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If rubyfmt changes many lines, first confirm which formatter is running, then reproduce the result on a clean or otherwise reversible copy and inspect the diff before accepting it. A broad diff can reflect a first, consistent layout pass—not necessarily a code change or a formatter defect. The exact cause depends on your installed tool, invocation, and editor setup.
Why did rubyfmt change so many lines?
A formatter rewrites source layout. If a file or repository has not been formatted consistently before, one run can alter many lines at once. The available description of the fables-tales/rubyfmt project says it has no style-related configuration, so there may be no Rubyfmt setting to tune to preserve a preferred layout. That does not establish why any particular diff is large; the command, version, and editor path matter.
Start by distinguishing layout changes from changes to code. A large diff alone does not prove either that behavior changed or that it did not: review the edits and run the checks appropriate to the project.
1. Confirm the formatter and how it is invoked
Make sure the executable is the intended fables-tales/rubyfmt implementation. Ruby has other formatters with similar names, including rfmt and Rufo; their commands and options are not interchangeable. A Ruby LSP issue identifies fables-tales/rubyfmt and illustrates why the formatter selected by an editor or language-server integration should be checked: Ruby LSP issue #20.
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- Check the executable name and installed package, plus any project script that launches formatting.
- Check the editor’s formatter selection, extensions, and language-server configuration.
- Record the exact command and version used. Verify version-specific options in the documentation for the installed Rubyfmt version; its current release, maintenance status, CLI flags, and supported Ruby versions are not established here.
2. Reproduce the change safely
- Save or stash unrelated work so it cannot be mistaken for formatter output.
- Use a clean worktree or copy, or choose one representative Ruby file as a small test.
- Run the same formatter command used by your project or editor and capture the exact invocation.
- Compare the original file with the result in your version-control diff. Keep the test reversible until you understand the changes.
This isolates formatter output from concurrent edits and gives you a concrete diff to review. Formatting a sample first does not guarantee that a full repository run will produce only small changes.
3. Review the diff before accepting it
Read the changed lines rather than judging the diff by its size. Identify edits that appear to be layout-only, and investigate any changes that could alter code. Do not assume semantic equivalence without checking the relevant code and running the project’s tests or other appropriate checks. The available sources do not establish a universal semantic-preservation guarantee for every Rubyfmt version.
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If a broad mechanical reformat is expected and your project permits it, put it in a separate commit from functional work. That keeps later reviews easier to understand; it does not make the formatter’s output correct by itself.
4. Compare editor formatting with a deliberate run
If the noisy diff appears after saving a file, compare that result with a deliberate command-line run using the project’s intended formatter. If the outputs differ, investigate the editor’s formatter choice, extension defaults, and language-server settings. If they match, the editor may simply be invoking the same formatting behavior on save.
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The Ruby LSP discussion shows that formatter integration is a relevant concern, but it does not provide current setup instructions. Use the documentation for your actual editor, language server, and installed formatter rather than assuming an old issue describes today’s configuration.
5. Check project conventions and version consistency
Once you have identified the tool, check whether contributors and CI use the same formatter and version, following the project’s current documentation. A mismatch can make formatting results difficult to reproduce. Do not pin or upgrade to a particular version based on an unverified recommendation; first confirm the project’s supported version and the formatter’s current guidance.
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6. If Rubyfmt’s formatting approach does not fit
Do not look for Rubyfmt style settings unless the documentation for your exact version says they exist. The available Rubyfmt talk describes the project as having no style-related configuration. If your team needs configurable formatting, evaluate another formatter deliberately, checking its Ruby syntax support, editor and CI integration, configuration, check or diff modes, and the size of the changes it proposes.
Rufo is a separate formatter whose documentation describes a configuration file and a check mode: Rufo documentation. Those features do not mean Rubyfmt accepts Rufo configuration or flags. Switching tools can create a repository-wide style change, so review that migration separately rather than mixing it with unrelated code changes.
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