Handle backslashes in f-string interpolations for RUF027

Updated the RUF027 rule to only skip f-string suggestions for Python < 3.12 when backslashes appear in interpolations, not in the entire string. Adjusted test cases and snapshots to reflect this refined behavior.

crates/ruff_linter/resources/test/fixtures/ruff/RUF027_0.py

@@ -85,8 +85,8 @@ def in_type_def():
 def fuzz_bug():
     c('{\t"i}')
 
-# Test case for backslash handling in f-strings
-# Should not trigger RUF027 for Python < 3.12 due to backslashes
+# Test case for backslash handling in f-string interpolations
+# Should not trigger RUF027 for Python < 3.12 due to backslashes in interpolations
 def backslash_test():
     x = "test"
-    print("Hello {x}\\n")  # Should not trigger RUF027 for Python < 3.12
+    print("Hello {'\\n'}{x}")  # Should not trigger RUF027 for Python < 3.12

crates/ruff_linter/src/rules/ruff/rules/missing_fstring_syntax.rs

@@ -186,12 +186,6 @@ fn should_be_fstring(
         return false;
     }
 
-    // Check if the string contains backslashes and target Python version is < 3.12
-    // F-strings with backslashes are only valid in Python 3.12+
-    if literal.value.contains('\\') && checker.target_version() < PythonVersion::PY312 {
-        return false;
-    }
-
     let fstring_expr = format!("f{}", locator.slice(literal));
     let Ok(parsed) = parse_expression(&fstring_expr) else {
         return false;
@@ -223,6 +217,14 @@ fn should_be_fstring(
     for f_string in value.f_strings() {
         let mut has_name = false;
         for element in f_string.elements.interpolations() {
+            // Check if the interpolation expression contains backslashes
+            // F-strings with backslashes in interpolations are only valid in Python 3.12+
+            let interpolation_text = &fstring_expr[element.range()];
+            if interpolation_text.contains('\\') && checker.target_version() < PythonVersion::PY312
+            {
+                return false;
+            }
+
             if let ast::Expr::Name(ast::ExprName { id, .. }) = element.expression.as_ref() {
                 if arg_names.contains(id) {
                     return false;

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__RUF027_RUF027_0.py.snap

@@ -326,13 +326,13 @@ RUF027 [*] Possible f-string without an `f` prefix
    |
 90 | def backslash_test():
 91 |     x = "test"
-92 |     print("Hello {x}\\n")  # Should not trigger RUF027 for Python < 3.12
-   |           ^^^^^^^^^^^^^^
+92 |     print("Hello {'\\n'}{x}")  # Should not trigger RUF027 for Python < 3.12
+   |           ^^^^^^^^^^^^^^^^^^
    |
 help: Add `f` prefix
-89 | # Should not trigger RUF027 for Python < 3.12 due to backslashes
+89 | # Should not trigger RUF027 for Python < 3.12 due to backslashes in interpolations
 90 | def backslash_test():
 91 |     x = "test"
-   -     print("Hello {x}\\n")  # Should not trigger RUF027 for Python < 3.12
-92 +     print(f"Hello {x}\\n")  # Should not trigger RUF027 for Python < 3.12
+   -     print("Hello {'\\n'}{x}")  # Should not trigger RUF027 for Python < 3.12
+92 +     print(f"Hello {'\\n'}{x}")  # Should not trigger RUF027 for Python < 3.12
 note: This is an unsafe fix and may change runtime behavior