How do I use mkCargoDerivation to replace buildDepsOnly

[dpc]

-        workspaceDeps = craneLib.buildDepsOnly (commonArgs // {
+        workspaceDeps = craneLib.mkCargoDerivation (commonArgs // {
+          pnameSuffix = "-deps";
+          version = "0.0.1";
+          cargoArtifacts = null;
+          src = (craneLib.mkDummySrc { src = ./.; });
           buildPhaseCargoCommand = "cargo doc --profile $CARGO_PROFILE ; cargo check --profile $CARGO_PROFILE --all-targets ; cargo build --profile $CARGO_PROFILE --all-targets";
           doCheck = false;
+          doInstallCargoArtifacts = true;
         });

I tried this one and it fails miserably with:

> nix build -L .#workspaceBuild                                                                                             
warning: Using saved setting for 'extra-substituters = https://fedimint.cachix.org' from ~/.local/share/nix/trusted-settings.json.                                                                                                                      
warning: ignoring untrusted flake configuration setting 'extra-substituters'                                                
warning: Using saved setting for 'extra-trusted-public-keys = fedimint.cachix.org-1:FpJJjy1iPVlvyv4OMiN5y9+/arFLPcnZhZVVCHCDYTs=' from ~/.local/share/nix/trusted-settings.json.                                                                        
warning: ignoring untrusted flake configuration setting 'extra-trusted-public-keys'                                         
error: the string '# This file is automatically @generated by Cargo.                                                                                                                                                                                    
       # It is not intended for manual editing.                                                                             
       version = 3                                                                                                          
                                                                                                                            
       [[package]]       

REST OF MY Cargo.lock

       ' is not allowed to refer to a store path (such as '')

       at /nix/store/a3621jkl02cnlb9943jikqhhgqz7xscs-source/lib/vendorCargoDeps.nix:46:10:

           45|
           46|   lock = builtins.fromTOML cargoLockContents;
             |          ^
           47|   lockPackages = lock.package or (throw "Cargo.lock missing [[package]] definitions");
(use '--show-trace' to show detailed location information)

BTW. I'm 95% that I filled an issue already asking this as a question and can't find anywhere anymore.

[dpc]

I've found https://discourse.nixos.org/t/not-allowed-to-refer-to-a-store-path-error/5226 describing the issue, and from what I understand nix doesn't like the fact that the content of toml file from a store is used somewhere. But I don't understand how would I avoid it, and even more so - how does the normal lib.buildOnlyDeps works, doing effectively the same thing?

[ipetkov]

Here's where the issue is:

• if mkCargoDerivation is not supplied with an input for cargoVendorDir it will call vendorCargoDeps args
• if vendorCargoDeps is not supplied with an input for cargoLockContents it will try to look for a cargoLock path
• if vendorCargoDeps is not supplied with an input for cargoLock it will try to check for a Cargo.lock file under src

Kind of weird that builtins.fromTOML doesn't like store paths... Normally when you pass in src = ./whatever; the input turns into ./whatever/Cargo.lock which is a path the builtin can access. But setting src = mkDummySrc ...; turns it into a store path and hence boom.

There are a couple of ways around it:

• set cargoVendorDir = vendorCargoDeps { src = ./.; }; explicitly
• set cargoLock = ./src/Cargo.lock; explicitly
• set cargoLockContents = ...; to the actual contents of the Cargo.lock file

But I don't understand how would I avoid it, and even more so - how does the normal lib.buildOnlyDeps works, doing effectively the same thing?

buildDepsOnly takes the first approach above, effectively passing in the original src to vendorCargoDeps but passing the dummified source to mkCargoDerivation

[dpc]

Thanks! I confirm that this fixes it! But it doesn't make a great UI. :D

[ipetkov]

I agree this is a bit annoying, not an edge case I was able to anticipate 😅

Maybe there is some unsafeDiscardStringContext that might help but I'm not fully sure

[dpc]

Maybe a different api would do. It seems that calling mkDummySrc is inconvenient, but as a I user, I don't care about being able to call mkDummySrc directly anyway. Sure, being able to call it seems most flexible, but it also exposes the user to all the internal problems.

Just thinking aloud.