nixos: implement hints for failing units on activation

[NotAShelf]

Initial support for better handling of activation errors in the NixOS module. The implementation is complete, but is not available in Home Manager and Darwin platforms due to lack of maintainer time.

Implements systemctl hints feature akin to nixos-rebuild that displays a hint for failing systemctl services if the user opts in.

Summary by CodeRabbit

• New Features

  • Added --show-systemctl-hints / NH_SHOW_SYSTEMCTL_HINTS and an explicit rebuild-and-activate flow for Switch/Boot/Test; VM/Build remain build-only.
  • New xtask dist/completions tooling to generate manpages and shell completions.

• Removed

  • Removed built-in completions command from the main CLI; completion generation moved to xtask.

• Bug Fixes

  • Improved, actionable activation error messages with systemctl/journalctl hints.

• Documentation

  • Major README rewrite and changelog cleanup.

• Refactor

  • Split OS operations into build-only vs. rebuild-and-activate workflows; packaging/install flow consolidated.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

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📥 Commits

Reviewing files that changed from the base of the PR and between 9f1dedd and aa80793.

📒 Files selected for processing (2)

• package.nix (3 hunks)
• src/nixos.rs (6 hunks)

Walkthrough

Reworks NixOS rebuild/activation into distinct build-only and rebuild-and-activate flows via a new public OsRebuildActivateArgs (wraps OsRebuildArgs and adds show_systemctl_hints), updates Switch/Boot/Test to use it, removes the in-tree completions command/module, and moves completion/man generation into xtask.

Changes

Cohort / File(s)	Summary
CLI surface / types src/interface.rs	Added public OsRebuildActivateArgs (flattens OsRebuildArgs, adds show_systemctl_hints: bool with clap env/flag). Updated OsSubcommand variants Switch, Boot, Test to use OsRebuildActivateArgs; Build remains OsRebuildArgs. Removed Completions variant and the public CompletionArgs/Shell types. Adjusted feature-requirement branching to inspect nested rebuild for Test.
NixOS rebuild & activation logic src/nixos.rs	Introduced two-phase paths: build_only (used by Build/BuildVm) and rebuild_and_activate (used by Switch/Boot/Test). Added activate_rebuilt_config to handle optional confirmation, copying, activation (switch/test), bootloader steps, elevation/SSH handling, and conditional systemctl troubleshooting hints controlled by show_systemctl_hints. Refactored call sites to use self.rebuild for build helpers.
Completion removal (runtime) src/completion.rs, src/lib.rs, src/main.rs	Deleted the completion submodule and its run() implementation; removed the completion module export and module import from crate root and main. CLI no longer exposes an internal completions command.
xtask: completion & man generation tooling xtask/src/comp.rs, xtask/src/man.rs, xtask/src/main.rs, xtask/Cargo.toml	Added xtask completion generator (comp.rs) with CompletionShell and generate(...); refactored man generator to return Result and improved error handling; extended xtask CLI to accept Completions (out_dir, optional shell), changed Man out_dir default, added Dist to run man + completions in parallel; updated xtask dependencies.
Docs / README README.md	Large rewrite and reorganization: broadened scope beyond NixOS, reorganized features/design/usage, added NH_SHOW_SYSTEMCTL_HINTS env var doc and other editorial/content updates.
Changelog CHANGELOG.md	Removed in-tree completions note and updated Unreleased entries; added note that completion generation moved to xtask.
Cargo manifest Cargo.toml	Removed clap_complete and clap_complete_nushell from main crate deps; bumped hotpath version; transient clippy edits.
Nix packaging package.nix	Added stdenv param, switched TOML import to lib.importTOML, simplified postInstall to call cargo xtask dist, removed manual completion generation loop, adjusted lockfile handling.
Ignored files .gitignore	Added /comp and /man to ignores; removed prior gen* exception.

