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

<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/8526)
<!-- Reviewable:end -->

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;
 };

components/servo/Cargo.lock

@@ -1923,6 +1923,7 @@ dependencies = [
 name = "util_tests"
 version = "0.0.1"
 dependencies = [
+ "app_units 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "plugins 0.0.1",

components/util/str.rs

@@ -303,20 +303,39 @@ pub enum LengthOrPercentageOrAuto {
     Length(Au),
 }
 
-/// Parses a length per HTML5 § 2.4.4.4. If unparseable, `Auto` is returned.
+/// TODO: this function can be rewritten to return Result<LengthOrPercentage, _>
+/// Parses a dimension value per HTML5 § 2.4.4.4. If unparseable, `Auto` is
+/// returned.
+/// https://html.spec.whatwg.org/multipage/#rules-for-parsing-dimension-values
 pub fn parse_length(mut value: &str) -> LengthOrPercentageOrAuto {
+    // Steps 1 & 2 are not relevant
+
+    // Step 3
     value = value.trim_left_matches(WHITESPACE);
-    if value.is_empty() {
-        return LengthOrPercentageOrAuto::Auto
-    }
-    if value.starts_with("+") {
-        value = &value[1..]
-    }
-    value = value.trim_left_matches('0');
+
+    // Step 4
     if value.is_empty() {
         return LengthOrPercentageOrAuto::Auto
     }
 
+    // Step 5
+    if value.starts_with("+") {
+        value = &value[1..]
+    }
+
+    // Steps 6 & 7
+    match value.chars().nth(0) {
+        Some('0'...'9') => {},
+        _ => return LengthOrPercentageOrAuto::Auto,
+    }
+
+    // Steps 8 to 13
+    // We trim the string length to the minimum of:
+    // 1. the end of the string
+    // 2. the first occurence of a '%' (U+0025 PERCENT SIGN)
+    // 3. the second occurrence of a '.' (U+002E FULL STOP)
+    // 4. the occurrence of a character that is neither a digit nor '%' nor '.'
+    // Note: Step 10 is directly subsumed by FromStr::from_str
     let mut end_index = value.len();
     let (mut found_full_stop, mut found_percent) = (false, false);
     for (i, ch) in value.chars().enumerate() {
@@ -348,7 +367,7 @@ pub fn parse_length(mut value: &str) -> LengthOrPercentageOrAuto {
     }
 
     match FromStr::from_str(value) {
-        Ok(number) => LengthOrPercentageOrAuto::Length(Au::from_px(number)),
+        Ok(number) => LengthOrPercentageOrAuto::Length(Au::from_f64_px(number)),
         Err(_) => LengthOrPercentageOrAuto::Auto,
     }
 }