Auto merge of #8526 - frewsxcv:parse-length, r=eefriedman

Fix parse_length 0 values, implement <hr> 'width'

Follow-up to https://github.com/servo/servo/issues/8424

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components/script/dom/element.rs

@@ -390,6 +390,9 @@ impl LayoutElementHelpers for LayoutJS<Element> {
             this.get_width()
         } else if let Some(this) = self.downcast::<HTMLTableCellElement>() {
             this.get_width()
+        } else if let Some(this) = self.downcast::<HTMLHRElement>() {
+            // https://html.spec.whatwg.org/multipage/#the-hr-element-2:attr-hr-width
+            this.get_width()
         } else {
             LengthOrPercentageOrAuto::Auto
         };

components/script/dom/htmlhrelement.rs

@@ -13,7 +13,7 @@ use dom::htmlelement::HTMLElement;
 use dom::node::Node;
 use dom::virtualmethods::VirtualMethods;
 use string_cache::Atom;
-use util::str::DOMString;
+use util::str::{DOMString, LengthOrPercentageOrAuto};
 
 #[dom_struct]
 pub struct HTMLHRElement {
@@ -42,10 +42,17 @@ impl HTMLHRElementMethods for HTMLHRElement {
 
     // https://html.spec.whatwg.org/multipage/#dom-hr-color
     make_legacy_color_setter!(SetColor, "color");
+
+    // https://html.spec.whatwg.org/multipage/#dom-hr-width
+    make_getter!(Width);
+
+    // https://html.spec.whatwg.org/multipage/#dom-hr-width
+    make_dimension_setter!(SetWidth, "width");
 }
 
 pub trait HTMLHRLayoutHelpers {
     fn get_color(&self) -> Option<RGBA>;
+    fn get_width(&self) -> LengthOrPercentageOrAuto;
 }
 
 impl HTMLHRLayoutHelpers for LayoutJS<HTMLHRElement> {
@@ -58,6 +65,17 @@ impl HTMLHRLayoutHelpers for LayoutJS<HTMLHRElement> {
                 .cloned()
         }
     }
+
+    #[allow(unsafe_code)]
+    fn get_width(&self) -> LengthOrPercentageOrAuto {
+        unsafe {
+            (&*self.upcast::<Element>().unsafe_get())
+                .get_attr_for_layout(&ns!(""), &atom!("width"))
+                .map(AttrValue::as_dimension)
+                .cloned()
+                .unwrap_or(LengthOrPercentageOrAuto::Auto)
+        }
+    }
 }
 
 
@@ -69,6 +87,7 @@ impl VirtualMethods for HTMLHRElement {
     fn parse_plain_attribute(&self, name: &Atom, value: DOMString) -> AttrValue {
         match name {
             &atom!("color") => AttrValue::from_legacy_color(value),
+            &atom!("width") => AttrValue::from_dimension(value),
             _ => self.super_type().unwrap().parse_plain_attribute(name, value),
         }
     }

components/script/dom/webidls/HTMLHRElement.webidl

@@ -14,5 +14,5 @@ partial interface HTMLHRElement {
   attribute DOMString color;
   //         attribute boolean noShade;
   //         attribute DOMString size;
-  //         attribute DOMString width;
+  attribute DOMString width;
 };