feat(css-parser): CSS Parser: parse starting-style at rule #1478 (#1518)

crates/biome_css_formatter/src/css/any/at_rule.rs

@@ -22,6 +22,7 @@ impl FormatRule<AnyCssAtRule> for FormatAnyCssAtRule {
             AnyCssAtRule::CssScopeAtRule(node) => node.format().fmt(f),
             AnyCssAtRule::CssImportAtRule(node) => node.format().fmt(f),
             AnyCssAtRule::CssNamespaceAtRule(node) => node.format().fmt(f),
+            AnyCssAtRule::CssStartingStyleAtRule(node) => node.format().fmt(f),
             AnyCssAtRule::CssBogusAtRule(node) => node.format().fmt(f),
         }
     }

crates/biome_css_formatter/src/css/any/mod.rs

@@ -56,6 +56,7 @@ pub(crate) mod rule_list_block;
 pub(crate) mod scope_range;
 pub(crate) mod selector;
 pub(crate) mod simple_selector;
+pub(crate) mod starting_style_block;
 pub(crate) mod sub_selector;
 pub(crate) mod supports_and_combinable_condition;
 pub(crate) mod supports_condition;

crates/biome_css_formatter/src/css/any/starting_style_block.rs

@@ -0,0 +1,16 @@
+//! This is a generated file. Don't modify it by hand! Run 'cargo codegen formatter' to re-generate the file.
+
+use crate::prelude::*;
+use biome_css_syntax::AnyCssStartingStyleBlock;
+#[derive(Debug, Clone, Default)]
+pub(crate) struct FormatAnyCssStartingStyleBlock;
+impl FormatRule<AnyCssStartingStyleBlock> for FormatAnyCssStartingStyleBlock {
+    type Context = CssFormatContext;
+    fn fmt(&self, node: &AnyCssStartingStyleBlock, f: &mut CssFormatter) -> FormatResult<()> {
+        match node {
+            AnyCssStartingStyleBlock::CssRuleListBlock(node) => node.format().fmt(f),
+            AnyCssStartingStyleBlock::CssDeclarationListBlock(node) => node.format().fmt(f),
+            AnyCssStartingStyleBlock::CssBogusBlock(node) => node.format().fmt(f),
+        }
+    }
+}

crates/biome_css_formatter/src/css/statements/mod.rs

@@ -15,4 +15,5 @@ pub(crate) mod media_at_rule;
 pub(crate) mod namespace_at_rule;
 pub(crate) mod page_at_rule;
 pub(crate) mod scope_at_rule;
+pub(crate) mod starting_style_at_rule;
 pub(crate) mod supports_at_rule;

crates/biome_css_formatter/src/css/statements/starting_style_at_rule.rs

@@ -0,0 +1,10 @@
+use crate::prelude::*;
+use biome_css_syntax::CssStartingStyleAtRule;
+use biome_rowan::AstNode;
+#[derive(Debug, Clone, Default)]
+pub(crate) struct FormatCssStartingStyleAtRule;
+impl FormatNodeRule<CssStartingStyleAtRule> for FormatCssStartingStyleAtRule {
+    fn fmt_fields(&self, node: &CssStartingStyleAtRule, f: &mut CssFormatter) -> FormatResult<()> {
+        format_verbatim_node(node.syntax()).fmt(f)
+    }
+}

