Using workspaces with small closures

[jmgilman]

Background

I have a repository setup as such:

Cargo.toml
Cargo.lock
src/pkg1/Cargo.toml
src/pkg2/Cargo.toml
src/pkg3/Cargo.toml

The root Cargo.toml establishes a workspace as such:

[workspace]
members = [
  "src/pkg1",
  "src/pkg2",
  "src/pkg3"
]

Then packages are built as such:

# ...
naersk.buildPackage {
  inherit name version;

  root = inputs.self;

  cargoBuildOptions = x: x ++ ["--package" "${name}"];
  cargoTestOptions = x: x ++ ["--package" "${name}"] ;
}

Problem

The above derivation captures the entire repository (because of inputs.self). Thus, when anything in the repository changes, the input hash changes and causes a rebuild of any of the packages.

If I filter root to only include the source of a single package, cargo fails because it expects all packages defined in the workspace to exist on the filesystem. For example, if I filter only to include src/pkg1, it fails with:

opening file '/nix/store/abc123-source/pkg2/Cargo.toml': No such file or directory

This creates a problematic setup because I cannot disassociate the projects such that changes in one do not invalidate another one. I imagine I must be doing something wrong here. Is there a way to isolate workspace packages to avoid this problem?

[jmgilman]

For additional context, I tried using the targets option instead of specifying the --package flag and it built the entire workspace. I looked through the source and it looks like it's not wired up to anything, so I think the documentation might be outdated.

[Patryk27]

I see - maybe members = [ "src/*" ] (+ filtering-out unnecessary directories through Nix) will do it?

I looked through the source and it looks like it's not wired up to anything [...]

Whoopsie, yeah - looks like it 😅

[jmgilman]

Hmm, doesn't look like it works as one might expect. Cargo still tries to find the specific workspace members. I'm not sure you can override it like that, cargo still uses the root Cargo.toml to determine the workspace members.