[ruff] Fix ISC003 autofix incorrectly stripping + from comments

crates/ruff_linter/resources/test/fixtures/flake8_implicit_str_concat/ISC.py

@@ -222,3 +222,20 @@
     "abc"
     "def"
 ) + "ghi"
+
+
+# https://github.com/astral-sh/ruff/issues/26541
+x = (
+    "A"  # Complains about this: +
+    + " broken"
+    + " line"
+    + " string."
+)
+
+foo(
+    bar="A"  # Complains about this: +
+    + " broken"
+    + " line"
+    + " string."
+)
+

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

@@ -1,5 +1,5 @@
 use ruff_macros::{ViolationMetadata, derive_message_formats};
-use ruff_python_ast::token::parenthesized_range;
+use ruff_python_ast::token::{TokenKind, parenthesized_range};
 use ruff_python_ast::{self as ast, Expr, Operator};
 use ruff_python_trivia::is_python_whitespace;
 use ruff_source_file::LineRanges;
@@ -116,7 +116,21 @@ fn generate_fix(checker: &Checker, expr_bin_op: &ast::ExprBinOp) -> Fix {
 
     let between_operands_range = TextRange::new(left.end(), right.start());
     let between_operands = checker.locator().slice(between_operands_range);
-    let (before_plus, after_plus) = between_operands.split_once('+').unwrap();
+
+    let plus_token = checker
+        .tokens()
+        .in_range(between_operands_range)
+        .iter()
+        .find(|token| token.kind() == TokenKind::Plus);
+
+    let (before_plus, after_plus) = if let Some(plus_token) = plus_token {
+        let plus_relative_start = plus_token.start() - left.end();
+        let (before, after) = between_operands.split_at(plus_relative_start.to_usize());
+        (before, &after[1..])
+    } else {
+        // Fallback in case of unexpected token structure
+        between_operands.split_once('+').unwrap()
+    };
 
     let linebreak_before_operator =
         before_plus.contains_line_break(TextRange::at(TextSize::new(0), before_plus.text_len()));

crates/ruff_linter/src/rules/flake8_implicit_str_concat/snapshots/ruff_linter__rules__flake8_implicit_str_concat__tests__ISC003_ISC.py.snap

@@ -351,3 +351,41 @@ ISC003 Explicitly concatenated string should be implicitly concatenated
     | |_________^
     |
 help: Remove redundant '+' operator to implicitly concatenate
+
+ISC003 [*] Explicitly concatenated string should be implicitly concatenated
+   --> ISC.py:229:5
+    |
+227 |   # https://github.com/astral-sh/ruff/issues/26541
+228 |   x = (
+229 | /     "A"  # Complains about this: +
+230 | |     + " broken"
+    | |_______________^
+231 |       + " line"
+232 |       + " string."
+    |
+help: Remove redundant '+' operator to implicitly concatenate
+    |
+229 |     "A"  # Complains about this: +
+    -     + " broken"
+230 +      " broken"
+231 |     + " line"
+    |
+
+ISC003 [*] Explicitly concatenated string should be implicitly concatenated
+   --> ISC.py:236:9
+    |
+235 |   foo(
+236 |       bar="A"  # Complains about this: +
+    |  _________^
+237 | |     + " broken"
+    | |_______________^
+238 |       + " line"
+239 |       + " string."
+    |
+help: Remove redundant '+' operator to implicitly concatenate
+    |
+236 |     bar="A"  # Complains about this: +
+    -     + " broken"
+237 +      " broken"
+238 |     + " line"
+    |