Parse the aspect-ratio property

Fixes parcel-bundler#494

Author: devongovett

src/lib.rs

@@ -3860,6 +3860,11 @@ mod tests {
         },
       );
     }
+
+    minify_test(".foo { aspect-ratio: auto }", ".foo{aspect-ratio:auto}");
+    minify_test(".foo { aspect-ratio: 2 / 3 }", ".foo{aspect-ratio:2/3}");
+    minify_test(".foo { aspect-ratio: auto 2 / 3 }", ".foo{aspect-ratio:auto 2/3}");
+    minify_test(".foo { aspect-ratio: 2 / 3 auto }", ".foo{aspect-ratio:auto 2/3}");
   }
 
   #[test]

src/properties/mod.rs

@@ -127,7 +127,7 @@ use crate::parser::starts_with_ignore_ascii_case;
 use crate::parser::ParserOptions;
 use crate::prefixes::Feature;
 use crate::printer::{Printer, PrinterOptions};
-use crate::targets::{Targets};
+use crate::targets::Targets;
 use crate::traits::{Parse, ParseWithOptions, Shorthand, ToCss};
 use crate::values::number::{CSSInteger, CSSNumber};
 use crate::values::string::CowArcStr;
@@ -1184,6 +1184,7 @@ define_properties! {
   "max-block-size": MaxBlockSize(MaxSize) [logical_group: MaxSize, category: Logical],
   "max-inline-size": MaxInlineSize(MaxSize) [logical_group: MaxSize, category: Logical],
   "box-sizing": BoxSizing(BoxSizing, VendorPrefix) / WebKit / Moz,
+  "aspect-ratio": AspectRatio(AspectRatio),
 
   "overflow": Overflow(Overflow) shorthand: true,
   "overflow-x": OverflowX(OverflowKeyword),

src/properties/size.rs

@@ -10,6 +10,7 @@ use crate::printer::Printer;
 use crate::properties::{Property, PropertyId};
 use crate::traits::{IsCompatible, Parse, PropertyHandler, ToCss};
 use crate::values::length::LengthPercentage;
+use crate::values::ratio::Ratio;
 use crate::vendor_prefix::VendorPrefix;
 #[cfg(feature = "visitor")]
 use crate::visitor::Visit;
@@ -293,6 +294,57 @@ enum_property! {
   }
 }
 
+/// A value for the [aspect-ratio](https://drafts.csswg.org/css-sizing-4/#aspect-ratio) property.
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(feature = "visitor", derive(Visit))]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "jsonschema", derive(schemars::JsonSchema))]
+pub struct AspectRatio {
+  /// The `auto` keyword.
+  pub auto: bool,
+  /// A preferred aspect ratio for the box, specified as width / height.
+  pub ratio: Option<Ratio>,
+}
+
+impl<'i> Parse<'i> for AspectRatio {
+  fn parse<'t>(input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i, ParserError<'i>>> {
+    let location = input.current_source_location();
+    let mut auto = input.try_parse(|i| i.expect_ident_matching("auto"));
+    let ratio = input.try_parse(Ratio::parse);
+    if auto.is_err() {
+      auto = input.try_parse(|i| i.expect_ident_matching("auto"));
+    }
+    if auto.is_err() && ratio.is_err() {
+      return Err(location.new_custom_error(ParserError::InvalidValue));
+    }
+
+    Ok(AspectRatio {
+      auto: auto.is_ok(),
+      ratio: ratio.ok(),
+    })
+  }
+}
+
+impl ToCss for AspectRatio {
+  fn to_css<W>(&self, dest: &mut Printer<W>) -> Result<(), PrinterError>
+  where
+    W: std::fmt::Write,
+  {
+    if self.auto {
+      dest.write_str("auto")?;
+    }
+
+    if let Some(ratio) = &self.ratio {
+      if self.auto {
+        dest.write_char(' ')?;
+      }
+      ratio.to_css(dest)?;
+    }
+
+    Ok(())
+  }
+}
+
 property_bitflags! {
   #[derive(Default)]
   struct SizeProperty: u16 {