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John A. Lotoski
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91 lines
2.9 KiB
Markdown
91 lines
2.9 KiB
Markdown
# Developer Architecture Overview
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This shall give a sufficiently good overview over the haskell.nix
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ideas, such that a new developer can navigate around without too
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much trouble.
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## Packages
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`haskell.nix` is centered around packages (haskell package
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descriptions as nix-expressions). These are generated by
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`cabal-to-nix` from the `nix-tools` package. `stack-to-nix` and
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`plan-to-nix` will delegate the transformation of cabal packages to
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nix expressions to the same code that `cabal-to-nix` uses.
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These packages will look similar to the following:
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```nix
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{ system, compiler, flags, pkgs, hsPkgs, pkgconfPkgs, ... }:
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{
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flags = {};
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package = { ... };
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components = {
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"library" = { depends = [ ... ]; };
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exes = { "..." = { depends = [ ... ]; }; ... };
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sublibs = { "..." = { depends = [ ... ]; }; ... };
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tests = { "..." = { depends = [ ... ]; }; ... };
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benchmarks = { "..." = { depends = [ ... ]; }; ... };
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};
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};
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```
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The exact specification can be found in `modules/package.nix`.
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## Plans
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Packages (unless specified directly in the `packages` attribute of the
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module) usually come from a plan. A plan is either a Stackage snapshot
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(nightly or LTS) or a build plan as produced by `cabal`.
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Plan files usually look like the following:
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```nix
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hackage:
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{
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packages = {
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"$pkg".revision = hackage.$pkg.$version.revisions.default;
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"$pkg".flags = { flag1 = true; flag2 = false; ... };
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...
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};
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compiler = {
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version = "8.4.4";
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nix-name = "ghc844";
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packages = {
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"binary" = "0.8.5.1";
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...
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};
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};
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}
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```
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This provides enough information about the compiler, what packages the
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compiler ships with and the packages we want to use in our plan.
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This revision and flag information will be inlined into a list of
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packages in `config.packages` in `modules/plan.nix`. Thus
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`config.packages` will only contains packages as described in the
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previous section.
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## Package Sets (of derivations)
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We finally tie this all together in `package-set.nix` where we use
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`modules/component-driver.nix` to produce the derivations for each
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packages component to produce the final `config.hsPkgs` value.
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There is also a `modules/compat-driver.nix` that should produce the
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same packageset to be used with the stock haskell infrastructure in
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nixpkgs (*This has undergone substantially less testing*).
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### Component builder
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To prevent depending on multiple instances of the same libraries, the
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component builder will try to build every package from scratch and
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rely as little as possible on packages that are shipped with the GHC
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distribution. The exceptions are packages that are known to not be
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reinstallable. See `config.nonReinstallablePkgs`.
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The component builder can be found in `modules/component-driver.nix`
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and `builder/default.nix`. The component-driver will ensure that we do
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not try to rebuild non-reinstallable packages, and call the
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`builder/default.nix` on each package in `config.packages` to produce
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`config.hsPkgs`.
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