Sequence Diagram(s)

sequenceDiagram
    participant CLI as CLI (OsArgs)
    participant ActivateArgs as OsRebuildActivateArgs
    participant Builder as Builder (build_only / rebuild)
    participant Activator as activate_rebuilt_config
    participant System as System (profiles / systemctl / bootloader)

    CLI->>ActivateArgs: parse args (Switch/Boot/Test -> ActivateArgs)
    alt Build-only (Build / BuildVm)
        ActivateArgs->>Builder: build_only(...)
        Builder-->>CLI: built artifacts + post-build instructions
    else Activate path (Switch/Boot/Test)
        ActivateArgs->>Builder: rebuild_and_activate (build phase)
        Builder-->>ActivateArgs: artifacts (out_path, final_attr)
        ActivateArgs->>Activator: activate_rebuilt_config(subcmd, final_attr, show_systemctl_hints)
        Activator->>System: perform activation / bootloader steps
        System-->>Activator: result (success / unit failures)
        alt failure & show_systemctl_hints
            Activator-->>CLI: failure + systemctl troubleshooting hints
        else
            Activator-->>CLI: success or standard error
        end
    end

Loading

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

• Heterogeneous changes across public CLI types, core NixOS control flow, removal of a runtime subcommand, and migration of completion tooling to xtask.
• Files requiring extra attention:
  • src/interface.rs — public API/clap attributes and feature-requirement logic.
  • src/nixos.rs — correctness of split build vs activate flows, elevation/SSH handling, activation error wrapping, and bootloader steps.
  • xtask/* — completion/man generation APIs and Dist orchestration.
  • Ensure no dangling imports or references to removed completion types in src/*.

Possibly related PRs

• nh: add nushell completions #477 — Touches completion implementation; likely to conflict with removal of in-tree completion command and types because that PR added Nushell support to completion generation.

Suggested reviewers

• faukah

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 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 primary change: implementing hints for failing units on activation in the nixos module, which aligns with the scope and objectives of the PR.

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Actionable comments posted: 1

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Review profile: CHILL

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Reviewing files that changed from the base of the PR and between c81b763 and 2b665ee.

📒 Files selected for processing (2)

• src/interface.rs (1 hunks)
• src/nixos.rs (1 hunks)

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🔇 Additional comments (2)

src/interface.rs (1)

240-243: LGTM! Clean flag implementation.

The flag is properly configured with both CLI and environment variable support, and defaults to opt-in behavior (false).

src/nixos.rs (1)

373-373: LGTM! Good addition for debugging visibility.

Showing output during activation helps users understand what's happening and is consistent with other command executions in this file.

[coderabbitai]

Actionable comments posted: 2

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

src/nixos.rs (1)

160-168: Fix nix build --profile SYSTEM_PROFILE to pass the system closure, not the binary path

The code at line 263 passes canonical_out_path (the switch-to-configuration binary) to nix build --profile, but --profile expects a system closure directory, not a binary file. Profiles are versioned directories (normally symlinks) that should point to configuration roots in the store, not individual binaries.

Currently:

• Line 221-224: canonical_out_path is set to the path of the switch-to-configuration binary
• Line 263: This binary path is passed to nix build --profile SYSTEM_PROFILE

This causes /nix/var/nix/profiles/system to point to the binary rather than the system closure, breaking generation handling and differing from standard nixos-rebuild behavior.

Fix: Pass target_profile (the system closure) to nix build --profile, not canonical_out_path:

    let canonical_profile = target_profile
      .canonicalize()
      .context("Failed to resolve output path")?;

    let switch_to_configuration = canonical_profile
      .join("bin")
      .join("switch-to-configuration")
      .canonicalize()
      .context("Failed to resolve switch-to-configuration path")?;

    // ... later, in the Boot | Switch branch:
    Command::new("nix")
      .elevate(...)
      .args(["build", "--no-link", "--profile", SYSTEM_PROFILE])
-     .arg(canonical_out_path)
+     .arg(canonical_profile.to_str().ok_or_else(|| {
+       eyre!("canonical_profile path contains invalid UTF-8")
+     })?)
      .ssh(...)

Also update line 227 to use &switch_to_configuration directly instead of canonical_out_path for the Test/Switch activation command.

♻️ Duplicate comments (1)

src/nixos.rs (1)

181-188: Activation error handling and systemctl hints are much more robust now

The new map_err block uses format!("{e:#}") to preserve the full error chain and lowercases it before checking for service/unit failure patterns (e.g. “units failed”, “failed” + “service”/“unit”). Gating the additional systemd troubleshooting hints on both this heuristic and self.show_systemctl_hints gives users an opt‑in hinting mode without losing detailed error context.

Aside from the profile path issue noted separately, this activation error wrapping is a solid improvement over the previous plain‑string match.

