gfx: Make display lists serializable using serde.

This commit introduces the `serde` dependency, which we will use to
serialize messages going between processes in multiprocess Servo.

This also adds a new debugging flag, `-Z print-display-list-json`,
allowing the output of display list serialization to be visualized.
This will be useful for our experiments with alternate rasterizers.

components/util/cursor.rs

@@ -9,7 +9,7 @@ use std::ascii::AsciiExt;
 
 macro_rules! define_cursor {
     ($( $css: expr => $variant: ident = $value: expr, )+) => {
-        #[derive(Clone, Copy, PartialEq, Eq, Debug)]
+        #[derive(Clone, Copy, PartialEq, Eq, Debug, Deserialize, Serialize)]
         #[repr(u8)]
         pub enum Cursor {
             $( $variant = $value ),+

components/util/linked_list.rs

@@ -4,8 +4,81 @@
 
 //! Utility functions for doubly-linked lists.
 
+use mem::HeapSizeOf;
+
+use serde::de::{Error, SeqVisitor, Visitor};
+use serde::ser::impls::SeqIteratorVisitor;
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use std::collections::LinkedList;
+use std::marker::PhantomData;
 use std::mem;
+use std::ops::{Deref, DerefMut};
+
+pub struct SerializableLinkedList<T>(LinkedList<T>);
+
+impl<T> SerializableLinkedList<T> {
+    pub fn new(linked_list: LinkedList<T>) -> SerializableLinkedList<T> {
+        SerializableLinkedList(linked_list)
+    }
+}
+
+impl<T> Deref for SerializableLinkedList<T> {
+    type Target = LinkedList<T>;
+
+    fn deref(&self) -> &LinkedList<T> {
+        &self.0
+    }
+}
+
+impl<T> DerefMut for SerializableLinkedList<T> {
+    fn deref_mut(&mut self) -> &mut LinkedList<T> {
+        &mut self.0
+    }
+}
+
+impl<T: HeapSizeOf> HeapSizeOf for SerializableLinkedList<T> {
+    fn heap_size_of_children(&self) -> usize {
+        self.0.heap_size_of_children()
+    }
+}
+
+impl<T> Serialize for SerializableLinkedList<T> where T: Serialize {
+    fn serialize<S>(&self, serializer: &mut S) -> Result<(), S::Error> where S: Serializer {
+        serializer.visit_seq(SeqIteratorVisitor::new(self.0.iter(), Some(self.0.len())))
+    }
+}
+
+impl<T> Deserialize for SerializableLinkedList<T> where T: Deserialize {
+    fn deserialize<D>(deserializer: &mut D) -> Result<SerializableLinkedList<T>, D::Error>
+                      where D: Deserializer {
+        struct SerializableLinkedListVisitor<T> {
+            marker: PhantomData<T>,
+        }
+
+        impl<T> Visitor for SerializableLinkedListVisitor<T> where T: Deserialize {
+            type Value = SerializableLinkedList<T>;
+
+            #[inline]
+            fn visit_seq<V>(&mut self, mut visitor: V)
+                            -> Result<SerializableLinkedList<T>, V::Error>
+                            where V: SeqVisitor {
+                let mut list = LinkedList::new();
+                for _ in 0..visitor.size_hint().0 {
+                    match try!(visitor.visit()) {
+                        Some(element) => list.push_back(element),
+                        None => return Err(Error::end_of_stream_error()),
+                    }
+                }
+                try!(visitor.end());
+                Ok(SerializableLinkedList(list))
+            }
+        }
+
+        deserializer.visit_seq(SerializableLinkedListVisitor {
+            marker: PhantomData,
+        })
+    }
+}
 
 /// Splits the head off a list in O(1) time, and returns the head.
 pub fn split_off_head<T>(list: &mut LinkedList<T>) -> LinkedList<T> {

components/util/opts.rs

@@ -140,6 +140,9 @@ pub struct Opts {
     /// Dumps the display list after a layout.
     pub dump_display_list: bool,
 
+    /// Dumps the display list in JSON form after a layout.
+    pub dump_display_list_json: bool,
+
     /// Dumps the display list after optimization (post layout, at painting time).
     pub dump_display_list_optimized: bool,
 
@@ -178,6 +181,7 @@ pub fn print_debug_usage(app: &str) -> ! {
     print_option("disable-text-aa", "Disable antialiasing of rendered text.");
     print_option("dump-flow-tree", "Print the flow tree after each layout.");
     print_option("dump-display-list", "Print the display list after each layout.");
+    print_option("dump-display-list-json", "Print the display list in JSON form.");
     print_option("dump-display-list-optimized", "Print optimized display list (at paint time).");
     print_option("relayout-event", "Print notifications when there is a relayout.");
     print_option("profile-tasks", "Instrument each task, writing the output to a file.");
@@ -248,6 +252,7 @@ pub fn default_opts() -> Opts {
         user_agent: None,
         dump_flow_tree: false,
         dump_display_list: false,
+        dump_display_list_json: false,
         dump_display_list_optimized: false,
         relayout_event: false,
         validate_display_list_geometry: false,
@@ -424,6 +429,7 @@ pub fn from_cmdline_args(args: &[String]) {
         enable_canvas_antialiasing: !debug_options.contains(&"disable-canvas-aa"),
         dump_flow_tree: debug_options.contains(&"dump-flow-tree"),
         dump_display_list: debug_options.contains(&"dump-display-list"),
+        dump_display_list_json: debug_options.contains(&"dump-display-list-json"),
         dump_display_list_optimized: debug_options.contains(&"dump-display-list-optimized"),
         relayout_event: debug_options.contains(&"relayout-event"),
         validate_display_list_geometry: debug_options.contains(&"validate-display-list-geometry"),

components/util/range.rs

@@ -124,7 +124,7 @@ macro_rules! int_range_index {
 }
 
 /// A range of indices
-#[derive(Clone, RustcEncodable, Copy)]
+#[derive(Clone, RustcEncodable, Copy, Deserialize, Serialize)]
 pub struct Range<I> {
     begin: I,
     length: I,