63 lines
1.6 KiB
Markdown
63 lines
1.6 KiB
Markdown
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# Flake Apps
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This note covers `39-flake-apps/`, which exposes runnable `apps.<system>` outputs instead of relying only on packages.
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---
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## 1. What an App Output Is
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An app output is a small attrset with a type and a program path:
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```nix
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apps.${system}.default = {
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type = "app";
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program = "${reportPackage}/bin/show-rollout-report";
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};
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```
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`nix run` looks for this schema. The program must already exist in the Nix store, so apps usually point at a package output.
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---
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## 2. Why This Example Still Defines Packages
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The runnable programs are built with `writeShellApplication`, then exposed in two ways:
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- `packages.<system>.report` and `packages.<system>.promote` build the scripts, and
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- `apps.<system>.default` and `apps.<system>.promote` tell `nix run` which program to execute.
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That separation keeps the build logic in packages and the command-line entry points in apps.
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---
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## 3. What the Example Demonstrates
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This example keeps the data a little richer than a one-line hello script:
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- one release train,
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- three rollout waves, and
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- one named app for the next promotion step.
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That makes it clear that app outputs are just pointers to real programs. They do not replace packages or change how the program is built.
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---
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## 4. What the Check Verifies
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`nix flake check` does not run apps automatically, so the example adds a check that executes both app program paths and verifies their output.
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That is the pattern to remember: expose the app through `apps`, then add an explicit check if you want CI to prove the command works.
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---
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## 5. Commands to Try
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```bash
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cd 39-flake-apps
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nix flake show
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nix run
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nix run .#promote
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nix flake check
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```
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