Also applies to: 221-254

🧹 Nitpick comments (3)

README.md (1)

33-40: Minor wording/tone cleanups are possible but non-blocking

There are a few small style nits LanguageTool flagged (e.g. “3rd party” → “third‑party”, “cool looking UIs” → “cool‑looking UIs”, “Platform specific” → “Platform‑specific”, “grown a lot over the years”, “talked about NH”). None of these block understanding, but tightening phrasing and adding hyphens where appropriate would polish the README further if you’re touching this text again.

Also applies to: 45-52, 55-58, 71-82, 233-237, 372-399

src/interface.rs (1)

248-256: Confirm clap env parsing semantics for NH_SHOW_SYSTEMCTL_HINTS

show_systemctl_hints: bool with #[arg(long, env = "NH_SHOW_SYSTEMCTL_HINTS")] will use clap’s default boolean parsing (accepting e.g. 1/0, true/false, etc.). The README and changelog only mention "1".

You might want to clarify accepted values in docs or explicitly use a BoolishValueParser if you want stricter semantics; otherwise the implementation is fine as‑is.

If you want to double‑check clap’s current bool/env behavior for your version, please consult the latest clap 4.x docs.

src/nixos.rs (1)

101-147: Rebuild/activate refactor is a nice separation, with a couple of small cleanups possible

The new split between:

• OsRebuildActivateArgs::rebuild_and_activate (Boot/Switch/Test),
• OsRebuildArgs::build_only (Build/BuildVm), and
• helper methods (setup_build_context, determine_output_path, resolve_installable_and_toplevel, resolve_specialisation_and_profile, handle_dix_diff)

is a big improvement in readability and reusability. The build phase is clearly separated from activation and VM handling.

A couple of minor nits:

• In rebuild_and_activate, the VM‑specific warning branch:

  if self.rebuild.hostname.is_none()
    && matches!(variant, OsRebuildVariant::BuildVm)
    && final_attr.is_some_and(|attr| attr == "vm" || attr == "vmWithBootLoader")
  {
      ...
  }

  is currently unreachable because rebuild_and_activate is only called with Boot, Switch, or Test (BuildVm uses OsRebuildArgs::build_only). This can be removed or moved alongside the BuildVm call site for clarity.

• The comment above OsRebuildArgs::build_only says “Used by Build subcommand which doesn't activate,” but it is also used by BuildVm. Updating the comment to reflect both callers would avoid confusion.

Otherwise the flow and flag handling (including --ask and --dry semantics for activation vs pure builds) look consistent.

Also applies to: 324-376, 444-476

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📒 Files selected for processing (5)

• CHANGELOG.md (2 hunks)
• Cargo.toml (1 hunks)
• README.md (7 hunks)
• src/interface.rs (3 hunks)
• src/nixos.rs (6 hunks)

✅ Files skipped from review due to trivial changes (1)

• Cargo.toml

🧰 Additional context used

🧬 Code graph analysis (1)

src/nixos.rs (1)

src/commands.rs (7)

• args (255-264)
• elevate (220-223)
• message (268-271)
• message (676-679)
• new (205-216)
• new (665-673)
• new (788-797)

🪛 LanguageTool

README.md

[grammar] ~39-~39: Use a hyphen to join words.
Context: ..._ tool that brings together relevant 3rd party projects that you might be familia...

(QB_NEW_EN_HYPHEN)

---

[grammar] ~54-~54: Use a hyphen to join words.
Context: ...se. I mean who does not love some cool looking UIs? - **Build-tree Visualizat...

(QB_NEW_EN_HYPHEN)

---

[style] ~72-~72: This phrasing can be wordy. For improved clarity, try opting for something more concise.
Context: ...port into a single, convenient utility. For the time being, this appears in NH's interface as supp...

(FOR_THE_TIME_BEING)

---

[grammar] ~74-~74: Use a hyphen to join words.
Context: ...provide a familiar, convenient and good looking interface for users of any and ...

(QB_NEW_EN_HYPHEN)

---

[style] ~75-~75: ‘any and all’ might be wordy. Consider a shorter alternative.
Context: ...d good looking interface for users of any and all of those projects. The familiar interf...

(EN_WORDINESS_PREMIUM_ANY_AND_ALL)

---

[grammar] ~233-~233: Use a hyphen to join words.
Context: ...width="750px" >

### Platform Specific Subcommands Platform specific ...

(QB_NEW_EN_HYPHEN)

---

[grammar] ~235-~235: Use a hyphen to join words.
Context: ... Platform Specific Subcommands Platform specific subcommands are those that impl...

