fix(css_formatter): keep @charset double quote in single quote config

crates/biome_css_formatter/src/css/auxiliary/attribute_matcher_value.rs

@@ -1,4 +1,4 @@
-use crate::{prelude::*, utils::string_utils::FormatLiteralStringToken};
+use crate::{prelude::*, utils::string_utils::{ FormatLiteralStringToken, StringLiteralParentKind}};
 use biome_css_syntax::{
     AnyCssAttributeMatcherValue, CssAttributeMatcherValue, CssAttributeMatcherValueFields,
 };
@@ -35,7 +35,7 @@ impl FormatNodeRule<CssAttributeMatcherValue> for FormatCssAttributeMatcherValue
                         // does not get converted to lowercase. Once it's quoted, it
                         // will be parsed as a CssString on the next pass, at which
                         // point casing is preserved no matter what.
-                        FormatLiteralStringToken::new(&ident.value_token()?),
+                        FormatLiteralStringToken::new(&ident.value_token()?, StringLiteralParentKind::Others),
                         format_trailing_comments(ident.syntax()),
                         format_dangling_comments(ident.syntax())
                     ]

crates/biome_css_formatter/src/css/value/string.rs

@@ -1,13 +1,17 @@
-use crate::{prelude::*, utils::string_utils::FormatLiteralStringToken};
-use biome_css_syntax::{CssString, CssStringFields};
+use crate::{prelude::*, utils::string_utils::{FormatLiteralStringToken, StringLiteralParentKind}};
+use biome_css_syntax::{CssString, CssStringFields, CssSyntaxKind};
 use biome_formatter::write;
+use biome_rowan::SyntaxNodeOptionExt;
 
 #[derive(Debug, Clone, Default)]
 pub(crate) struct FormatCssString;
 impl FormatNodeRule<CssString> for FormatCssString {
     fn fmt_fields(&self, node: &CssString, f: &mut CssFormatter) -> FormatResult<()> {
         let CssStringFields { value_token } = node.as_fields();
-
-        write!(f, [FormatLiteralStringToken::new(&value_token?)])
+        if matches!(node.syntax().parent().kind(), Some(CssSyntaxKind::CSS_CHARSET_AT_RULE)) {
+            write!(f, [FormatLiteralStringToken::new(&value_token?, StringLiteralParentKind::CharsetAtRule)])
+        } else {
+            write!(f, [FormatLiteralStringToken::new(&value_token?, StringLiteralParentKind::Others)])
+        }
     }
 }

crates/biome_css_formatter/src/utils/string_utils.rs

@@ -43,17 +43,29 @@ impl Format<CssFormatContext> for FormatTokenAsLowercase {
     }
 }
 
+#[derive(Eq, PartialEq, Debug)]
+pub(crate) enum StringLiteralParentKind {
+    /// Variants to track tokens that are inside a CssCharasetRule
+    /// @charset must always have double quotes: https://www.w3.org/TR/css-syntax-3/#determine-the-fallback-encoding
+    CharsetAtRule,
+    /// other types, will add more later
+    Others
+}
+
 /// Data structure of convenience to format string literals. This is copied
 /// from the JS formatter, but should eventually have the logic made generic
 /// and reusable since many languages will have the same needs.
 pub(crate) struct FormatLiteralStringToken<'token> {
     /// The current token
     token: &'token CssSyntaxToken,
+
+    // The parent that holds the token
+    parent_kind: StringLiteralParentKind
 }
 
 impl<'token> FormatLiteralStringToken<'token> {
-    pub fn new(token: &'token CssSyntaxToken) -> Self {
-        Self { token }
+    pub fn new(token: &'token CssSyntaxToken, parent_kind: StringLiteralParentKind) -> Self {
+        Self { token, parent_kind }
     }
 
     fn token(&self) -> &'token CssSyntaxToken {
@@ -204,18 +216,31 @@ impl<'token> LiteralStringNormaliser<'token> {
     }
 
