57 lines
1.4 KiB
Markdown
57 lines
1.4 KiB
Markdown
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# Lib Outputs
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This note covers `42-lib-outputs/`, which exposes a `lib` attrset with pure data and helper functions that other outputs can reuse.
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---
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## 1. Why `lib` Is Useful
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Only some output names have special meaning to the `nix` CLI. A flake can still expose arbitrary attrs for consumers.
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`lib` is a common convention for that. It is a good place for:
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- pure helper functions,
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- derived lookup tables, and
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- reusable domain data.
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This example keeps the `lib` attrset small so the distinction is clear: the flake exports logic, not just build targets.
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---
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## 2. What the Example Exports
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The `lib` output contains:
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- `rolloutPlan`, a small list of pure data,
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- `ownerByService`, derived from that list, and
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- `renderStep` plus `renderPlan`, which turn the data into text.
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The package output then prints `self.lib.renderPlan`, so the runnable artifact is built from the same exported helper values that outside consumers can evaluate.
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---
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## 3. Why the Check Uses `self.lib`
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The check reaches back through the public output path:
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```nix
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apiOwner = self.lib.ownerByService.api;
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workerLine = self.lib.renderStep (builtins.elemAt self.lib.rolloutPlan 1);
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```
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That matters because it proves the helper data is not only local implementation detail in a `let` block. It is part of the flake interface.
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---
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## 4. Commands to Try
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```bash
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cd 42-lib-outputs
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nix flake show
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nix eval .#lib.ownerByService.api --raw
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nix build
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./result/bin/show-lib-plan
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nix flake check
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```
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