document post-build-hook usage

[domenkozar]

       post-build-hook
           Optional. The path to a program to execute after each build.

           This option is only settable in the global nix.conf, or on the command line by trusted users.

           When using the nix-daemon, the daemon executes the hook as root. If the nix-daemon is not involved, the hook runs as the user executing the nix-build.

           ·   The hook executes after an evaluation-time build.

           ·   The hook does not execute on substituted paths.

           ·   The hook's output always goes to the user's terminal.

           ·   If the hook fails, the build succeeds but no further builds execute.

           ·   The hook executes synchronously, and blocks other builds from progressing while it runs.

           The program executes with no arguments. The program's environment contains the following environment variables:

           DRV_PATH
               The derivation for the built paths.

               Example: /nix/store/5nihn1a7pa8b25l9zafqaqibznlvvp3f-bash-4.4-p23.drv

           OUT_PATHS
               Output paths of the built derivation, separated by a space character.

               Example: /nix/store/zf5lbh336mnzf1nlswdn11g4n2m8zh3g-bash-4.4-p23-dev /nix/store/rjxwxwv1fpn9wa2x5ssk5phzwlcv4mna-bash-4.4-p23-doc
               /nix/store/6bqvbzjkcp9695dq0dpl5y43nvy37pq1-bash-4.4-p23-info /nix/store/r7fng3kk3vlpdlh2idnrbn37vh4imlj2-bash-4.4-p23-man
               /nix/store/xfghy8ixrhz3kyy6p724iv3cxji088dx-bash-4.4-p23.

Seems like cachix push mycache $OUT_PATHS should do.

[domenkozar]

See cachix/cachix-action#19 for example usage

[domenkozar]

It is documented at https://docs.cachix.org/continuous-integration-setup/hydra.html, although it deserves it's own section.