Bug 1833538 - [css-properties-values-api] Parsing and serialization for @property syntax descriptor r=emilio

Based off of @emilio's syntax parser at
<https://github.com/emilio/css-typed-om-syntax>.

Co-authored-by: Emilio Cobos Álvarez <emilio@crisal.io>

Differential Revision: https://phabricator.services.mozilla.com/D178268

servo/components/style/lib.rs

@@ -109,6 +109,7 @@ pub mod media_queries;
 pub mod parallel;
 pub mod parser;
 pub mod piecewise_linear;
+pub mod properties_and_values;
 #[macro_use]
 pub mod queries;
 pub mod rule_cache;

servo/components/style/properties_and_values/mod.rs

@@ -0,0 +1,9 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Properties and Values
+//!
+//! https://drafts.css-houdini.org/css-properties-values-api-1/
+
+pub mod syntax;

servo/components/style/properties_and_values/syntax/ascii.rs

@@ -0,0 +1,60 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+/// Trims ASCII whitespace characters from a slice, and returns the trimmed input.
+pub fn trim_ascii_whitespace(input: &str) -> &str {
+    if input.is_empty() {
+        return input;
+    }
+
+    let mut start = 0;
+    {
+        let mut iter = input.as_bytes().iter();
+        loop {
+            let byte = match iter.next() {
+                Some(b) => b,
+                None => return "",
+            };
+
+            if !byte.is_ascii_whitespace() {
+                break;
+            }
+            start += 1;
+        }
+    }
+
+    let mut end = input.len();
+    assert!(start < end);
+    {
+        let mut iter = input.as_bytes()[start..].iter().rev();
+        loop {
+            let byte = match iter.next() {
+                Some(b) => b,
+                None => {
+                    debug_assert!(false, "We should have caught this in the loop above!");
+                    return "";
+                },
+            };
+
+            if !byte.is_ascii_whitespace() {
+                break;
+            }
+            end -= 1;
+        }
+    }
+
+    &input[start..end]
+}
+
+#[test]
+fn trim_ascii_whitespace_test() {
+    fn test(i: &str, o: &str) {
+        assert_eq!(trim_ascii_whitespace(i), o)
+    }
+
+    test("", "");
+    test(" ", "");
+    test(" a b c ", "a b c");
+    test(" \t \t \ta b c \t \t \t \t", "a b c");
+}

servo/components/style/properties_and_values/syntax/data_type.rs

@@ -0,0 +1,91 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use super::{Component, ComponentName, Multiplier};
+
+/// <https://drafts.css-houdini.org/css-properties-values-api-1/#supported-names>
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq)]
+pub enum DataType {
+    /// Any valid `<length>` value
+    Length,
+    /// `<number>` values
+    Number,
+    /// Any valid <percentage> value
+    Percentage,
+    /// Any valid `<length>` or `<percentage>` value, any valid `<calc()>` expression combining
+    /// `<length>` and `<percentage>` components.
+    LengthPercentage,
+    /// Any valid `<color>` value
+    Color,
+    /// Any valid `<image>` value
+    Image,
+    /// Any valid `<url>` value
+    Url,
+    /// Any valid `<integer>` value
+    Integer,
+    /// Any valid `<angle>` value
+    Angle,
+    /// Any valid `<time>` value
+    Time,
+    /// Any valid `<resolution>` value
+    Resolution,
+    /// Any valid `<transform-function>` value
+    TransformFunction,
+    /// A list of valid `<transform-function>` values. Note that "<transform-list>" is a pre-multiplied
+    /// data type name equivalent to "<transform-function>+"
+    TransformList,
+    /// Any valid `<custom-ident>` value
+    CustomIdent,
+}
+
+impl DataType {
+    pub fn unpremultiply(&self) -> Option<Component> {
+        match *self {
+            DataType::TransformList => Some(Component {
+                name: ComponentName::DataType(DataType::TransformFunction),
+                multiplier: Some(Multiplier::Space),
+            }),
+            _ => None,
+        }
+    }
+
+    pub fn from_str(ty: &str) -> Option<Self> {
+        Some(match ty.as_bytes() {
+            b"length" => DataType::Length,
+            b"number" => DataType::Number,
+            b"percentage" => DataType::Percentage,
+            b"length-percentage" => DataType::LengthPercentage,
+            b"color" => DataType::Color,
+            b"image" => DataType::Image,
+            b"url" => DataType::Url,
+            b"integer" => DataType::Integer,
+            b"angle" => DataType::Angle,
+            b"time" => DataType::Time,
+            b"resolution" => DataType::Resolution,
+            b"transform-function" => DataType::TransformFunction,
+            b"custom-ident" => DataType::CustomIdent,
+            b"transform-list" => DataType::TransformList,
+            _ => return None,
+        })
+    }
+
+    pub fn to_str(&self) -> &str {
+        match self {
+            DataType::Length => "length",
+            DataType::Number => "number",
+            DataType::Percentage => "percentage",
+            DataType::LengthPercentage => "length-percentage",
+            DataType::Color => "color",
+            DataType::Image => "image",
+            DataType::Url => "url",
+            DataType::Integer => "integer",
+            DataType::Angle => "angle",
+            DataType::Time => "time",
+            DataType::Resolution => "resolution",
+            DataType::TransformFunction => "transform-function",
+            DataType::CustomIdent => "custom-ident",
+            DataType::TransformList => "transform-list",
+        }
+    }
+}