crates/biome_css_formatter/src/generated.rs

@@ -2680,6 +2680,46 @@ impl IntoFormat<CssFormatContext> for biome_css_syntax::CssNamespaceAtRule {
         )
     }
 }
+impl FormatRule<biome_css_syntax::CssStartingStyleAtRule>
+    for crate::css::statements::starting_style_at_rule::FormatCssStartingStyleAtRule
+{
+    type Context = CssFormatContext;
+    #[inline(always)]
+    fn fmt(
+        &self,
+        node: &biome_css_syntax::CssStartingStyleAtRule,
+        f: &mut CssFormatter,
+    ) -> FormatResult<()> {
+        FormatNodeRule::<biome_css_syntax::CssStartingStyleAtRule>::fmt(self, node, f)
+    }
+}
+impl AsFormat<CssFormatContext> for biome_css_syntax::CssStartingStyleAtRule {
+    type Format<'a> = FormatRefWithRule<
+        'a,
+        biome_css_syntax::CssStartingStyleAtRule,
+        crate::css::statements::starting_style_at_rule::FormatCssStartingStyleAtRule,
+    >;
+    fn format(&self) -> Self::Format<'_> {
+        #![allow(clippy::default_constructed_unit_structs)]
+        FormatRefWithRule::new(
+            self,
+            crate::css::statements::starting_style_at_rule::FormatCssStartingStyleAtRule::default(),
+        )
+    }
+}
+impl IntoFormat<CssFormatContext> for biome_css_syntax::CssStartingStyleAtRule {
+    type Format = FormatOwnedWithRule<
+        biome_css_syntax::CssStartingStyleAtRule,
+        crate::css::statements::starting_style_at_rule::FormatCssStartingStyleAtRule,
+    >;
+    fn into_format(self) -> Self::Format {
+        #![allow(clippy::default_constructed_unit_structs)]
+        FormatOwnedWithRule::new(
+            self,
+            crate::css::statements::starting_style_at_rule::FormatCssStartingStyleAtRule::default(),
+        )
+    }
+}
 impl FormatRule<biome_css_syntax::CssContainerNotQuery>
     for crate::css::auxiliary::container_not_query::FormatCssContainerNotQuery
 {
@@ -7621,6 +7661,33 @@ impl IntoFormat<CssFormatContext> for biome_css_syntax::AnyCssNamespaceUrl {
         )
     }
 }
+impl AsFormat<CssFormatContext> for biome_css_syntax::AnyCssStartingStyleBlock {
+    type Format<'a> = FormatRefWithRule<
+        'a,
+        biome_css_syntax::AnyCssStartingStyleBlock,
+        crate::css::any::starting_style_block::FormatAnyCssStartingStyleBlock,
+    >;
+    fn format(&self) -> Self::Format<'_> {
+        #![allow(clippy::default_constructed_unit_structs)]
+        FormatRefWithRule::new(
+            self,
+            crate::css::any::starting_style_block::FormatAnyCssStartingStyleBlock::default(),
+        )
+    }
+}
+impl IntoFormat<CssFormatContext> for biome_css_syntax::AnyCssStartingStyleBlock {
+    type Format = FormatOwnedWithRule<
+        biome_css_syntax::AnyCssStartingStyleBlock,
+        crate::css::any::starting_style_block::FormatAnyCssStartingStyleBlock,
+    >;
+    fn into_format(self) -> Self::Format {
+        #![allow(clippy::default_constructed_unit_structs)]
+        FormatOwnedWithRule::new(
+            self,
+            crate::css::any::starting_style_block::FormatAnyCssStartingStyleBlock::default(),
+        )
+    }
+}
 impl AsFormat<CssFormatContext> for biome_css_syntax::AnyCssUrlValue {
     type Format<'a> = FormatRefWithRule<
         'a,

crates/biome_css_parser/src/lexer/mod.rs

@@ -997,6 +997,7 @@ impl<'src> CssLexer<'src> {
             b"scope" => SCOPE_KW,
             b"import" => IMPORT_KW,
             b"namespace" => NAMESPACE_KW,
+            b"starting-style" => STARTING_STYLE_KW,
             _ => IDENT,
         }
     }

crates/biome_css_parser/src/state.rs

@@ -11,12 +11,22 @@ pub(crate) struct CssParserState {
     /// The challenge is, that it isn't possible to tell which of the two kinds it is until the parser
     /// processed all of `(a, b)`.
     pub(crate) speculative_parsing: bool,
+
+    /// Indicates whether the parser is currently dealing with a nesting block in the CSS document.
+    ///
+    /// This field is essential for understanding the current context of the parser. When set to `true`,
+    /// it indicates that the parser is inside a nested or inner element, such as rules within media queries
+    /// or other nested structures. Conversely, when set to `false`, it implies that the parser is at the root level,
+    /// handling top-level `@rules` or style declarations directly under the stylesheet.
+    /// This distinction is critical for correctly interpreting and parsing different sections of a CSS document.
+    pub(crate) is_nesting_block: bool,
 }
 
 impl CssParserState {
     pub fn new() -> Self {
         Self {
             speculative_parsing: false,
+            is_nesting_block: false,
         }
     }
 }

crates/biome_css_parser/src/syntax/at_rule/keyframes.rs

@@ -3,7 +3,7 @@ use crate::parser::CssParser;
 use crate::syntax::at_rule::parse_error::{
     expected_keyframes_item, expected_keyframes_item_selector,
 };
-use crate::syntax::blocks::parse_declaration_list_block;
+use crate::syntax::blocks::{parse_block_body, parse_declaration_list_block};
 use crate::syntax::css_dimension::{is_at_percentage_dimension, parse_percentage_dimension};
 use crate::syntax::parse_error::{expected_block, expected_non_css_wide_keyword_identifier};
 use crate::syntax::{
@@ -74,10 +74,9 @@ fn parse_keyframes_block(p: &mut CssParser) -> ParsedSyntax {
         return Absent;
     }
 
-    let m = p.start();
-    p.bump(T!['{']);
-    KeyframesItemList.parse_list(p);
-    p.expect(T!['}']);
+    let m = parse_block_body(p, |p| {
+        KeyframesItemList.parse_list(p);
+    });
 
