Remove formatter incompatibility warning for ISC001

crates/ruff/src/commands/format.rs

@@ -233,7 +233,7 @@ pub(crate) fn format(
 }
 
 /// Format the file at the given [`Path`].
-#[tracing::instrument(level="debug", skip_all, fields(path = %path.display()))]
+#[tracing::instrument(level = "debug", skip_all, fields(path = %path.display()))]
 pub(crate) fn format_path(
     path: &Path,
     settings: &FormatterSettings,
@@ -788,8 +788,6 @@ pub(super) fn warn_incompatible_formatter_settings(resolver: &Resolver) {
     let mut incompatible_rules = FxHashSet::default();
     for setting in resolver.settings() {
         for rule in [
-            // The formatter might collapse implicit string concatenation on a single line.
-            Rule::SingleLineImplicitStringConcatenation,
             // Flags missing trailing commas when all arguments are on its own line:
             // ```python
             // def args(
@@ -829,6 +827,19 @@ pub(super) fn warn_incompatible_formatter_settings(resolver: &Resolver) {
             warn_user_once!("The `format.indent-style=\"tab\"` option is incompatible with `W191`, which lints against all uses of tabs. We recommend disabling these rules when using the formatter, which enforces a consistent indentation style. Alternatively, set the `format.indent-style` option to `\"space\"`.");
         }
 
+        if !setting
+            .linter
+            .rules
+            .enabled(Rule::SingleLineImplicitStringConcatenation)
+            && setting
+                .linter
+                .rules
+                .enabled(Rule::MultiLineImplicitStringConcatenation)
+            && !setting.linter.flake8_implicit_str_concat.allow_multiline
+        {
+            warn_user_once!("The `lint.flake8-implicit-str-concat.allow-multiline = false` option is incompatible with the formatter unless `ISC001` is enabled. We recommend enabling `ISC001` or setting `allow-multiline=true`.");
+        }
+
         // Validate all rules that rely on tab styles.
         if setting.linter.rules.enabled(Rule::DocstringTabIndentation)
             && setting.formatter.indent_style.is_tab()

crates/ruff/tests/format.rs

@@ -877,7 +877,7 @@ indent-width = 2
 
 [lint]
 select = ["ALL"]
-ignore = ["D203", "D212"]
+ignore = ["D203", "D212", "ISC001"]
 
 [lint.isort]
 lines-after-imports = 3
@@ -891,6 +891,9 @@ inline-quotes = "single"
 docstring-quotes = "single"
 multiline-quotes = "single"
 
+[lint.flake8-implicit-str-concat]
+allow-multiline = false
+
 [format]
 skip-magic-trailing-comma = true
 indent-style = "tab"
@@ -915,8 +918,9 @@ def say_hy(name: str):
     1 file reformatted
 
     ----- stderr -----
-    warning: The following rules may cause conflicts when used with the formatter: `COM812`, `ISC001`. To avoid unexpected behavior, we recommend disabling these rules, either by removing them from the `select` or `extend-select` configuration, or adding them to the `ignore` configuration.
+    warning: The following rule may cause conflicts when used with the formatter: `COM812`. To avoid unexpected behavior, we recommend disabling this rule, either by removing it from the `select` or `extend-select` configuration, or adding it to the `ignore` configuration.
     warning: The `format.indent-style="tab"` option is incompatible with `W191`, which lints against all uses of tabs. We recommend disabling these rules when using the formatter, which enforces a consistent indentation style. Alternatively, set the `format.indent-style` option to `"space"`.
+    warning: The `lint.flake8-implicit-str-concat.allow-multiline = false` option is incompatible with the formatter unless `ISC001` is enabled. We recommend enabling `ISC001` or setting `allow-multiline=true`.
     warning: The `format.indent-style="tab"` option is incompatible with `D206`, with requires space-based indentation. We recommend disabling these rules when using the formatter, which enforces a consistent indentation style. Alternatively, set the `format.indent-style` option to `"space"`.
     warning: The `flake8-quotes.inline-quotes="single"` option is incompatible with the formatter's `format.quote-style="double"`. We recommend disabling `Q000` and `Q003` when using the formatter, which enforces a consistent quote style. Alternatively, set both options to either `"single"` or `"double"`.
     warning: The `flake8-quotes.multiline-quotes="single"` option is incompatible with the formatter. We recommend disabling `Q001` when using the formatter, which enforces double quotes for multiline strings. Alternatively, set the `flake8-quotes.multiline-quotes` option to `"double"`.`
@@ -974,7 +978,7 @@ def say_hy(name: str):
     	print(f"Hy {name}")
 