servo/components/style/properties_and_values/syntax/mod.rs

@@ -0,0 +1,328 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Used for parsing and serializing the [`@property`] syntax string.
+//!
+//! <https://drafts.css-houdini.org/css-properties-values-api-1/#parsing-syntax>
+
+use std::fmt::{self, Debug};
+use std::{borrow::Cow, fmt::Write};
+
+use crate::parser::{Parse, ParserContext};
+use crate::values::CustomIdent;
+use cssparser::{Parser as CSSParser, ParserInput as CSSParserInput};
+use style_traits::{
+    CssWriter, ParseError as StyleParseError, PropertySyntaxParseError as ParseError,
+    StyleParseErrorKind, ToCss,
+};
+
+use self::data_type::DataType;
+
+mod ascii;
+mod data_type;
+
+/// <https://drafts.css-houdini.org/css-properties-values-api-1/#parsing-syntax>
+#[derive(Debug, Clone, MallocSizeOf)]
+pub struct Descriptor {
+    components: Box<[Component]>,
+    css: String,
+}
+
+impl Descriptor {
+    /// Returns the universal syntax definition with the given CSS representation.
+    fn universal(css: &str) -> Self {
+        Self {
+            components: Default::default(),
+            css: String::from(css),
+        }
+    }
+
+    /// Returns the specified syntax string.
+    pub fn as_str(&self) -> &str {
+        &self.css
+    }
+}
+
+impl PartialEq for Descriptor {
+    fn eq(&self, other: &Self) -> bool {
+        self.components == other.components
+    }
+}
+
+impl Parse for Descriptor {
+    /// Parse a syntax descriptor.
+    fn parse<'i, 't>(
+        _context: &ParserContext,
+        parser: &mut CSSParser<'i, 't>,
+    ) -> Result<Self, StyleParseError<'i>> {
+        // 1. Strip leading and trailing ASCII whitespace from string.
+        let input = parser.expect_string()?;
+        match parse_descriptor(input) {
+            Ok(syntax) => Ok(syntax),
+            Err(err) => Err(parser.new_custom_error(StyleParseErrorKind::PropertySyntaxField(err))),
+        }
+    }
+}
+
+impl ToCss for Descriptor {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        self.css.to_css(dest)
+    }
+}
+
+/// <https://drafts.css-houdini.org/css-properties-values-api-1/#multipliers>
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq)]
+pub enum Multiplier {
+    /// Indicates a space-separated list.
+    Space,
+    /// Indicates a comma-separated list.
+    Comma,
+}
+
+/// <https://drafts.css-houdini.org/css-properties-values-api-1/#syntax-component>
+#[derive(Clone, Debug, MallocSizeOf, PartialEq)]
+pub struct Component {
+    name: ComponentName,
+    multiplier: Option<Multiplier>,
+}
+
+impl Component {
+    /// Returns the component's name.
+    #[inline]
+    pub fn name(&self) -> &ComponentName {
+        &self.name
+    }
+
+    /// Returns the component's multiplier, if one exists.
+    #[inline]
+    pub fn multiplier(&self) -> Option<Multiplier> {
+        self.multiplier
+    }
+
+    /// If the component is premultiplied, return the un-premultiplied component.
+    #[inline]
+    pub fn unpremultiplied(&self) -> Cow<Self> {
+        match self.name.unpremultiply() {
+            Some(component) => {
+                debug_assert!(
+                    self.multiplier.is_none(),
+                    "Shouldn't have parsed a multiplier for a pre-multiplied data type name",
+                );
+                Cow::Owned(component)
+            },
+            None => Cow::Borrowed(self),
+        }
+    }
+}
+
+/// <https://drafts.css-houdini.org/css-properties-values-api-1/#syntax-component-name>
+#[derive(Clone, Debug, MallocSizeOf, PartialEq)]
+pub enum ComponentName {
+    /// <https://drafts.css-houdini.org/css-properties-values-api-1/#data-type-name>
+    DataType(DataType),
+    /// <https://drafts.csswg.org/css-values-4/#custom-idents>
+    Ident(CustomIdent),
+}
+
+impl ComponentName {
+    fn unpremultiply(&self) -> Option<Component> {
+        match *self {
+            ComponentName::DataType(ref t) => t.unpremultiply(),
+            ComponentName::Ident(..) => None,
+        }
+    }
+
+    /// <https://drafts.css-houdini.org/css-properties-values-api-1/#pre-multiplied-data-type-name>
+    fn is_pre_multiplied(&self) -> bool {
+        self.unpremultiply().is_some()
+    }
+}
+
+/// Parse a syntax descriptor.
+#[inline]
+fn parse_descriptor(css: &str) -> Result<Descriptor, ParseError> {
+    // 1. Strip leading and trailing ASCII whitespace from string.
+    let input = ascii::trim_ascii_whitespace(css);
+
+    // 2. If string's length is 0, return failure.
+    if input.is_empty() {
+        return Err(ParseError::EmptyInput);
+    }
+
+    // 3. If string's length is 1, and the only code point in string is U+002A
+    //    ASTERISK (*), return the universal syntax descriptor.
+    if input.len() == 1 && input.as_bytes()[0] == b'*' {
+        return Ok(Descriptor::universal(css));
+    }
+
+    // 4. Let stream be an input stream created from the code points of string,
+    //    preprocessed as specified in [css-syntax-3]. Let descriptor be an
