Stabilize quote-style preserve (#9922)

crates/ruff_python_formatter/src/options.rs

@@ -248,6 +248,12 @@ pub enum QuoteStyle {
     Preserve,
 }
 
+impl QuoteStyle {
+    pub const fn is_preserve(self) -> bool {
+        matches!(self, QuoteStyle::Preserve)
+    }
+}
+
 impl fmt::Display for QuoteStyle {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {

crates/ruff_python_formatter/src/other/string_literal.rs

@@ -50,11 +50,13 @@ impl Format<PyFormatContext<'_>> for FormatStringLiteral<'_> {
     fn fmt(&self, f: &mut PyFormatter) -> FormatResult<()> {
         let locator = f.context().locator();
 
-        let quote_style = if self.layout.is_docstring() {
-            // Per PEP 8 and PEP 257, always prefer double quotes for docstrings
+        let quote_style = f.options().quote_style();
+        let quote_style = if self.layout.is_docstring() && !quote_style.is_preserve() {
+            // Per PEP 8 and PEP 257, always prefer double quotes for docstrings,
+            // except when using quote-style=preserve
             QuoteStyle::Double
         } else {
-            f.options().quote_style()
+            quote_style
         };
 
         let normalized = StringPart::from_source(self.value.range(), &locator).normalize(

crates/ruff_python_formatter/src/string/mod.rs

@@ -306,6 +306,7 @@ impl StringPart {
         normalize_hex: bool,
     ) -> NormalizedString<'a> {
         // Per PEP 8, always prefer double quotes for triple-quoted strings.
+        // Except when using quote-style-preserve.
         let preferred_style = if self.quotes.triple {
             // ... unless we're formatting a code snippet inside a docstring,
             // then we specifically want to invert our quote style to avoid
@@ -354,6 +355,8 @@ impl StringPart {
             // if it doesn't have perfect alignment with PEP8.
             if let Some(quote) = parent_docstring_quote_char {
                 QuoteStyle::from(quote.invert())
+            } else if configured_style.is_preserve() {
+                QuoteStyle::Preserve
             } else {
                 QuoteStyle::Double
             }

crates/ruff_python_formatter/tests/snapshots/format@quote_style.py.snap

@@ -263,21 +263,21 @@ rb"rb double"
 rb'br single'
 rb"br double"
 
-"""single triple"""
+'''single triple'''
 """double triple"""
-r"""r single triple"""
+r'''r single triple'''
 r"""r double triple"""
-f"""f single triple"""
+f'''f single triple'''
 f"""f double triple"""
-rf"""fr single triple"""
+rf'''fr single triple'''
 rf"""fr double triple"""
-rf"""rf single triple"""
+rf'''rf single triple'''
 rf"""rf double triple"""
-b"""b single triple"""
+b'''b single triple'''
 b"""b double triple"""
-rb"""rb single triple"""
+rb'''rb single triple'''
 rb"""rb double triple"""
-rb"""br single triple"""
+rb'''br single triple'''
 rb"""br double triple"""
 
 'single1' 'single2'
@@ -287,7 +287,7 @@ rb"""br double triple"""
 
 
 def docstring_single_triple():
-    """single triple"""
+    '''single triple'''
 
 
 def docstring_double_triple():
@@ -299,7 +299,7 @@ def docstring_double():
 
 
 def docstring_single():
-    "single"
+    'single'
 ```
 
 
@@ -308,8 +308,7 @@ def docstring_single():
 --- Stable
 +++ Preview
 @@ -1,4 +1,5 @@
--'single'  # this string is treated as a docstring
-+"single"  # this string is treated as a docstring
+ 'single'  # this string is treated as a docstring
 +
  "double"
  r'r single'