butane/docs: add file append and overwrite examples

[JasonColapietro]

Summary

Moved over from coreos/butane#729
at @yasminvalim's suggestion, now that Butane development lives here.

butane/docs/examples.md showed contents but never append or overwrite,
so the difference between the three had to be inferred from the spec. This adds
three examples:

• appending a sudoers rule to the shipped /etc/sudoers, with the safe default
  overwrite: false
• the equivalent /etc/sudoers.d/ drop-in, which is usually preferable since it
  survives updates to the shipped file
• replacing a filesystem node with overwrite: true and ordinary contents

The sudoers examples deliberately allow a single command with exact arguments,
with a note against granting unrestricted passwordless access to shells, package
managers, or container runtimes.

Testing

• each of the three new blocks passes butane --check --strict, using a
  butane binary built from this tree
• ./test — Success, exit 0

The Go docs validator added in merged PR #2303 now covers the Butane examples.
The rebased tree passes both the Ignition docs check and the Butane docs check
with its local-file fixtures; butane/docs/examples.md contains 30 validated
sections, including these three examples. PR #2326 separately removes the
remaining duplicate shell validation loop.

Fixes #2270.

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---

📝 Walkthrough

Walkthrough

The documentation adds examples for appending sudoers rules and overwriting an existing filesystem node. The release notes record the file behavior documentation update.

Changes

File behavior documentation

Layer / File(s)	Summary
Document append and overwrite behavior butane/docs/examples.md, docs/release-notes.md	The examples show append with overwrite: false for sudoers files and overwrite: true for replacing /etc/example.conf. The release notes record these examples.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Other · Severity of issue fixed: Low

Suggested reviewers: prestist

Merge Risk: ⚪ Minimal · up to 9d745

The update documents file append and overwrite behavior without an identified functional or operational regression.

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes satisfy issue #2270. butane/docs/examples.md explains append and shows a sudoers rule appended to /etc/sudoers with overwrite: false. It also explains overwrite: true with `conte…
Out of Scope Changes check	✅ Passed	The changes stay within issue #2270. The added drop-in and filesystem-node replacement examples clarify the same file handling behavior. The release-note entry documents the completed issue work. No u…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Commit Message Convention	✅ Passed	The PR contains one non-merge commit. Its subject is butane/docs: add file append and overwrite examples. butane/docs is a valid subsystem prefix, add starts the description in lowercase imperat…
Title check	✅ Passed	The title follows the required format. It uses the subsystem prefix "butane/docs", an imperative lowercase description, and no trailing period. It accurately describes the documentation changes.
Description check	✅ Passed	The description clearly explains the three file-handling examples, their security guidance, migration context, issue reference, and reported test results. It is directly related to the changeset.

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Actionable comments posted: 1

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Inline comments:
In `@butane/docs/examples.md`:
- Line 152: Update the documentation example to clarify that contents with
overwrite: false does not replace a pre-existing filesystem node; instruct
readers to set overwrite: true when contents must replace the existing node,
while preserving the distinction between complete-file contents and append
behavior.

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docs/**

⚙️ CodeRabbit configuration file

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Files:

• docs/release-notes.md

🔇 Additional comments (3)

butane/docs/examples.md (2)

154-181: LGTM!

---

183-197: LGTM!

docs/release-notes.md (1)

19-19: LGTM!

[github-actions]

Binary size report (bin/amd64/ignition)

	Size
Base (main)	33MiB
PR (#2302)	33MiB
Delta	+0B (0.00%)

[prestist]

@JasonColapietro Thank you for working on this !!! Sorry about the delay, things have been a little chaotic. From my perspective this can land and lgtm. Regarding your question, if you are willing to add that feature back into this repo I would love any contributions! Definitely think it should go into a new pr tho.

[prestist]

The tmt, test will pass if you rebase with upstream. We had a spot where they were failing and that has since been fixed.

[JasonColapietro]

Thanks, Steven — rebased onto current upstream. The refreshed workflows are now waiting for maintainer approval to run, including TMT.

…

-Jason

[yasminvalim]

Thanks for working on this! LGTM!
I approved the workflow :)

[JasonColapietro]

Thanks, Yasmin — I appreciate the approval and the workflow run. Everything is green now.

Steven, the separate follow-up we discussed is #2303. It moves the Butane example checks into the existing Go docs validator so they also run without GNU coreutils, and it rejects incomplete markers and fences. Whenever you have time, I’d appreciate your take there.

[prestist]

@JasonColapietro I just approved 2303 and merged it, it looks like we still have a conflict that needs this PR rebased if you would not mind doing that? I can otherwise. Thank you again for all your efforts here.

[JasonColapietro]

@prestist Rebased — no need for you to do it. The only conflict was the release-note bullet, so both entries now sit under Changes, #2303's first and this one second. Force-pushed with --force-with-lease; the approvals survived and the checks started on their own this time, no workflow approval needed.

Verified on the rebased tree with the validator that landed in #2303:

• go run internal/util/tools/docs/docs.go — clean
• go run internal/util/tools/docs/docs.go -root butane/docs -files-dir "$tmp" — clean, and the three new blocks are among the 30 sections it now reports for butane/docs/examples.md

One thing I noticed while rebasing: test still has the original csplit + bin/butane loop over butane/docs/*.md after the new Go check, so those configs get validated twice, and that block makes ./test exit 1 when bin/butane hasn't been built. Deleting it was outside the scope of #2303, but I'm glad to send a small follow-up that drops it if you'd like — separate PR, same as before.

[JasonColapietro]

Opened the follow-up as #2326 — it drops the shell loop and leaves the Go check as the only pass over butane/docs, with the section counts in the body to show nothing stops being validated.

[JasonColapietro]

Thanks for the reviews! Rebased onto main now that #2303 has merged. The only conflict was the shared 2.28.0 release-note entry, resolved by keeping both bullets. The three new examples are also covered by the Butane docs validation that #2303 added, and they pass.