+    //    initially empty list of syntax components.
+    //
+    // NOTE(emilio): Instead of preprocessing we cheat and treat new-lines and
+    // nulls in the parser specially.
+    let mut components = vec![];
+    {
+        let mut parser = Parser::new(input, &mut components);
+        // 5. Repeatedly consume the next input code point from stream.
+        parser.parse()?;
+    }
+    Ok(Descriptor {
+        components: components.into_boxed_slice(),
+        css: String::from(css),
+    })
+}
+
+struct Parser<'a> {
+    input: &'a str,
+    position: usize,
+    output: &'a mut Vec<Component>,
+}
+
+/// <https://drafts.csswg.org/css-syntax-3/#whitespace>
+fn is_whitespace(byte: u8) -> bool {
+    match byte {
+        b'\t' | b'\n' | b'\r' | b' ' => true,
+        _ => false,
+    }
+}
+
+/// <https://drafts.csswg.org/css-syntax-3/#letter>
+fn is_letter(byte: u8) -> bool {
+    match byte {
+        b'A'..=b'Z' | b'a'..=b'z' => true,
+        _ => false,
+    }
+}
+
+/// <https://drafts.csswg.org/css-syntax-3/#non-ascii-code-point>
+fn is_non_ascii(byte: u8) -> bool {
+    byte >= 0x80
+}
+
+/// <https://drafts.csswg.org/css-syntax-3/#name-start-code-point>
+fn is_name_start(byte: u8) -> bool {
+    is_letter(byte) || is_non_ascii(byte) || byte == b'_'
+}
+
+impl<'a> Parser<'a> {
+    fn new(input: &'a str, output: &'a mut Vec<Component>) -> Self {
+        Self {
+            input,
+            position: 0,
+            output,
+        }
+    }
+
+    fn peek(&self) -> Option<u8> {
+        self.input.as_bytes().get(self.position).cloned()
+    }
+
+    fn parse(&mut self) -> Result<(), ParseError> {
+        // 5. Repeatedly consume the next input code point from stream:
+        loop {
+            let component = self.parse_component()?;
+            self.output.push(component);
+            self.skip_whitespace();
+
+            let byte = match self.peek() {
+                None => return Ok(()),
+                Some(b) => b,
+            };
+
+            if byte != b'|' {
+                return Err(ParseError::ExpectedPipeBetweenComponents);
+            }
+
+            self.position += 1;
+        }
+    }
+
+    fn skip_whitespace(&mut self) {
+        loop {
+            match self.peek() {
+                Some(c) if is_whitespace(c) => self.position += 1,
+                _ => return,
+            }
+        }
+    }
+
+    /// <https://drafts.css-houdini.org/css-properties-values-api-1/#consume-data-type-name>
+    fn parse_data_type_name(&mut self) -> Result<DataType, ParseError> {
+        let start = self.position;
+        loop {
+            let byte = match self.peek() {
+                Some(b) => b,
+                None => return Err(ParseError::UnclosedDataTypeName),
+            };
+            if byte != b'>' {
+                self.position += 1;
+                continue;
+            }
+            let ty = match DataType::from_str(&self.input[start..self.position]) {
+                Some(ty) => ty,
+                None => return Err(ParseError::UnknownDataTypeName),
+            };
+            self.position += 1;
+            return Ok(ty);
+        }
+    }
+
+    fn parse_name(&mut self) -> Result<ComponentName, ParseError> {
+        let b = match self.peek() {
+            Some(b) => b,
+            None => return Err(ParseError::UnexpectedEOF),
+        };
+
+        if b == b'<' {
+            self.position += 1;
+            return Ok(ComponentName::DataType(self.parse_data_type_name()?));
+        }
+
+        if b != b'\\' && !is_name_start(b) {
+            return Err(ParseError::InvalidNameStart);
+        }
+
+        let input = &self.input[self.position..];
+        let mut input = CSSParserInput::new(input);
+        let mut input = CSSParser::new(&mut input);
+        let location = input.current_source_location();
+        let name = input
+            .expect_ident()
+            .ok()
+            .and_then(|name| CustomIdent::from_ident(location, name, &[]).ok());
+        let name = match name {
+            Some(name) => name,
+            None => return Err(ParseError::InvalidName),
+        };
+        self.position += input.position().byte_index();
+        return Ok(ComponentName::Ident(name));
+    }
+
+    fn parse_multiplier(&mut self) -> Option<Multiplier> {
+        let multiplier = match self.peek()? {
+            b'+' => Multiplier::Space,
+            b'#' => Multiplier::Comma,
+            _ => return None,
+        };
+        self.position += 1;
+        Some(multiplier)
+    }
+
+    /// <https://drafts.css-houdini.org/css-properties-values-api-1/#consume-a-syntax-component>
+    fn parse_component(&mut self) -> Result<Component, ParseError> {
+        // Consume as much whitespace as possible from stream.
+        self.skip_whitespace();
+        let name = self.parse_name()?;
+        let multiplier = if name.is_pre_multiplied() {
+            None
+        } else {
+            self.parse_multiplier()
+        };
+        Ok(Component { name, multiplier })
+    }
+}

