feat(nix): install completions

[betaboon]

Summary by CodeRabbit

• New Features

  • Shell completion for Bash, Fish, and Zsh is now available and will be automatically installed on supported platforms.

• Chores

  • Telemetry is disabled by default during installation to prevent automatic data reporting.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Run ID: da17a8ef-b462-4987-8627-cbc281dbea82

📥 Commits

Reviewing files that changed from the base of the PR and between 4cad923 and 253838a.

📒 Files selected for processing (1)

• flake.nix

🚧 Files skipped from review as they are similar to previous changes (1)

• flake.nix

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📝 Walkthrough

Walkthrough

The flake.nix adds installShellFiles to nativeBuildInputs and a conditional postInstall hook that, when the build can run the host platform, exports OPENSPEC_TELEMETRY=0 and generates/installs Bash, Fish, and Zsh completions for the openspec CLI.

Changes

Cohort / File(s)	Summary
Build Configuration flake.nix	Added installShellFiles to nativeBuildInputs and introduced a conditional postInstall hook that exports OPENSPEC_TELEMETRY=0 and generates/installs shell completions for openspec (Bash, Fish, Zsh). No other phases or public interfaces changed.

Sequence Diagram(s)

sequenceDiagram
    participant Builder as Builder (nix build)
    participant Host as Host Platform
    participant Openspec as `${out}/bin/openspec`
    participant Shells as Shell completion dirs

    Builder->>Host: Check canRun (buildPlatform == hostPlatform)
    alt can run on host
        Builder->>Host: export OPENSPEC_TELEMETRY=0
        Host->>Openspec: run "openspec --completion bash/fish/zsh"
        Openspec-->>Shells: write completion files to $out/.../share/{bash,fish,zsh}/completions
        Builder->>Shells: install completion files
    else cannot run
        Builder-->>Builder: skip postInstall completion generation
    end

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested reviewers

• TabishB

Poem

🐰 I hopped through nix to plant a seed,
Completions sprout for those in need,
Bash, Fish, Zsh — all snugly dressed,
Telemetry quiet, installs at rest,
A tiny hop, the CLI's at speed.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding shell completion installation to the Nix flake build process, which is the core objective of the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[betaboon]

@TabishB is there anything missing here? :)

[TabishB]

@betaboon we've made completion installation opt-in recently. would be good to make it standard across the board.

Mainly because of this issue: #948
ref PR: #949

[betaboon]

it's rather unusual in nixpkgs to make the installation of completions optional.
The upstream package-definition for OpenSpec also just installs the completions.

The problem described in #948 is pretty much ruled out in nix/nixos.

some additional detail:
the postinstall is not used here, just the openspec completion generate command and the output is written to $out/share/bash-completions etc.