Alternate quotes for strings inside f-strings in preview (#13860)

crates/ruff_dev/src/format_dev.rs

@@ -251,8 +251,7 @@ pub(crate) fn main(args: &Args) -> anyhow::Result<ExitCode> {
         }
         info!(
             parent: None,
-            "Done: {} stability errors, {} files, similarity index {:.5}), files with differences: {} took {:.2}s, {} input files contained syntax errors ",
-            error_count,
+            "Done: {error_count} stability/syntax errors, {} files, similarity index {:.5}), files with differences: {} took {:.2}s, {} input files contained syntax errors ",
             result.file_count,
             result.statistics.similarity_index(),
             result.statistics.files_with_differences,
@@ -796,7 +795,7 @@ impl CheckFileError {
             | CheckFileError::PrintError(_)
             | CheckFileError::Panic { .. } => false,
             #[cfg(not(debug_assertions))]
-            CheckFileError::Slow(_) => false,
+            CheckFileError::Slow(_) => true,
         }
     }
 }

crates/ruff_python_ast/src/expression.rs

@@ -524,6 +524,10 @@ impl StringLikePart<'_> {
             self.end() - kind.closer_len(),
         )
     }
+
+    pub const fn is_fstring(self) -> bool {
+        matches!(self, Self::FString(_))
+    }
 }
 
 impl<'a> From<&'a ast::StringLiteral> for StringLikePart<'a> {

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/fstring.py

@@ -94,6 +94,8 @@
                                              "bbbbbbbbbbbbbbbbbbbbbbbbbbbbb" } ccccccccccccccc"
 x = f"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa { # comment 9
                                              "bbbbbbbbbbbbbbbbbbbbbbbbbbbbb" = } ccccccccccccccc"
+x = f"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa { # comment 9
+                                             'bbbbbbbbbbbbbbbbbbbbbbbbbbbbb' = } ccccccccccccccc"
 
 # Multiple larger expressions which exceeds the line length limit. Here, we need to decide
 # whether to split at the first or second expression. This should work similarly to the
@@ -144,18 +146,37 @@
     {'aaaaaaaaaaaaaaaaaaaaaaaaa', 'bbbbbbbbbbbbbbbbbbbbbbbbbbb', 'cccccccccccccccccccccccccc'}
 }"
 
+#############################################################################################
 # Quotes
+#############################################################################################
 f"foo 'bar' {x}"
 f"foo \"bar\" {x}"
 f'foo "bar" {x}'
 f'foo \'bar\' {x}'
 f"foo {"bar"}"
-f"foo {'\'bar\''}"
+
+f"single quoted '{x}' double quoted \"{x}\"" # Same number of quotes => use preferred quote style
+f"single quote ' {x} double quoted \"{x}\""  # More double quotes => use single quotes
+f"single quoted '{x}' double quote \" {x}"  # More single quotes => use double quotes
+
+fr"single quotes ' {x}"  # Keep double because `'` can't be escaped
+fr'double quotes " {x}'  # Keep single because `"` can't be escaped
+fr'flip quotes {x}'  # Use preferred quotes, because raw string contains now quotes.
 
 # Here, the formatter will remove the escapes which is correct because they aren't allowed
 # pre 3.12. This means we can assume that the f-string is used in the context of 3.12.
+f"foo {'\'bar\''}"
 f"foo {'\"bar\"'}"
 
+# Quotes inside the expressions have no impact on the quote selection of the outer string.
+# Required so that the following two examples result in the same formatting.
+f'foo {10 + len("bar")}'
+f"foo {10 + len('bar')}"
+
+# Pre 312, preserve the outer quotes if the f-string contains quotes in the debug expression
+f'foo {10 + len("bar")=}'
+f'''foo {10 + len('''bar''')=}'''
+f'''foo {10 + len('bar')=}'''  # Fine to change the quotes because it uses triple quotes
 
 # Triple-quoted strings
 # It's ok to use the same quote char for the inner string if it's single-quoted.
@@ -164,6 +185,16 @@
 # But if the inner string is also triple-quoted then we should preserve the existing quotes.
 f"""test {'''inner'''}"""
 
+# It's not okay to change the quote style if the inner string is triple quoted and contains a quote.
+f'{"""other " """}'
+f'{"""other " """ + "more"}'
+f'{b"""other " """}'
+f'{f"""other " """}'
+
+# Not valid Pre 3.12
+f"""test {f'inner {'''inner inner'''}'}"""
+f"""test {f'''inner {"""inner inner"""}'''}"""
+
 # Magic trailing comma
 #
 # The expression formatting will result in breaking it across multiple lines with a
@@ -312,6 +343,6 @@
 # Implicit concatenated f-string containing quotes
 _ = (
     'This string should change its quotes to double quotes'
-    f'This string uses double quotes in an expression {"woah"}'
+    f'This string uses double quotes in an expression {"it's a quote"}'
     f'This f-string does not use any quotes.'
 )

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/fstring_py312.py

@@ -4,3 +4,14 @@
 
 # Quotes reuse
 f"{'a'}"
+
+# 312+, it's okay to change the outer quotes even when there's a debug expression using the same quotes
+f'foo {10 + len("bar")=}'
+f'''foo {10 + len("""bar""")=}'''
+
+# 312+, it's okay to change the quotes here without creating an invalid f-string
+f'{"""other " """}'
+f'{"""other " """ + "more"}'
+f'{b"""other " """}'
+f'{f"""other " """}'
+

crates/ruff_python_formatter/src/other/f_string.rs

@@ -1,12 +1,12 @@
+use ruff_formatter::write;
+use ruff_python_ast::{AnyStringFlags, FString, StringFlags};
+use ruff_source_file::Locator;
+
 use crate::prelude::*;
 use crate::preview::{
     is_f_string_formatting_enabled, is_f_string_implicit_concatenated_string_literal_quotes_enabled,
 };
 use crate::string::{Quoting, StringNormalizer, StringQuotes};
-use ruff_formatter::write;
-use ruff_python_ast::{AnyStringFlags, FString, StringFlags};
-use ruff_source_file::Locator;
-use ruff_text_size::Ranged;
 
 use super::f_string_element::FormatFStringElement;
 
