Equivalent of --max-jobs 0?

[Joachim Breitner]

I noticed that with lorri I am always a bit worried that I do something wrong, or my network goes down, and suddenly lorri will heat my my laptop to build rustc or something like that, instead of fetching it from a cache.

So I am wondering: Is there a supported and reliable way to get lorri into a state where it will never let nix build stuff locally: Either fetch everything needed for the shell from a cache, or fail the build.

Is this somehting that crossed your mind? How would I do that?

[Profpatsch]

So I am wondering: Is there a supported and reliable way to get lorri into a state where it will never let nix build stuff locally: Either fetch everything needed for the shell from a cache, or fail the build.

This sounds like a good candidate for a specific feature-flag in lorri.

It would pass --builders '' and --max-jobs 0 to the nix build, but we should kind of make sure the error messages that lorri gives are nice.

As far as implementation goes, I’d translate the flag to

lorri/src/nix/options.rs

Lines 1 to 19 in 0b3d330

 /// These options correspond to the nix options in `man nix.conf` 
 /// with the same names, though we only support a subset. 
 /// 
 /// You can use `.append(other)` to merge another `NixOptions`. 
 #[derive(Clone)] 
 pub struct NixOptions { 
     /// List of nix `builder` specifications 
     /// 
     /// * `None` use the ones configured in the nix config 
     /// * `Some([])`: use no builders 
     /// * `Some(list)`: use exactly `list` 
     pub builders: Option<Vec<String>>, 
     /// `substituter` hostnames 
     /// 
     /// * `None`: use the ones configured in the nix config 
     /// * `Some([])`: use no substituters 
     /// *`Some(list)`: use exactly `list` 
     pub substituters: Option<Vec<String>>, 
 } 

(needs a new struct field for max-jobs).

Maybe even add a provenance thingy to the nix options merge, so that if user sets conflicting flags there is a way to error out (or if there’s redundant flags there is a way to notify). Though I would say that is optional/orthogonal.