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# Demonstration of incremental builds for Haskell. Useful for speeding up CI.
#
# See: https://www.haskellforall.com/2022/12/nixpkgs-support-for-incremental-haskell.html
# See: https://felixspringer.xyz/homepage/blog/incrementalHaskellBuildsWithNix
{ haskell, lib }:
let
inherit (haskell.lib.compose) overrideCabal;
# Incremental builds work with GHC >=9.4.
temporary = haskell.packages.ghc944.temporary;
# This will do a full build of `temporary`, while writing the intermediate build products
# (compiled modules, etc.) to the `intermediates` output.
temporary-full-build-with-incremental-output = overrideCabal (drv: {
doInstallIntermediates = true;
enableSeparateIntermediatesOutput = true;
}) temporary;
# This will do an incremental build of `temporary` by copying the previously
# compiled modules and intermediate build products into the source tree
# before running the build.
#
# GHC will then naturally pick up and reuse these products, making this build
# complete much more quickly than the previous one.
temporary-incremental-build = overrideCabal (drv: {
previousIntermediates = temporary-full-build-with-incremental-output.intermediates;
}) temporary;
in
temporary-incremental-build.overrideAttrs (old: {
meta = {
maintainers = lib.teams.mercury.members;
};
})
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