pyrox.dev
1# pkgs.checkpointBuildTools {#sec-checkpoint-build}
2
3`pkgs.checkpointBuildTools` provides a way to build derivations incrementally. It consists of two functions to make checkpoint builds using Nix possible.
4
5For hermeticity, Nix derivations do not allow any state to be carried over between builds, making a transparent incremental build within a derivation impossible.
6
7However, 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.
8
9To change a normal derivation to a checkpoint based build, these steps must be taken:
10 - apply `prepareCheckpointBuild` on the desired derivation, e.g.
11```nix
12{
13 checkpointArtifacts = (pkgs.checkpointBuildTools.prepareCheckpointBuild pkgs.virtualbox);
14}
15```
16 - change something you want in the sources of the package, e.g. use a source override:
17```nix
18{
19 changedVBox = pkgs.virtualbox.overrideAttrs (old: {
20 src = path/to/vbox/sources;
21 });
22}
23```
24 - use `mkCheckpointBuild changedVBox checkpointArtifacts`
25 - enjoy shorter build times
26
27## Example {#sec-checkpoint-build-example}
28```nix
29{
30 pkgs ? import <nixpkgs> { },
31}:
32let
33 inherit (pkgs.checkpointBuildTools)
34 prepareCheckpointBuild
35 mkCheckpointBuild
36 ;
37 helloCheckpoint = prepareCheckpointBuild pkgs.hello;
38 changedHello = pkgs.hello.overrideAttrs (_: {
39 doCheck = false;
40 patchPhase = ''
41 sed -i 's/Hello, world!/Hello, Nix!/g' src/hello.c
42 '';
43 });
44in
45mkCheckpointBuild changedHello helloCheckpoint
46```