     Present(m.complete(p, CSS_KEYFRAMES_BLOCK))
 }
@@ -141,7 +140,7 @@ impl ParseRecovery for KeyframesItemBlockParseRecovery {
         //          color: blue;
         //      }
         //   }
-        p.at_ts(token_set!(T!['}'])) || is_at_keyframes_item_selector(p)
+        p.at(T!['}']) || is_at_keyframes_item_selector(p)
     }
 }
 

crates/biome_css_parser/src/syntax/at_rule/mod.rs

@@ -13,6 +13,7 @@ mod namespace;
 mod page;
 mod parse_error;
 mod scope;
+mod starting_style;
 mod supports;
 
 use crate::parser::CssParser;
@@ -35,6 +36,9 @@ use crate::syntax::at_rule::media::{is_at_media_at_rule, parse_media_at_rule};
 use crate::syntax::at_rule::namespace::{is_at_namespace_at_rule, parse_namespace_at_rule};
 use crate::syntax::at_rule::page::{is_at_page_at_rule, parse_page_at_rule};
 use crate::syntax::at_rule::scope::{is_at_scope_at_rule, parse_scope_at_rule};
+use crate::syntax::at_rule::starting_style::{
+    is_at_starting_style_at_rule, parse_starting_style_at_rule,
+};
 use crate::syntax::at_rule::supports::{is_at_supports_at_rule, parse_supports_at_rule};
 use crate::syntax::parse_error::expected_any_at_rule;
 use biome_css_syntax::CssSyntaxKind::*;
@@ -99,6 +103,8 @@ pub(crate) fn parse_any_at_rule(p: &mut CssParser) -> ParsedSyntax {
         parse_import_at_rule(p)
     } else if is_at_namespace_at_rule(p) {
         parse_namespace_at_rule(p)
+    } else if is_at_starting_style_at_rule(p) {
+        parse_starting_style_at_rule(p)
     } else {
         Absent
     }

crates/biome_css_parser/src/syntax/at_rule/page.rs

@@ -4,7 +4,7 @@ use crate::syntax::at_rule::parse_error::{
     expected_any_page_at_rule_item, expected_page_selector, expected_page_selector_pseudo,
 };
 use crate::syntax::at_rule::{is_at_at_rule, parse_at_rule};
-use crate::syntax::blocks::parse_or_recover_declaration_or_rule_list_block;
+use crate::syntax::blocks::{parse_block_body, parse_or_recover_declaration_or_rule_list_block};
 use crate::syntax::parse_error::expected_block;
 use crate::syntax::{
     is_at_identifier, parse_custom_identifier_with_keywords, parse_declaration_with_semicolon,
@@ -176,11 +176,10 @@ pub(crate) fn parse_page_block(p: &mut CssParser) -> ParsedSyntax {
     if !p.at(T!['{']) {
         return Absent;
     }
-    let m = p.start();
 
-    p.expect(T!['{']);
-    PageAtRuleItemList.parse_list(p);
-    p.expect(T!['}']);
+    let m = parse_block_body(p, |p| {
+        PageAtRuleItemList.parse_list(p);
+    });
 
     Present(m.complete(p, CSS_PAGE_AT_RULE_BLOCK))
 }

crates/biome_css_parser/src/syntax/at_rule/starting_style.rs

@@ -0,0 +1,65 @@
+use crate::parser::CssParser;
+use crate::syntax::blocks::{
+    parse_or_recover_declaration_list_block, parse_or_recover_rule_list_block,
+};
+use biome_css_syntax::CssSyntaxKind::*;
+use biome_css_syntax::T;
+use biome_parser::parsed_syntax::ParsedSyntax::Present;
+use biome_parser::prelude::ParsedSyntax::Absent;
+use biome_parser::prelude::*;
+
+/// Checks if the current token in the parser is a `@starting-style` at-rule.
+///
+/// This function verifies if the current token matches the `@starting-style` rule,
+/// which is a custom at-rule used for specific parsing scenarios.
+#[inline]
+pub(crate) fn is_at_starting_style_at_rule(p: &mut CssParser) -> bool {
+    p.at(T![starting_style])
+}
+
+/// Parses a `@starting-style` at-rule in a CSS stylesheet.
+///
+/// This function handles the parsing of a `@starting-style` at-rule, which is defined in the
+/// CSS Transitions Level 2 specification. It starts by confirming the presence of such a rule and then
+/// processes the content depending on whether the parser is currently inside a nesting block or at the root level.
+/// It employs different parsing strategies for declarations or rules based on the parser state `is_nesting_block`.
+///
+/// Specification: [CSS Transitions Level 2 - @starting-style](https://drafts.csswg.org/css-transitions-2/#at-ruledef-starting-style)
+/// # Examples
+/// Basic usage in a CSS stylesheet:
+///
+/// ```css
+/// // At the root level of a stylesheet
+/// @starting-style {
+///     /* rulesets */
+/// }
+///
+/// // Inside a selector
+/// selector {
+///   @starting-style {
+///     /* declarations */
+///   }
+/// }
+/// ```
+#[inline]
+pub(crate) fn parse_starting_style_at_rule(p: &mut CssParser) -> ParsedSyntax {
+    if !is_at_starting_style_at_rule(p) {
+        return Absent;
+    }
+
+    let m = p.start();
+
+    p.bump(T![starting_style]);
+
+    let block = if p.state().is_nesting_block {
+        parse_or_recover_declaration_list_block(p)
+    } else {
+        parse_or_recover_rule_list_block(p)
+    };
+
+    if block.is_err() {
+        return Present(m.complete(p, CSS_BOGUS_AT_RULE));
+    }
+
+    Present(m.complete(p, CSS_STARTING_STYLE_AT_RULE))
+}