Use double quotes for all docstrings, including single-quoted docstrings (#9020)

crates/ruff_python_formatter/resources/test/fixtures/ruff/docstring.options.json

@@ -14,5 +14,8 @@
   {
     "indent_style": "tab",
     "indent_width": 4
+  },
+  {
+    "quote_style": "single"
   }
 ]

crates/ruff_python_formatter/resources/test/fixtures/ruff/docstring.py

@@ -150,3 +150,8 @@ class TabbedIndent:
 		Normal indented line
 		  	- autor
 		"""
+
+
+def single_quoted():
+    ' content\     '
+    return

crates/ruff_python_formatter/src/expression/string/mod.rs

@@ -213,7 +213,8 @@ impl<'a> Format<PyFormatContext<'_>> for FormatString<'a> {
                 let normalized = string_part.normalize(
                     Quoting::CanChange,
                     &locator,
-                    f.options().quote_style(),
+                    // Per PEP 8 and PEP 257, always prefer double quotes for docstrings
+                    QuoteStyle::Double,
                     parent_docstring_quote_style,
                 );
                 docstring::format(&normalized, f)
@@ -323,9 +324,7 @@ impl StringPart {
         configured_style: QuoteStyle,
         parent_docstring_quote_style: Option<QuoteStyle>,
     ) -> NormalizedString<'a> {
-        // Per PEP 8 and PEP 257, always prefer double quotes for docstrings
-        // and triple-quoted strings. (We assume docstrings are always
-        // triple-quoted.)
+        // Per PEP 8, always prefer double quotes for triple-quoted strings.
         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

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

@@ -156,6 +156,11 @@ class TabbedIndent:
 		Normal indented line
 		  	- autor
 		"""
+
+
+def single_quoted():
+    ' content\     '
+    return
 ```
 
 ## Outputs
@@ -324,6 +329,11 @@ class TabbedIndent:
         Normal indented line
                 - autor
         """
+
+
+def single_quoted():
+    "content\ "
+    return
 ```
 
 
@@ -492,6 +502,11 @@ class TabbedIndent:
     Normal indented line
             - autor
     """
+
+
+def single_quoted():
+  "content\ "
+  return
 ```
 
 
@@ -660,6 +675,11 @@ class TabbedIndent:
 		Normal indented line
 		        - autor
 		"""
+
+
+def single_quoted():
+	"content\ "
+	return
 ```
 
 
@@ -828,6 +848,184 @@ class TabbedIndent:
 		Normal indented line
 		        - autor
 		"""
+
+
+def single_quoted():
+	"content\ "
+	return
+```
+
+
+### Output 5
+```
+indent-style            = space
+line-width              = 88
+indent-width            = 4
+quote-style             = Single
+line-ending             = LineFeed
+magic-trailing-comma    = Respect
+docstring-code          = Disabled
+preview                 = Disabled
+```
+
+```python
+def single_line_backslashes1():
+    """content\ """
+    return
+
+
+def single_line_backslashes2():
+    """content\\"""
+    return
+
+
+def single_line_backslashes3():
+    """content\\\ """
+    return
+
+
+def multiline_backslashes1():
+    """This is a docstring with
+    some lines of text\ """
+    return
+
+
+def multiline_backslashes2():
+    """This is a docstring with
+    some lines of text\\"""
+    return
+
+
+def multiline_backslashes3():
+    """This is a docstring with
+    some lines of text\\\ """
+    return
+
+
+def multiple_negatively_indented_docstring_lines():
+    """a
+    b
+     c
+      d
+       e
+    """
+
+
+def overindentend_docstring():
+    """a
+    over-indented
+    """
+
+
+def comment_before_docstring():
+    # don't lose this function comment ...
+    """Does nothing.
+
+    But it has comments
+    """  # ... neither lose this function comment
+
+
+class CommentBeforeDocstring:
+    # don't lose this class comment ...
+    """Empty class.
+
+    But it has comments
+    """  # ... neither lose this class comment
+
+
+class IndentMeSome:
+    def doc_string_without_linebreak_after_colon(self):
+        """This is somewhat strange
+           a
+        b
+           We format this a is the docstring had started properly indented on the next
+           line if the target indentation. This may we incorrect since source and target
+           indentation can be incorrect, but this is also an edge case.
+        """
+
+
+class IgnoreImplicitlyConcatenatedStrings:
+    """""" ''
+
+
+def docstring_that_ends_with_quote_and_a_line_break1():
+    """
+    he said "the news of my death have been greatly exaggerated"
+    """
+
+
+def docstring_that_ends_with_quote_and_a_line_break2():
+    """he said "the news of my death have been greatly exaggerated" """
+
+
+def docstring_that_ends_with_quote_and_a_line_break3():
+    """he said "the news of my death have been greatly exaggerated" """
+
+
+class ByteDocstring:
+    b"""   has leading whitespace"""
+    first_statement = 1
+
+
+class CommentAfterDocstring1:
+    """Browse module classes and functions in IDLE."""
+
+    # This class is also the base class for pathbrowser.PathBrowser.
+
+    def __init__(self):
+        pass
+
+
+class CommentAfterDocstring2:
+    """Browse module classes and functions in IDLE."""
+
+    # This class is also the base class for pathbrowser.PathBrowser.
+
+    def __init__(self):
+        pass
+
+
+class CommentAfterDocstring3:
+    """Browse module classes and functions in IDLE."""
+
+    # This class is also the base class for pathbrowser.PathBrowser.
+    def __init__(self):
+        pass
+
+
+class CommentAfterDocstring4:
+    """Browse module classes and functions in IDLE."""
+
+    # This class is also the base class for pathbrowser.PathBrowser.
+    def __init__(self):
+        pass
+
+
+class CommentAfterDocstring5:
+    """Browse module classes and functions in IDLE."""
+
+    # This class is also the base class for pathbrowser.PathBrowser.
+
+
+def f():
+    """Browse module classes and functions in IDLE."""
+    # ^ Do not insert a newline above here
+
+    pass
+
+
+class TabbedIndent:
+    def tabbed_indent(self):
+        """check for correct tabbed formatting
+                                    ^^^^^^^^^^
+        Normal indented line
+                - autor
+        """
+
+
+def single_quoted():
+    "content\ "
+    return
 ```