicate its behaviour.
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