@@ -35,7 +35,7 @@ impl Format<PyFormatContext<'_>> for FormatFString<'_> {
         // f-string instead of globally for the entire f-string expression.
         let quoting =
             if is_f_string_implicit_concatenated_string_literal_quotes_enabled(f.context()) {
-                f_string_quoting(self.value, &locator)
+                Quoting::CanChange
             } else {
                 self.quoting
             };
@@ -92,17 +92,21 @@ impl Format<PyFormatContext<'_>> for FormatFString<'_> {
 
 #[derive(Clone, Copy, Debug)]
 pub(crate) struct FStringContext {
-    flags: AnyStringFlags,
+    /// The string flags of the enclosing f-string part.
+    enclosing_flags: AnyStringFlags,
     layout: FStringLayout,
 }
 
 impl FStringContext {
     const fn new(flags: AnyStringFlags, layout: FStringLayout) -> Self {
-        Self { flags, layout }
+        Self {
+            enclosing_flags: flags,
+            layout,
+        }
     }
 
     pub(crate) fn flags(self) -> AnyStringFlags {
-        self.flags
+        self.enclosing_flags
     }
 
     pub(crate) const fn layout(self) -> FStringLayout {
@@ -149,20 +153,3 @@ impl FStringLayout {
         matches!(self, FStringLayout::Multiline)
     }
 }
-
-fn f_string_quoting(f_string: &FString, locator: &Locator) -> Quoting {
-    let triple_quoted = f_string.flags.is_triple_quoted();
-
-    if f_string.elements.expressions().any(|expression| {
-        let string_content = locator.slice(expression.range());
-        if triple_quoted {
-            string_content.contains(r#"""""#) || string_content.contains("'''")
-        } else {
-            string_content.contains(['"', '\''])
-        }
-    }) {
-        Quoting::Preserve
-    } else {
-        Quoting::CanChange
-    }
-}

crates/ruff_python_formatter/src/other/f_string_element.rs

@@ -2,8 +2,8 @@ use std::borrow::Cow;
 
 use ruff_formatter::{format_args, write, Buffer, RemoveSoftLinesBuffer};
 use ruff_python_ast::{
-    ConversionFlag, Expr, FStringElement, FStringExpressionElement, FStringLiteralElement,
-    StringFlags,
+    AnyStringFlags, ConversionFlag, Expr, FStringElement, FStringExpressionElement,
+    FStringLiteralElement, StringFlags,
 };
 use ruff_text_size::Ranged;
 
@@ -33,7 +33,7 @@ impl Format<PyFormatContext<'_>> for FormatFStringElement<'_> {
     fn fmt(&self, f: &mut PyFormatter) -> FormatResult<()> {
         match self.element {
             FStringElement::Literal(string_literal) => {
-                FormatFStringLiteralElement::new(string_literal, self.context).fmt(f)
+                FormatFStringLiteralElement::new(string_literal, self.context.flags()).fmt(f)
             }
             FStringElement::Expression(expression) => {
                 FormatFStringExpressionElement::new(expression, self.context).fmt(f)
@@ -45,19 +45,23 @@ impl Format<PyFormatContext<'_>> for FormatFStringElement<'_> {
 /// Formats an f-string literal element.
 pub(crate) struct FormatFStringLiteralElement<'a> {
     element: &'a FStringLiteralElement,
-    context: FStringContext,
+    /// Flags of the enclosing F-string part
+    fstring_flags: AnyStringFlags,
 }
 
 impl<'a> FormatFStringLiteralElement<'a> {
-    pub(crate) fn new(element: &'a FStringLiteralElement, context: FStringContext) -> Self {
-        Self { element, context }
+    pub(crate) fn new(element: &'a FStringLiteralElement, fstring_flags: AnyStringFlags) -> Self {
+        Self {
+            element,
+            fstring_flags,
+        }
     }
 }
 
 impl Format<PyFormatContext<'_>> for FormatFStringLiteralElement<'_> {
     fn fmt(&self, f: &mut PyFormatter) -> FormatResult<()> {
         let literal_content = f.context().locator().slice(self.element.range());
-        let normalized = normalize_string(literal_content, 0, self.context.flags(), true);
+        let normalized = normalize_string(literal_content, 0, self.fstring_flags, true);
         match &normalized {
             Cow::Borrowed(_) => source_text_slice(self.element.range()).fmt(f),
             Cow::Owned(normalized) => text(normalized).fmt(f),

crates/ruff_python_formatter/src/preview.rs

@@ -15,11 +15,13 @@ pub(crate) const fn is_hug_parens_with_braces_and_square_brackets_enabled(
 }
 
 /// Returns `true` if the [`f-string formatting`](https://github.com/astral-sh/ruff/issues/7594) preview style is enabled.
+/// WARNING: This preview style depends on `is_f_string_implicit_concatenated_string_literal_quotes_enabled`.
 pub(crate) fn is_f_string_formatting_enabled(context: &PyFormatContext) -> bool {
     context.is_preview()
 }
 
 /// See [#13539](https://github.com/astral-sh/ruff/pull/13539)
+/// Remove `Quoting` when stabalizing this preview style.
 pub(crate) fn is_f_string_implicit_concatenated_string_literal_quotes_enabled(
     context: &PyFormatContext,
 ) -> bool {