Auto merge of #16960 - servo:derive-all-the-things, r=emilio

Derive HasViewportPercentage 🍷

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components/style_traits/lib.rs

@@ -63,6 +63,8 @@ pub enum CSSPixel {}
 pub mod cursor;
 #[macro_use]
 pub mod values;
+#[macro_use]
 pub mod viewport;
 
 pub use values::{ToCss, OneOrMoreCommaSeparated};
+pub use viewport::HasViewportPercentage;

components/style_traits/viewport.rs

@@ -20,6 +20,48 @@ define_css_keyword_enum!(Orientation:
                          "portrait" => Portrait,
                          "landscape" => Landscape);
 
+/// A trait used to query whether this value has viewport units.
+pub trait HasViewportPercentage {
+    /// Returns true if this value has viewport units.
+    fn has_viewport_percentage(&self) -> bool;
+}
+
+/// A macro used to implement HasViewportPercentage trait
+/// for a given type that may never contain viewport units.
+#[macro_export]
+macro_rules! no_viewport_percentage {
+    ($($name: ident),+) => {
+        $(impl $crate::HasViewportPercentage for $name {
+            #[inline]
+            fn has_viewport_percentage(&self) -> bool {
+                false
+            }
+        })+
+    };
+}
+
+no_viewport_percentage!(bool, f32);
+
+impl<T: HasViewportPercentage> HasViewportPercentage for Box<T> {
+    #[inline]
+    fn has_viewport_percentage(&self) -> bool {
+        (**self).has_viewport_percentage()
+    }
+}
+
+impl<T: HasViewportPercentage> HasViewportPercentage for Option<T> {
+    #[inline]
+    fn has_viewport_percentage(&self) -> bool {
+        self.as_ref().map_or(false, T::has_viewport_percentage)
+    }
+}
+
+impl<T: HasViewportPercentage> HasViewportPercentage for Vec<T> {
+    #[inline]
+    fn has_viewport_percentage(&self) -> bool {
+        self.iter().any(T::has_viewport_percentage)
+    }
+}
 
 /// A set of viewport descriptors:
 ///