(QB_NEW_EN_HYPHEN)

---

[style] ~372-~372: Consider a different phrase to strengthen your wording.
Context: ...as had a long history, and it has grown a lot over the years. I, NotAShelf, would fir...

(A_LOT_CONSIDERABLY)

---

[style] ~399-~399: This phrase can be considered informal. To elevate your writing, consider using a more professional alternative.
Context: ... to everyone who has contributed to NH, talked about NH or criticized NH to allow further im...

(TALK_ABOUT_DISCUSS)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (5)

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🔇 Additional comments (3)

CHANGELOG.md (1)

39-40: Changelog otherwise aligns with interface changes

The nushell support and the whitespace‑splitting fix both look consistent with the code changes (Shell::Nushell variant and argument splitting changes elsewhere). No further action needed here.

Also applies to: 50-51

src/interface.rs (2)

127-151: OsRebuildActivateArgs wrapper and feature detection look sound

Switch/Boot/Test now carry OsRebuildActivateArgs, and get_feature_requirements correctly defers to args.rebuild.uses_flakes(), so feature probing should remain equivalent to the old behavior. The wrapper’s #[command(flatten)] pub rebuild: OsRebuildArgs keeps the existing flags (incl. --install-bootloader, --hostname, etc.) available while adding --show-systemctl-hints / NH_SHOW_SYSTEMCTL_HINTS.

This API shape looks good and should be stable for future activation‑only flags.

Also applies to: 248-256

---

165-190: Nushell completion wiring appears correct; ensure generator side is updated

Adding Shell::Nushell with #[value(alias = "nu", name = "nushell")] matches the changelog entry and should let nh completions nushell/nu parse correctly. Assuming the completions generation code (where CompletionArgs.shell is matched) has a corresponding arm for Shell::Nushell, this change looks complete.

Just confirm the completions handler covers the new variant and that nushell output matches expectations.

Also applies to: 597-612

[coderabbitai]

Actionable comments posted: 1

♻️ Duplicate comments (2)

CHANGELOG.md (1)

39-47: Changelog entry overstates systemctl hints behavior.

This entry claims the flag "displays failing systemd units at the end of the rebuild log," but the actual implementation provides generic systemd troubleshooting hints rather than parsing and listing specific failed units.

README.md (1)

307-311: Environment variable documentation overstates current behavior.

The description claims NH will "parse activation logs and isolate specific unit failures to display them at the end," but the actual implementation provides generic systemd troubleshooting hints when activation fails, rather than parsing and listing specific failed units.

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• README.md (7 hunks)
• xtask/Cargo.toml (1 hunks)
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🧰 Additional context used

🧬 Code graph analysis (1)

xtask/src/main.rs (2)

xtask/src/comp.rs (1)

• generate (40-67)

xtask/src/man.rs (1)

• generate (6-101)

🪛 LanguageTool

README.md

[grammar] ~39-~39: Use a hyphen to join words.
Context: ..._ tool that brings together relevant 3rd party projects that you might be familia...

(QB_NEW_EN_HYPHEN)

---

[grammar] ~53-~53: Use a hyphen to join words.
Context: ...se. I mean who does not love some cool looking UIs? - **Build-tree Visualizat...

(QB_NEW_EN_HYPHEN)

---

[style] ~71-~71: This phrasing can be wordy. For improved clarity, try opting for something more concise.
Context: ...port into a single, convenient utility. For the time being, this appears in NH's interface as supp...

(FOR_THE_TIME_BEING)

---

[grammar] ~73-~73: Use a hyphen to join words.
Context: ...provide a familiar, convenient and good looking interface for users of any and ...

(QB_NEW_EN_HYPHEN)

---

[style] ~74-~74: ‘any and all’ might be wordy. Consider a shorter alternative.
Context: ...d good looking interface for users of any and all of those projects. The familiar interf...

(EN_WORDINESS_PREMIUM_ANY_AND_ALL)

---

[grammar] ~232-~232: Use a hyphen to join words.
Context: ...width="750px" >

### Platform Specific Subcommands Platform specific ...

(QB_NEW_EN_HYPHEN)

---

[grammar] ~234-~234: Use a hyphen to join words.
Context: ... Platform Specific Subcommands Platform specific subcommands are those that impl...

