Auto merge of #16319 - canaltinova:element, r=upsuper

stylo: Add -moz-element support

Implemented -moz-element for background property.
r=upsuper

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #15443 and [Bug 1341761](https://bugzilla.mozilla.org/show_bug.cgi?id=1341761)

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components/layout/display_list_builder.rs

@@ -657,6 +657,9 @@ impl FragmentDisplayListBuilding for Fragment {
                 Some(computed::Image::ImageRect(_)) => {
                     // TODO: Implement `-moz-image-rect`
                 }
+                Some(computed::Image::Element(_)) => {
+                    // TODO: Implement `-moz-element`
+                }
             }
         }
     }
@@ -1154,6 +1157,9 @@ impl FragmentDisplayListBuilding for Fragment {
             Some(computed::Image::ImageRect(..)) => {
                 // TODO: Handle border-image with `-moz-image-rect`.
             }
+            Some(computed::Image::Element(..)) => {
+                // TODO: Handle border-image with `-moz-element`.
+            }
             Some(computed::Image::Url(ref image_url)) => {
                 if let Some(url) = image_url.url() {
                     let webrender_image = state.layout_context

components/style/gecko/conversions.rs

@@ -11,7 +11,7 @@
 use app_units::Au;
 use gecko::values::{convert_rgba_to_nscolor, GeckoStyleCoordConvertible};
 use gecko_bindings::bindings::{Gecko_CreateGradient, Gecko_SetGradientImageValue, Gecko_SetUrlImageValue};
-use gecko_bindings::bindings::Gecko_InitializeImageCropRect;
+use gecko_bindings::bindings::{Gecko_InitializeImageCropRect, Gecko_SetImageElement};
 use gecko_bindings::structs::{nsStyleCoord_CalcValue, nsStyleImage};
 use gecko_bindings::structs::{nsresult, SheetType};
 use gecko_bindings::sugar::ns_style_coord::{CoordDataValue, CoordDataMut};
@@ -141,6 +141,11 @@ impl nsStyleImage {
                     image_rect.left.to_gecko_style_coord(&mut rect.data_at_mut(3));
                 }
             }
+            Image::Element(ref element) => {
+                unsafe {
+                    Gecko_SetImageElement(self, element.as_ptr());
+                }
+            },
             _ => (),
         }
     }

components/style/gecko_bindings/bindings.rs

@@ -722,6 +722,10 @@ extern "C" {
     pub fn Gecko_SetUrlImageValue(image: *mut nsStyleImage,
                                   uri: ServoBundledURI);
 }
+extern "C" {
+    pub fn Gecko_SetImageElement(image: *mut nsStyleImage,
+                                 atom: *mut nsIAtom);
+}
 extern "C" {
     pub fn Gecko_CopyImageValueFrom(image: *mut nsStyleImage,
                                     other: *const nsStyleImage);

components/style/values/computed/image.rs

@@ -7,7 +7,8 @@
 //!
 //! [image]: https://drafts.csswg.org/css-images/#image-values
 
-use cssparser::Color as CSSColor;
+use Atom;
+use cssparser::{Color as CSSColor, serialize_identifier};
 use std::f32::consts::PI;
 use std::fmt;
 use style_traits::ToCss;
@@ -31,6 +32,9 @@ impl ToComputedValue for specified::Image {
             },
             specified::Image::ImageRect(ref image_rect) => {
                 Image::ImageRect(image_rect.to_computed_value(context))
+            },
+            specified::Image::Element(ref selector) => {
+                Image::Element(selector.clone())
             }
         }
     }
@@ -51,6 +55,9 @@ impl ToComputedValue for specified::Image {
                     ToComputedValue::from_computed_value(image_rect)
                 )
             },
+            Image::Element(ref selector) => {
+                specified::Image::Element(selector.clone())
+            },
         }
     }
 }
@@ -64,6 +71,7 @@ pub enum Image {
     Url(SpecifiedUrl),
     Gradient(Gradient),
     ImageRect(ImageRect),
+    Element(Atom),
 }
 
 impl fmt::Debug for Image {
@@ -80,6 +88,11 @@ impl fmt::Debug for Image {
                 }
             },
             Image::ImageRect(ref image_rect) => write!(f, "{:?}", image_rect),
+            Image::Element(ref selector) => {
+                f.write_str("-moz-element(#")?;
+                serialize_identifier(&*selector.to_string(), f)?;
+                f.write_str(")")
+            },
         }
     }
 }
@@ -90,6 +103,12 @@ impl ToCss for Image {
             Image::Url(ref url) => url.to_css(dest),
             Image::Gradient(ref gradient) => gradient.to_css(dest),
             Image::ImageRect(ref image_rect) => image_rect.to_css(dest),
+            Image::Element(ref selector) => {
+                dest.write_str("-moz-element(#")?;
+                // FIXME: We should get rid of these intermediate strings.
+                serialize_identifier(&*selector.to_string(), dest)?;
+                dest.write_str(")")
+            },
         }
     }
 }

components/style/values/specified/image.rs

@@ -7,7 +7,8 @@
 //!
 //! [image]: https://drafts.csswg.org/css-images/#image-values
 
-use cssparser::Parser;
+use Atom;
+use cssparser::{Parser, Token, serialize_identifier};
 use parser::{Parse, ParserContext};
 #[cfg(feature = "servo")]
 use servo_url::ServoUrl;
@@ -28,6 +29,8 @@ pub enum Image {
     Gradient(Gradient),
     /// A `-moz-image-rect` image
     ImageRect(ImageRect),
+    /// A `-moz-element(# <element-id>)`
+    Element(Atom),
 }
 
 impl ToCss for Image {
@@ -36,6 +39,12 @@ impl ToCss for Image {
             Image::Url(ref url_value) => url_value.to_css(dest),
             Image::Gradient(ref gradient) => gradient.to_css(dest),
             Image::ImageRect(ref image_rect) => image_rect.to_css(dest),
+            Image::Element(ref selector) => {
+                dest.write_str("-moz-element(#")?;
+                // FIXME: We should get rid of these intermediate strings.
+                serialize_identifier(&*selector.to_string(), dest)?;
+                dest.write_str(")")
+            },
         }
     }
 }
@@ -49,8 +58,11 @@ impl Image {
         if let Ok(gradient) = input.try(|input| Gradient::parse_function(context, input)) {
             return Ok(Image::Gradient(gradient));
         }
+        if let Ok(image_rect) = input.try(|input| ImageRect::parse(context, input)) {
+            return Ok(Image::ImageRect(image_rect));
+        }
 
-        Ok(Image::ImageRect(ImageRect::parse(context, input)?))
+        Ok(Image::Element(Image::parse_element(input)?))
     }
 
     /// Creates an already specified image value from an already resolved URL
@@ -59,6 +71,20 @@ impl Image {
     pub fn for_cascade(url: ServoUrl) -> Self {
         Image::Url(SpecifiedUrl::for_cascade(url))
     }
+
+    /// Parses a `-moz-element(# <element-id>)`.
+    fn parse_element(input: &mut Parser) -> Result<Atom, ()> {
+        if input.try(|i| i.expect_function_matching("-moz-element")).is_ok() {
+            input.parse_nested_block(|i| {
+                match i.next()? {
+                    Token::IDHash(id) => Ok(Atom::from(id)),
+                    _ => Err(()),
+                }
+            })
+        } else {
+            Err(())
+        }
+    }
 }
 
 /// Specified values for a CSS gradient.