Local Path Inputs

This note covers 40-path-inputs/, which uses inputs.catalog.url = "path:./catalog"; to pull another local flake into the parent flake.

1. What a Local Path Input Looks Like

A local input is declared with a path: flake reference:

inputs.catalog.url = "path:./catalog";

The target directory must itself be a flake, so catalog/ contains its own flake.nix.

2. What the Child Flake Exposes

The child flake in this example does not build packages. It exports pure data through lib:

one release name,
one service-owner map, and
one rollout plan.

The parent flake reads those values and turns them into a runnable script.

3. Why This Example Uses `lib`

Using lib keeps the focus on the input boundary, not on packaging details in both flakes.

That is the important part of path: inputs: once the child is a flake, its outputs are consumed the same way as any other flake input.

4. The Git-Tracked File Rule Still Applies

This is still a flake input, so Nix reads it from the flake source tree. Files inside catalog/ must be tracked, or the parent flake will not see them during pure evaluation.

That rule is easy to miss when the child flake lives in the same repository.

5. Commands to Try

cd 40-path-inputs

nix flake metadata
nix build
./result/bin/show-local-plan
nix flake check

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