(QB_NEW_EN_HYPHEN)

---

[grammar] ~275-~275: Ensure spelling is correct
Context: ...will call the necessary script to force and installation of your bootloader. Th...

(QB_NEW_EN_ORTHOGRAPHY_ERROR_IDS_1)

---

[style] ~371-~371: Consider a different phrase to strengthen your wording.
Context: ...as had a long history, and it has grown a lot over the years. I, NotAShelf, would fir...

(A_LOT_CONSIDERABLY)

---

[style] ~398-~398: This phrase can be considered informal. To elevate your writing, consider using a more professional alternative.
Context: ... to everyone who has contributed to NH, talked about NH or criticized NH to allow further im...

(TALK_ABOUT_DISCUSS)

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🔇 Additional comments (5)

xtask/Cargo.toml (2)

8-13: Dependency additions support the new completion generation flow.

The additions of clap_complete, clap_complete_nushell, and the version bump of clap_mangen properly support the migration of completion generation to the xtask workflow.

---

8-13: xtask/Cargo.toml appears correctly formatted per project rules; verify via CI or local Taplo run.

The project's .taplo.toml specifies align_entries = true with column_width = 100. The current xtask/Cargo.toml formatting shows properly aligned entries in both [package] and [dependencies] sections, consistent with these rules. However, since the Taplo tool is unavailable in this environment, run taplo fmt --check xtask/Cargo.toml locally or confirm the formatting passes CI checks.

xtask/src/main.rs (3)

20-39: Command enum enhancements improve CLI usability.

The updated Command enum with explicit defaults for output directories and the new Dist variant for generating both manpages and completions together provides a cleaner, more intuitive interface.

---

41-47: Improved error handling in main function.

The change to return Result and the explicit error handling for directory changes with a clear error message is a significant improvement over previous panic-based error handling.

---

54-69: Parallel generation in Dist command is well-implemented.

The parallel execution of manpage and completion generation is properly implemented with:

• Thread panic handling
• Proper error propagation
• No resource conflicts (separate output directories)

[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

xtask/src/main.rs (1)

20-38: CLI wiring for Man/Completions/Dist looks good; consider de-duplicating default output dirs

The new subcommands and flags are consistent with man::generate/comp::generate, and shell: Option<CompletionShell> maps cleanly to “all shells if omitted”. One small improvement: Command::Dist hard-codes "man" and "comp" while the Man/Completions variants have their own default directories. If those defaults ever change, Dist will silently diverge.

Consider centralizing the default paths (e.g., shared constants or a helper) and using them both in the clap attributes and in the Dist branch to keep behavior in sync.

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xtask/src/main.rs (2)

xtask/src/comp.rs (1)

• generate (40-67)

xtask/src/man.rs (1)

• generate (6-101)

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🔇 Additional comments (3)

src/darwin.rs (2)

62-64: LGTM! Improved error message accuracy.

The updated error message correctly references "nh darwin" instead of "nh os", which provides clearer guidance to users running Darwin-specific commands.

---

77-77: LGTM! Platform-specific temp directory naming.

The temp directory prefix now correctly uses "nh-darwin" instead of "nh-os", which improves debugging clarity and aligns with the Darwin-specific context of this module.

xtask/src/main.rs (1)

41-66: The review comment is based on an incorrect premise and should be ignored

The core claim—that "String does not implement std::error::Error, so String → Box via .into() will not type-check"—is false. The Rust standard library implements From for Box by wrapping the String in a private StringError newtype, allowing String values to be converted into Box via .into().

The current code is valid and will compile without modification. The .map_err(|e| e.into()) conversions correctly transform String errors into Box<dyn Error> through the standard library's conversion implementation. No changes are required.

Likely an incorrect or invalid review comment.

[NotAShelf]

Okay, I'm done. 4AM is clearly not a good time to implement your things.

[minhtrancccp]

as nh completions is no longer supported, should i make an issue to track support for sourcing flake pkg's shell completions at startup?

[NotAShelf]

I'm a little confused to why you would need to do this on startup?

The current package should install them as the previous one did, but I guess this requires you to be using NixOS?

P.S. I'm back at the hospital today and won't have access to my main system for a few days. Feel free to create an issue about it.