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-rw-r--r--src/content/blog/2020/10/05/cargo2nix-demo.tar.gzbin59565 -> 0 bytes
-rw-r--r--src/content/blog/2020/10/05/cargo2nix.adoc72
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-rw-r--r--src/content/blog/2020/10/05/swift2nix-demo.tar.gzbin61691 -> 0 bytes
-rw-r--r--src/content/blog/2020/10/05/swift2nix.adoc194
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diff --git a/src/content/blog/2020/10/05/cargo2nix-demo.tar.gz b/src/content/blog/2020/10/05/cargo2nix-demo.tar.gz
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diff --git a/src/content/blog/2020/10/05/cargo2nix.adoc b/src/content/blog/2020/10/05/cargo2nix.adoc
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-= cargo2nix: Dramatically simpler Rust in Nix
-:sort: 1
-
-:empty:
-:swift2nix: link:swift2nix.html
-:cargo2nix: link:cargo2nix-demo.tar.gz
-
-In the same vein of my earlier post on {swift2nix}[swift2nix], I was able to
-quickly prototype a Rust and Cargo variation of it: {cargo2nix}[cargo2nix].
-
-The initial prototype is even smaller than swift2nix: it has only 37 lines of
-code.
-
-Here's how to use it (snippet taken from the repo's README):
-
-[source,nix]
-----
-let
- niv-sources = import ./nix/sources.nix;
- mozilla-overlay = import niv-sources.nixpkgs-mozilla;
- pkgs = import niv-sources.nixpkgs { overlays = [ mozilla-overlay ]; };
- src = pkgs.nix-gitignore.gitignoreSource [ ] ./.;
- cargo2nix = pkgs.callPackage niv-sources.cargo2nix {
- lockfile = ./Cargo.lock;
- };
-in pkgs.stdenv.mkDerivation {
- inherit src;
- name = "cargo-test";
- buildInputs = [ pkgs.latest.rustChannels.nightly.rust ];
- phases = [ "unpackPhase" "buildPhase" ];
- buildPhase = ''
- # Setup dependencies path to satisfy Cargo
- mkdir .cargo/
- ln -s ${cargo2nix.env.cargo-config} .cargo/config
- ln -s ${cargo2nix.env.vendor} vendor
-
- # Run the tests
- cargo test
- touch $out
- '';
-}
-----
-
-That `cargo test` part on line 20 is what I have been fighting with every
-"*2nix" available for Rust out there. I don't want to bash any of them. All I
-want is to have full control of what Cargo commands to run, and the "*2nix" tool
-should only setup the environment for me. Let me drive Cargo myself, no need to
-parameterize how the tool runs it for me, or even replicate its internal
-behaviour by calling the Rust compiler directly.
-
-Sure it doesn't support private registries or Git dependencies, but how much
-bigger does it has to be to support them? Also, it doesn't support those *yet*,
-there's no reason it can't be extended. I just haven't needed it yet, so I
-haven't added. Patches welcome.
-
-The layout of the `vendor/` directory is more explicit and public then what
-swift2nix does: it is whatever the command `cargo vendor` returns. However I
-haven't checked if the shape of the `.cargo-checksum.json` is specified, or
-internal to Cargo.
-
-Try out the demo (also taken from the repo's README):
-
-[source,sh]
-----
-pushd "$(mktemp -d)"
-wget -O- https://euandre.org/static/attachments/cargo2nix-demo.tar.gz |
- tar -xv
-cd cargo2nix-demo/
-nix-build
-----
-
-Report back if you wish.
diff --git a/src/content/blog/2020/10/05/cargo2nix.tar.gz b/src/content/blog/2020/10/05/cargo2nix.tar.gz
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diff --git a/src/content/blog/2020/10/05/swift2nix-demo.tar.gz b/src/content/blog/2020/10/05/swift2nix-demo.tar.gz
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diff --git a/src/content/blog/2020/10/05/swift2nix.adoc b/src/content/blog/2020/10/05/swift2nix.adoc
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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.
diff --git a/src/content/blog/2020/10/05/swift2nix.tar.gz b/src/content/blog/2020/10/05/swift2nix.tar.gz
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