1 files changed, 136 insertions, 0 deletions
diff --git a/servo/components/style/values/specified/source_size_list.rs b/servo/components/style/values/specified/source_size_list.rs
new file mode 100644
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+++ b/servo/components/style/values/specified/source_size_list.rs
@@ -0,0 +1,136 @@
+/* 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/. */
+
+//! https://html.spec.whatwg.org/multipage/#source-size-list
+
+use crate::media_queries::Device;
+use crate::parser::{Parse, ParserContext};
+use crate::queries::{FeatureType, QueryCondition};
+use crate::values::computed::{self, ToComputedValue};
+use crate::values::specified::{Length, NoCalcLength, ViewportPercentageLength};
+use app_units::Au;
+use cssparser::{Delimiter, Parser, Token};
+use selectors::context::QuirksMode;
+use style_traits::ParseError;
+
+/// A value for a `<source-size>`:
+///
+/// https://html.spec.whatwg.org/multipage/#source-size
+#[derive(Debug)]
+pub struct SourceSize {
+    condition: QueryCondition,
+    value: Length,
+}
+
+impl Parse for SourceSize {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let condition = QueryCondition::parse(context, input, FeatureType::Media)?;
+        let value = Length::parse_non_negative(context, input)?;
+        Ok(Self { condition, value })
+    }
+}
+
+/// A value for a `<source-size-list>`:
+///
+/// https://html.spec.whatwg.org/multipage/#source-size-list
+#[derive(Debug)]
+pub struct SourceSizeList {
+    source_sizes: Vec<SourceSize>,
+    value: Option<Length>,
+}
+
+impl SourceSizeList {
+    /// Create an empty `SourceSizeList`, which can be used as a fall-back.
+    pub fn empty() -> Self {
+        Self {
+            source_sizes: vec![],
+            value: None,
+        }
+    }
+
+    /// Evaluate this <source-size-list> to get the final viewport length.
+    pub fn evaluate(&self, device: &Device, quirks_mode: QuirksMode) -> Au {
+        computed::Context::for_media_query_evaluation(device, quirks_mode, |context| {
+            let matching_source_size = self.source_sizes.iter().find(|source_size| {
+                source_size
+                    .condition
+                    .matches(context)
+                    .to_bool(/* unknown = */ false)
+            });
+
+            match matching_source_size {
+                Some(source_size) => source_size.value.to_computed_value(context),
+                None => match self.value {
+                    Some(ref v) => v.to_computed_value(context),
+                    None => Length::NoCalc(NoCalcLength::ViewportPercentage(
+                        ViewportPercentageLength::Vw(100.),
+                    ))
+                    .to_computed_value(context),
+                },
+            }
+        })
+        .into()
+    }
+}
+
+enum SourceSizeOrLength {
+    SourceSize(SourceSize),
+    Length(Length),
+}
+
+impl Parse for SourceSizeOrLength {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        if let Ok(size) = input.try_parse(|input| SourceSize::parse(context, input)) {
+            return Ok(SourceSizeOrLength::SourceSize(size));
+        }
+
+        let length = Length::parse_non_negative(context, input)?;
+        Ok(SourceSizeOrLength::Length(length))
+    }
+}
+
+impl SourceSizeList {
+    /// NOTE(emilio): This doesn't match the grammar in the spec, see:
+    ///
+    /// https://html.spec.whatwg.org/multipage/#parsing-a-sizes-attribute
+    pub fn parse<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>) -> Self {
+        let mut source_sizes = vec![];
+
+        loop {
+            let result = input.parse_until_before(Delimiter::Comma, |input| {
+                SourceSizeOrLength::parse(context, input)
+            });
+
+            match result {
+                Ok(SourceSizeOrLength::Length(value)) => {
+                    return Self {
+                        source_sizes,
+                        value: Some(value),
+                    };
+                },
+                Ok(SourceSizeOrLength::SourceSize(source_size)) => {
+                    source_sizes.push(source_size);
+                },
+                Err(..) => {},
+            }
+
+            match input.next() {
+                Ok(&Token::Comma) => {},
+                Err(..) => break,
+                _ => unreachable!(),
+            }
+        }
+
+        SourceSizeList {
+            source_sizes,
+            value: None,
+        }
+    }
+}