39 lines
1.5 KiB
Markdown
39 lines
1.5 KiB
Markdown
# pkgs.checkpointBuildTools {#sec-checkpoint-build}
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`pkgs.checkpointBuildTools` provides a way to build derivations incrementally. It consists of two functions to make checkpoint builds using Nix possible.
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For hermeticity, Nix derivations do not allow any state to be carried over between builds, making a transparent incremental build within a derivation impossible.
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However, we can tell Nix explicitly what the previous build state was, by representing that previous state as a derivation output. This allows the passed build state to be used for an incremental build.
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To change a normal derivation to a checkpoint based build, these steps must be taken:
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- apply `prepareCheckpointBuild` on the desired derivation, e.g.
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```nix
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checkpointArtifacts = (pkgs.checkpointBuildTools.prepareCheckpointBuild pkgs.virtualbox);
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```
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- change something you want in the sources of the package, e.g. use a source override:
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```nix
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changedVBox = pkgs.virtualbox.overrideAttrs (old: {
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src = path/to/vbox/sources;
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});
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```
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- use `mkCheckpointBuild changedVBox checkpointArtifacts`
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- enjoy shorter build times
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## Example {#sec-checkpoint-build-example}
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```nix
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{ pkgs ? import <nixpkgs> {} }:
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let
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inherit (pkgs.checkpointBuildTools)
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prepareCheckpointBuild
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mkCheckpointBuild
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;
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helloCheckpoint = prepareCheckpointBuild pkgs.hello;
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changedHello = pkgs.hello.overrideAttrs (_: {
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doCheck = false;
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patchPhase = ''
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sed -i 's/Hello, world!/Hello, Nix!/g' src/hello.c
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'';
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});
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in mkCheckpointBuild changedHello helloCheckpoint
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```
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