     ----- stderr -----
-    warning: The following rules may cause conflicts when used with the formatter: `COM812`, `ISC001`. To avoid unexpected behavior, we recommend disabling these rules, either by removing them from the `select` or `extend-select` configuration, or adding them to the `ignore` configuration.
+    warning: The following rule may cause conflicts when used with the formatter: `COM812`. To avoid unexpected behavior, we recommend disabling this rule, either by removing it from the `select` or `extend-select` configuration, or adding it to the `ignore` configuration.
     warning: The `format.indent-style="tab"` option is incompatible with `W191`, which lints against all uses of tabs. We recommend disabling these rules when using the formatter, which enforces a consistent indentation style. Alternatively, set the `format.indent-style` option to `"space"`.
     warning: The `format.indent-style="tab"` option is incompatible with `D206`, with requires space-based indentation. We recommend disabling these rules when using the formatter, which enforces a consistent indentation style. Alternatively, set the `format.indent-style` option to `"space"`.
     warning: The `flake8-quotes.inline-quotes="single"` option is incompatible with the formatter's `format.quote-style="double"`. We recommend disabling `Q000` and `Q003` when using the formatter, which enforces a consistent quote style. Alternatively, set both options to either `"single"` or `"double"`.
@@ -1114,7 +1118,7 @@ def say_hy(name: str):
     ----- stderr -----
     warning: `incorrect-blank-line-before-class` (D203) and `no-blank-line-before-class` (D211) are incompatible. Ignoring `incorrect-blank-line-before-class`.
     warning: `multi-line-summary-first-line` (D212) and `multi-line-summary-second-line` (D213) are incompatible. Ignoring `multi-line-summary-second-line`.
-    warning: The following rules may cause conflicts when used with the formatter: `COM812`, `ISC001`. To avoid unexpected behavior, we recommend disabling these rules, either by removing them from the `select` or `extend-select` configuration, or adding them to the `ignore` configuration.
+    warning: The following rule may cause conflicts when used with the formatter: `COM812`. To avoid unexpected behavior, we recommend disabling this rule, either by removing it from the `select` or `extend-select` configuration, or adding it to the `ignore` configuration.
     ");
     Ok(())
 }

crates/ruff_linter/src/rules/flake8_implicit_str_concat/rules/implicit.rs

@@ -34,21 +34,6 @@ use crate::Locator;
 /// ```python
 /// z = "The quick brown fox."
 /// ```
-///
-/// # Formatter compatibility
-/// Use of this rule alongside the [formatter] must be handled with care.
-/// Currently, the [formatter] can introduce new single-line implicitly
-/// concatenated strings, therefore we suggest rerunning the linter and
-/// [formatter] in the following order:
-/// 1. Run the linter with this rule (`ISC001`) disabled
-/// 2. Run the [formatter]
-/// 3. Rerun the linter with this rule (`ISC001`) enabled
-///
-/// This is one of very few cases where the [formatter] can produce code that
-/// contains lint violations. It is a known issue that should be resolved by the
-/// new 2025 style guide.
-///
-/// [formatter]:https://docs.astral.sh/ruff/formatter/
 #[derive(ViolationMetadata)]
 pub(crate) struct SingleLineImplicitStringConcatenation;
 
@@ -96,19 +81,13 @@ impl Violation for SingleLineImplicitStringConcatenation {
 /// ## Options
 /// - `lint.flake8-implicit-str-concat.allow-multiline`
 ///
-/// # Formatter compatibility
-/// Use of this rule alongside the [formatter] must be handled with care.
-/// Currently, the [formatter] can introduce new multi-line implicitly
-/// concatenated strings, therefore we suggest rerunning the linter and
-/// [formatter] in the following order:
-///
-/// 1. Run the linter with this rule (`ISC002`) disabled
-/// 2. Run the [formatter]
-/// 3. Rerun the linter with this rule (`ISC002`) enabled
+/// ## Formatter compatibility
+/// Using this rule with `allow-multiline = false` can be incompatible with the
+/// formatter because the [formatter] can introduce new multi-line implicitly
+/// concatenated strings. We recommend to either:
 ///
-/// This is one of very few cases where the [formatter] can produce code that
-/// contains lint violations. It is a known issue that should be resolved by the
-/// new 2025 style guide.
+/// * Enable `ISC001` to disallow all implicit concatenated strings
+/// * Setting `allow-multiline = true`
 ///
 /// [PEP 8]: https://peps.python.org/pep-0008/#maximum-line-length
 /// [formatter]:https://docs.astral.sh/ruff/formatter/

docs/formatter.md

@@ -330,8 +330,7 @@ When using Ruff as a formatter, we recommend avoiding the following lint rules:
 - [`avoidable-escaped-quote`](rules/avoidable-escaped-quote.md) (`Q003`)
 - [`missing-trailing-comma`](rules/missing-trailing-comma.md) (`COM812`)
 - [`prohibited-trailing-comma`](rules/prohibited-trailing-comma.md) (`COM819`)
-- [`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`)
+- [`multi-line-implicit-string-concatenation`](rules/multi-line-implicit-string-concatenation.md) (`ISC002`) if used without `ISC001` and `flake8-implicit-str-concat.allow-multiline = false`
 
 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