fix: Avoid autofix for raw strings with \N escapes

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP032_0.py

@@ -276,5 +276,8 @@ if __name__ == "__main__":
     string = "{}".format(number := number + 1)
     print(string)
 
-# Unicode escape
+# Unicode escape in regular string, should convert.
 "\N{angle}AOB = {angle}°".format(angle=180)
+
+# Unicode escape in raw string, should not convert - would change semantics.
+r"\N{angle}AOB = {angle}°".format(angle=180)

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

@@ -229,6 +229,9 @@ enum FStringConversion {
     /// The format call uses arguments with side effects which are repeated within the
     /// format string. For example: `"{x} {x}".format(x=foo())`.
     SideEffects,
+    /// The format string is a raw string containing `\N{...}` which would be
+    /// misinterpreted in an f-string.
+    UnsafeRawString,
     /// The format string should be converted to an f-string.
     Convert(String),
 }
@@ -286,6 +289,15 @@ impl FStringConversion {
             return Ok(Self::NonEmptyLiteral);
         }
 
+        // `\N{...}` is literal in raw strings but becomes a Unicode escape in f-strings.
+        if raw
+            && format_string.format_parts.iter().any(
+                |part| matches!(part, FormatPart::Literal(literal) if literal.contains("\\N{")),
+            )
+        {
+            return Ok(Self::UnsafeRawString);
+        }
+
         let mut converted = String::with_capacity(contents.len());
         let mut seen = FxHashSet::default();
         for part in format_string.format_parts {
@@ -416,6 +428,7 @@ pub(crate) fn f_strings(checker: &Checker, call: &ast::ExprCall, summary: &Forma
 
     let mut patches: Vec<(TextRange, FStringConversion)> = vec![];
     let mut tokens = checker.tokens().in_range(call.func.range()).iter();
+    let mut unsafe_conversion = false;
     let end = loop {
         let Some(token) = tokens.next() else {
             unreachable!("Should break from the `Tok::Dot` arm");
@@ -441,6 +454,11 @@ pub(crate) fn f_strings(checker: &Checker, call: &ast::ExprCall, summary: &Forma
                     // If the format string contains side effects that would need to be repeated,
                     // we can't convert it to an f-string.
                     Ok(FStringConversion::SideEffects) => return,
+                    // If the format string is a raw string with `\N{...}`, conversion would be unsafe.
+                    // We still want to emit the diagnostic, but without offering a fix.
+                    Ok(FStringConversion::UnsafeRawString) => {
+                        unsafe_conversion = true;
+                    }
                     // If any of the segments fail to convert, then we can't convert the entire
                     // expression.
                     Err(_) => return,
@@ -451,7 +469,7 @@ pub(crate) fn f_strings(checker: &Checker, call: &ast::ExprCall, summary: &Forma
             _ => {}
         }
     };
-    if patches.is_empty() {
+    if patches.is_empty() && !unsafe_conversion {
         return;
     }
 
@@ -466,7 +484,7 @@ pub(crate) fn f_strings(checker: &Checker, call: &ast::ExprCall, summary: &Forma
                 Some(curly_unescape(checker.locator().slice(range)).to_string())
             }
             // We handled this in the previous loop.
-            FStringConversion::SideEffects => unreachable!(),
+            FStringConversion::SideEffects | FStringConversion::UnsafeRawString => unreachable!(),
         };
         if let Some(fstring) = fstring {
             contents.push_str(
@@ -520,7 +538,7 @@ pub(crate) fn f_strings(checker: &Checker, call: &ast::ExprCall, summary: &Forma
     // ```
     let has_comments = checker.comment_ranges().intersects(call.arguments.range());
 
-    if !has_comments {
+    if !has_comments && !unsafe_conversion {
         if contents.is_empty() {
             // Ex) `''.format(self.project)`
             diagnostic.set_fix(Fix::safe_edit(Edit::range_replacement(

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

@@ -1370,18 +1370,32 @@ help: Convert to f-string
 276 +     string = f"{(number := number + 1)}"
 277 |     print(string)
 278 | 
-279 | # Unicode escape
+279 | # Unicode escape in regular string, should convert.
 
 UP032 [*] Use f-string instead of `format` call
    --> UP032_0.py:280:1
     |
-279 | # Unicode escape
+279 | # Unicode escape in regular string, should convert.
 280 | "\N{angle}AOB = {angle}°".format(angle=180)
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+281 |
+282 | # Unicode escape in raw string, should not convert - would change semantics.
     |
 help: Convert to f-string
 277 |     print(string)
 278 | 
-279 | # Unicode escape
+279 | # Unicode escape in regular string, should convert.
     - "\N{angle}AOB = {angle}°".format(angle=180)
 280 + f"\N{angle}AOB = {180}°"
+281 | 
+282 | # Unicode escape in raw string, should not convert - would change semantics.
+283 | r"\N{angle}AOB = {angle}°".format(angle=180)
+
+UP032 Use f-string instead of `format` call
+   --> UP032_0.py:283:1
+    |
+282 | # Unicode escape in raw string, should not convert - would change semantics.
+283 | r"\N{angle}AOB = {angle}°".format(angle=180)
+    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+    |
+help: Convert to f-string