Avoid full rebuild

alitvak69 · April 8, 2021, 4:33am

Sorry for a newb question. I just starting using nix to build static podman from source. I ran this:

curl -L https://nixos.org/nix/install | sh

git clone GitHub - containers/podman: Podman: A tool for managing OCI containers and pods. && cd podman

nix build -f nix/

I got a successful build of the master binary.

Then I checkout a released version:

git checkout v3.1.0

And finally ran

nix build -f nix/

It looked to me like nix started building all of the packages from scratch and I had 28 i.e. 27 + podman.

I expected that all other dependencies should be cached because a new build started right after the 1st one completed.

I tried looking into documentation but couldn’t find any clues

the 2nd build in the process looks like 1/19/28, shouldn’t rebuild be like 2/x/x ?

Any clues are appreciated,

j-k · April 8, 2021, 6:51am

The source provided to the derivation is different so it requires a full rebuild in order to be reproducible.

danieldk · April 8, 2021, 6:52am

master and 3.1.0 use different pinned versions of nixpkgs:

github.com

containers/podman/blob/9ba2e78cdcc28c15d72a76f6200a74e7ad6562b1/nix/nixpkgs.json

{
  "url": "https://github.com/nixos/nixpkgs",
  "rev": "42a03e4728fc05cb9f123057670e41967f628360",
  "date": "2021-04-02T23:08:32+02:00",
  "path": "/nix/store/d1vqa0kpa69zzcaj5kqgkmrxr3s7vli1-nixpkgs",
  "sha256": "0wrn5nayxckj11z2qlvsya2lzssbccbk50llxmgdm0qb5y14shfk",
  "fetchSubmodules": false,
  "deepClone": false,
  "leaveDotGit": false
}

github.com

containers/podman/blob/9f09fb62cba8f44c18eda84db3e72aab3ae76046/nix/nixpkgs.json

{
  "url": "https://github.com/nixos/nixpkgs",
  "rev": "f38b9b258f3f4db5ecf7dd27a7d5b48f23202843",
  "date": "2021-03-07T14:22:16+01:00",
  "path": "/nix/store/df3v1b2qfsbnsd6fwaw4787qdy5rcxkc-nixpkgs",
  "sha256": "1dbi7rjyfkv3rw6zqwbc6jknbdgyv16cd8zgcpq5gdj0mwnp9b13",
  "fetchSubmodules": false,
  "deepClone": false,
  "leaveDotGit": false
}

So, given that many dependencies have probably changed, it’s expected that different output paths are fetched from the cache and packages are rebuilt.