Place 'r' prefix before 'f' for raw format strings

crates/ruff_linter/src/rules/pyupgrade/rules/f_strings.rs

@@ -191,15 +191,25 @@ fn try_convert_to_f_string(
     summary: &mut FormatSummaryValues,
     locator: &Locator,
 ) -> Result<Option<String>> {
+    let contents = locator.slice(range);
+
     // Strip the unicode prefix. It's redundant in Python 3, and invalid when used
     // with f-strings.
-    let contents = locator.slice(range);
     let contents = if contents.starts_with('U') || contents.starts_with('u') {
         &contents[1..]
     } else {
         contents
     };
 
+    // Temporarily strip the raw prefix, if present. It will be prepended to the result, before the
+    // 'f', to match the prefix order both the Ruff formatter (and Black) use when formatting code.
+    let raw = contents.starts_with('R') || contents.starts_with('r');
+    let contents = if raw {
+        &contents[1..]
+    } else {
+        contents
+    };
+
     // Remove the leading and trailing quotes.
     let leading_quote = leading_quote(contents).context("Unable to identify leading quote")?;
     let trailing_quote = trailing_quote(contents).context("Unable to identify trailing quote")?;
@@ -291,7 +301,10 @@ fn try_convert_to_f_string(
     }
 
     // Construct the format string.
-    let mut contents = String::with_capacity(1 + converted.len());
+    let mut contents = String::with_capacity(i32::from(raw) + 1 + converted.len());
+    if raw {
+        contents.push('r');
+    }
     contents.push('f');
     contents.push_str(leading_quote);
     contents.push_str(&converted);

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP032_0.py.snap

@@ -353,7 +353,7 @@ UP032_0.py:37:1: UP032 [*] Use f-string instead of `format` call
 35 35 | "foo{}".format(1)
 36 36 | 
 37    |-r"foo{}".format(1)
-   37 |+fr"foo{1}"
+   37 |+rf"foo{1}"
 38 38 | 
 39 39 | x = "{a}".format(a=1)
 40 40 |