Nixpkgs: channels do not advance? (e.g. nixos-unstable-small)

[xaverdh]

Describe the bug
On hydra unstable-small appears to build fine, but the channel does not advance ?

[doronbehar]

Same with unstable, something is blocking it...

[xaverdh]

Only nixpkgs-* channels appear to make progress, although the tested jobs for the other channels do succeed. I also updated my system directly against a nixpkgs commit from one of the succeeding builds, it works just fine (everything was in cache, as expected).

[xaverdh]

So something in the channel update mechanism is broken I guess? Who do you ping for this?

[xaverdh]

Ok, judging from the channel-script repo:
cc @grahamc

[xaverdh]

The unstable-small channel just updated, unstable is still stuck.

[peterhoeg]

A workaround for people using a local checkout of nixpkgs is to use the commit id for the most recent completed evaluation instead of the channel name. For unstable as of right now that 683c68232e9.

[vcunat]

They don't even need a local checkout, e.g.:

nixos-rebuild -I nixpkgs=https://github.com/nixos/nixpkgs/archive/683c682.tar.gz ...

[i077]

nixos-unstable advanced to 683c682 3 hours ago.