58 lines
1.4 KiB
Markdown
58 lines
1.4 KiB
Markdown
# Follows and Inputs
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This note covers `15-follows-and-inputs/`, which defines multiple inputs and uses `follows` so one transitive input is reused instead of resolved separately.
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---
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## 1. What `follows` Does
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`follows` points one input at another input by name:
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```nix
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flake-utils = {
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url = "github:numtide/flake-utils";
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inputs.systems.follows = "systems";
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};
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```
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That means `flake-utils` does not resolve its own separate `systems` input. It reuses the top-level `systems` input from this flake.
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---
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## 2. Why This Matters
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Without `follows`, transitive dependencies can drift apart. Two flakes may each resolve their own copy of an input, even though you wanted them to share one.
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This example keeps the case small:
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- one top-level `systems` input,
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- one dependent flake, `flake-utils`, and
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- one `follows` edge that ties them together.
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That makes it easy to inspect with `nix flake metadata`.
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---
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## 3. Why the Example Still Builds Something
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The flake uses `flake-utils.lib.eachDefaultSystem` so the dependency is not just declared, but actually used. The package itself stays trivial because the point of the example is the input graph, not the package.
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If you want to compare output-generation styles, see `03-multi-system/`. This example is about input wiring.
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---
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## 4. Commands to Try
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```bash
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cd 15-follows-and-inputs
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nix flake metadata
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nix flake show
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nix build
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./result/bin/show-follows
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nix run
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nix flake check
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```
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