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Add a note on line-too-long to the formatter docs
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charliermarsh committed Oct 28, 2023
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14 changes: 8 additions & 6 deletions docs/faq.md
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## Is the Ruff linter compatible with Black?

Yes. The Ruff linter is compatible with [Black](https://github.com/psf/black) out-of-the-box, as
long as the `line-length` setting is consistent between the two.
long as the [`line-length`](settings.md#line-length) setting is consistent between the two.

Ruff is designed to be used alongside a formatter (like Ruff's own formatter, or Black) and, as
such, will defer implementing stylistic rules that are obviated by automated formatting.

Note that Ruff and Black treat line-length enforcement a little differently. Black makes a
best-effort attempt to adhere to the `line-length`, but avoids automatic line-wrapping in some cases
(e.g., within comments). Ruff, on the other hand, will flag rule `E501` for any line that exceeds
the `line-length` setting. As such, if `E501` is enabled, Ruff can still trigger line-length
violations even when Black is enabled.
Note that Ruff's linter and Black treat line-length enforcement a little differently. Black, like
Ruff's formatter, makes a best-effort attempt to adhere to the
[`line-length`](settings.md#line-length), but avoids automatic line-wrapping in some cases (e.g.,
within comments). Ruff, on the other hand, will flag [`line-too-long`](rules/line-too-long.md)
(`E501`) for any line that exceeds the [`line-length`](settings.md#line-length) setting. As such, if
[`line-too-long`](rules/line-too-long.md) (`E501`) is enabled, Ruff can still trigger line-length
violations even when Black or `ruff format` is enabled.

## How does Ruff's formatter compare to Black?

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8 changes: 7 additions & 1 deletion docs/formatter.md
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Expand Up @@ -183,7 +183,7 @@ some rules that, when enabled, can cause conflicts with the formatter, leading t
behavior. When configured appropriately, the goal of Ruff's formatter-linter compatibility is
such that running the formatter should never introduce new lint errors.

As such, when using Ruff as a formatter, we recommend avoiding the following lint rules:
When using Ruff as a formatter, we recommend avoiding the following lint rules:

- [`tab-indentation`](rules/tab-indentation.md) (`W191`)
- [`indentation-with-invalid-multiple`](rules/indentation-with-invalid-multiple.md) (`E111`)
Expand All @@ -200,6 +200,11 @@ As such, when using Ruff as a formatter, we recommend avoiding the following lin
- [`single-line-implicit-string-concatenation`](rules/single-line-implicit-string-concatenation.md) (`ISC001`)
- [`multi-line-implicit-string-concatenation`](rules/multi-line-implicit-string-concatenation.md) (`ISC002`)

While the [`line-too-long`](rules/line-too-long.md) (`E501`) rule _can_ be used alongside the
formatter, the formatter only makes a best-effort attempt to wrap lines at the configured
[`line-length`](settings.md#line-length). As such, formatted code _may_ exceed the line length,
leading to [`line-too-long`](rules/line-too-long.md) (`E501`) errors.

None of the above are included in Ruff's default configuration. However, if you've enabled
any of these rules or their parent categories (like `Q`), we recommend disabling them via the
linter's [`ignore`](settings.md#ignore) setting.
Expand All @@ -216,6 +221,7 @@ formatter's treatment of import statements when set to non-default values:
If you've configured any of these settings to take on non-default values, we recommend removing
them from your Ruff configuration.


When an incompatible lint rule or setting is enabled, `ruff format` will emit a warning. If your
`ruff format` is free of warnings, you're good to go!

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