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42 lines
1.4 KiB
Markdown
42 lines
1.4 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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```nix
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{
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checkpointArtifacts = (pkgs.checkpointBuildTools.prepareCheckpointBuild pkgs.virtualbox);
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}
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```
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```nix
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{
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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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```
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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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{
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pkgs ? import <nixpkgs> { },
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}:
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let
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inherit (pkgs.checkpointBuildTools) prepareCheckpointBuild mkCheckpointBuild;
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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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postPatch = ''
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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
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mkCheckpointBuild changedHello helloCheckpoint
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```
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