servo/components/style_traits/lib.rs

@@ -133,6 +133,8 @@ pub enum StyleParseErrorKind<'i> {
     RangedExpressionWithNoValue,
     /// A function was encountered that was not expected.
     UnexpectedFunction(CowRcStr<'i>),
+    /// Error encountered parsing a @property's `syntax` descriptor
+    PropertySyntaxField(PropertySyntaxParseError),
     /// @namespace must be before any rule but @charset and @import
     UnexpectedNamespaceRule,
     /// @import must be before any rule but @charset
@@ -214,6 +216,31 @@ impl<'i> StyleParseErrorKind<'i> {
     }
 }
 
+/// Errors that can be encountered while parsing the @property rule's syntax descriptor.
+#[derive(Clone, Debug, PartialEq)]
+pub enum PropertySyntaxParseError {
+    /// The string's length was 0.
+    EmptyInput,
+    /// A non-whitespace, non-pipe character was fount after parsing a component.
+    ExpectedPipeBetweenComponents,
+    /// The start of an identifier was expected but not found.
+    ///
+    /// <https://drafts.csswg.org/css-syntax-3/#name-start-code-point>
+    InvalidNameStart,
+    /// The name is not a valid `<ident>`.
+    InvalidName,
+    /// The data type name was not closed.
+    ///
+    /// <https://drafts.css-houdini.org/css-properties-values-api-1/#consume-data-type-name>
+    UnclosedDataTypeName,
+    /// The next byte was expected while parsing, but EOF was found instead.
+    UnexpectedEOF,
+    /// The data type is not a supported syntax component name.
+    ///
+    /// <https://drafts.css-houdini.org/css-properties-values-api-1/#supported-names>
+    UnknownDataTypeName,
+}
+
 bitflags! {
     /// The mode to use when parsing values.
     pub struct ParsingMode: u8 {