     fn normalise_text(&mut self) -> Cow<'token, str> {
-        let string_information = self
-            .token
-            .compute_string_information(self.chosen_quote_style);
-
-        // Normalize string token and non-string token.
-        //
-        // Add the chosen quotes to any non-string tokensto normalize them into strings.
-        //
-        // CSS has various places where "string-like" tokens can be used without quotes, but the
-        // semantics aren't affected by whether they are present or not. This function lets those
-        // tokens become string literals by safely adding quotes around them.
-        self.normalise_tokens(string_information)
+
+        match self.token.parent_kind {
+            StringLiteralParentKind::CharsetAtRule => {
+                let string_information = StringInformation {
+                    preferred_quote: QuoteStyle::Double,
+                };
+                self.normalise_tokens(string_information)
+            },
+            StringLiteralParentKind::Others => {
+                let string_information = self
+                    .token
+                    .compute_string_information(self.chosen_quote_style);
+
+                // Normalize string token and non-string token.
+                //
+                // Add the chosen quotes to any non-string tokensto normalize them into strings.
+                //
+                // CSS has various places where "string-like" tokens can be used without quotes, but the
+                // semantics aren't affected by whether they are present or not. This function lets those
+                // tokens become string literals by safely adding quotes around them.
+                self.normalise_tokens(string_information)
+            }
+        }
+
+
     }
 
     fn get_token(&self) -> &'token CssSyntaxToken {

crates/biome_css_formatter/tests/quick_test.rs

@@ -1,7 +1,7 @@
 use biome_css_formatter::format_node;
 use biome_css_formatter::{context::CssFormatOptions, CssFormatLanguage};
 use biome_css_parser::{parse_css, CssParserOptions};
-use biome_formatter::{IndentStyle, LineWidth};
+use biome_formatter::{IndentStyle, LineWidth, QuoteStyle};
 use biome_formatter_test::check_reformat::CheckReformat;
 
 mod language {
@@ -13,18 +13,15 @@ mod language {
 // use this test check if your snippet prints as you wish, without using a snapshot
 fn quick_test() {
     let src = r#"
-.container {
-  &:has(.child) {
-    color: blue;
-  }
-}
+@charset "UTF-8";
 "#;
     let parse = parse_css(src, CssParserOptions::default());
     println!("{parse:#?}");
 
     let options = CssFormatOptions::default()
         .with_line_width(LineWidth::try_from(80).unwrap())
-        .with_indent_style(IndentStyle::Space);
+        .with_indent_style(IndentStyle::Space)
+        .with_quote_style(QuoteStyle::Single);
     let doc = format_node(options.clone(), &parse.syntax()).unwrap();
     let result = doc.print().unwrap();
 

crates/biome_css_formatter/tests/specs/css/quote_style/normalize_quotes.css

@@ -18,4 +18,8 @@ div {
     width: 0\eestays-unquoted;
     --\eeunquoted: green;
     color: var(--\eeunquoted);
-}
+}
+
+@charset·"UTF-8";
+@charset "iso-8859-15";
+@charset "any-string-is-okay";

crates/biome_css_formatter/tests/specs/css/quote_style/normalize_quotes.css.snap

@@ -26,6 +26,10 @@ div {
     --\eeunquoted: green;
     color: var(--\eeunquoted);
 }
+
+@charset·"UTF-8";
+@charset "iso-8859-15";
+@charset "any-string-is-okay";
 ```
 
 
@@ -65,6 +69,10 @@ div {
 	--\eeunquoted: green;
 	color: var(--\eeunquoted);
 }
+
+@charset· "UTF-8";
+@charset "iso-8859-15";
+@charset "any-string-is-okay";
 ```
 
 ## Output 1
@@ -99,4 +107,8 @@ div {
 	--\eeunquoted: green;
 	color: var(--\eeunquoted);
 }
+
+@charset· "UTF-8";
+@charset "iso-8859-15";
+@charset "any-string-is-okay";
 ```