ob commands don't cache

[vaibhavsagar]

Running e.g. ob shell results in a rebuild each time when I would expect it to be cached after the first time, e.g.

vaibhavsagar@nixos-l14g3:~/repos/uptrust$ ob shell
./.obelisk/impl: command not cached, building ...
✔ Built on ./.obelisk/impl [command]
Hint: use '--no-interpret path/to/dependency' to force building an unpacked dependency and include it in this shell.

[nix-shell:~/repos/uptrust]$ exit
vaibhavsagar@nixos-l14g3:~/repos/uptrust$ ob shell
./.obelisk/impl: command not cached, building ...
✔ Built on ./.obelisk/impl [command]
Hint: use '--no-interpret path/to/dependency' to force building an unpacked dependency and include it in this shell.

How do I figure out why this is failing to cache?

[ryantrinkle]

@madeline-os Do you know anything about this?

[tdimiduk]

@ryantrinkle @madeline-os This was bugging me so I did some digging. It looks like the issue is the old version of nix thunk where caching is broken.

I've got a branch that gets caching working by updating nix-thunk to v0.7.0.1

https://github.com/tdimiduk/obelisk/tree/td/fix-nix-cache

However ReadThunkError lost it's show instance in this commit
obsidiansystems/nix-thunk@06f3a5e

So I had to comment out one bit of code to get it to compile.

I'd be happy to work on a PR to get caching working again, but there's some thornyness I'd need advice from Obsidian folks on how you'd like navigated. Obelisk would need larger changes to compile with all the way recent versions nix-thunk.

I see two main categories of solutions

Quick Hack (I could do this myself pretty easily)

• Update obelisk to nix-thunk v0.7.0.1
• do something about this line
  (https://github.com/obsidiansystems/obelisk/blob/master/lib/command/src/Obelisk/Command/Deploy.hs#L181
  Either rework that error message to not try to print the error or implement a printer for the error from within obelisk

Proper Solution (I'd probably need some help)

• Add the show instance (or some pretty printer) to nix-thunk for ReadThunkError
• Do the work to get obelisk working with nix-thunk latest. There are some larger API changes in nix-thunk that obelisk would need to catch up with.

[alexfmpe]

@tdimiduk see d799ab9 which bumps nix-thunk to 0.7.1 but the PR containing it (#1093) is blocked on the nix CI being down

[alexfmpe]

Ah actually, the migration to nix-thunk 0.7.0.1 happened earlier in the same PR. Here's the fix to the missing Read instance: 961f157#diff-0eb97b72c7ccff8bca8f6a20f18a4d718cc43abb335c9cf1512b82f0ed52a75dL181

[tdimiduk]

Thanks for the context. Anything an interested outsider can do to help Obelisk PRs with merging faster? I see a lot of good work sitting in review that it seem like must be a bit of a hassle to keep track of.