Allow dumping the fragment tree in layout_2020

This is done when the dump-flow-tree debug option is passed.

components/layout_2020/flow/root.rs

@@ -17,6 +17,7 @@ use crate::replaced::ReplacedContent;
 use crate::sizing::ContentSizesRequest;
 use crate::style_ext::{Display, DisplayGeneratingBox, DisplayInside};
 use crate::DefiniteContainingBlock;
+use gfx_traits::print_tree::PrintTree;
 use script_layout_interface::wrapper_traits::LayoutNode;
 use servo_arc::Arc;
 use style::properties::ComputedValues;
@@ -154,4 +155,11 @@ impl FragmentTreeRoot {
             fragment.build_display_list(builder, &containing_block)
         }
     }
+
+    pub fn print(&self) {
+        let mut print_tree = PrintTree::new("Fragment Tree".to_string());
+        for fragment in &self.0 {
+            fragment.print(&mut print_tree);
+        }
+    }
 }

components/layout_2020/fragments.rs

@@ -4,6 +4,7 @@
 
 use crate::geom::flow_relative::{Rect, Sides, Vec2};
 use gfx::text::glyph::GlyphStore;
+use gfx_traits::print_tree::PrintTree;
 use servo_arc::Arc as ServoArc;
 use std::sync::Arc;
 use style::dom::OpaqueNode;
@@ -80,6 +81,15 @@ impl Fragment {
             Fragment::Image(f) => &mut f.rect.start_corner,
         }
     }
+
+    pub fn print(&self, tree: &mut PrintTree) {
+        match self {
+            Fragment::Box(fragment) => fragment.print(tree),
+            Fragment::Anonymous(fragment) => fragment.print(tree),
+            Fragment::Text(fragment) => fragment.print(tree),
+            Fragment::Image(fragment) => fragment.print(tree),
+        }
+    }
 }
 
 impl AnonymousFragment {
@@ -90,13 +100,67 @@ impl AnonymousFragment {
             mode,
         }
     }
+
+    pub fn print(&self, tree: &mut PrintTree) {
+        tree.new_level(format!(
+            "Anonymous\
+                \nrect={:?}",
+            self.rect
+        ));
+
+        for child in &self.children {
+            child.print(tree);
+        }
+        tree.end_level();
+    }
 }
 
 impl BoxFragment {
+    pub fn padding_rect(&self) -> Rect<Length> {
+        self.content_rect.inflate(&self.padding)
+    }
+
     pub fn border_rect(&self) -> Rect<Length> {
-        self.content_rect
-            .inflate(&self.padding)
-            .inflate(&self.border)
+        self.padding_rect().inflate(&self.border)
+    }
+
+    pub fn print(&self, tree: &mut PrintTree) {
+        tree.new_level(format!(
+            "Box\
+                \ncontent={:?}\
+                \npadding rect={:?}\
+                \nborder rect={:?}",
+            self.content_rect,
+            self.padding_rect(),
+            self.border_rect()
+        ));
+
+        for child in &self.children {
+            child.print(tree);
+        }
+        tree.end_level();
+    }
+}
+
+impl TextFragment {
+    pub fn print(&self, tree: &mut PrintTree) {
+        tree.add_item(format!(
+            "Text num_glyphs={}",
+            self.glyphs
+                .iter()
+                .map(|glyph_store| glyph_store.len().0)
+                .sum::<isize>()
+        ));
+    }
+}
+
+impl ImageFragment {
+    pub fn print(&self, tree: &mut PrintTree) {
+        tree.add_item(format!(
+            "Image\
+                \nrect={:?}",
+            self.rect
+        ));
     }
 }
 

components/layout_2020/geom.rs

@@ -45,7 +45,7 @@ pub(crate) mod flow_relative {
         pub block: T,
     }
 
-    #[derive(Clone, Debug)]
+    #[derive(Clone)]
     pub(crate) struct Rect<T> {
         pub start_corner: Vec2<T>,
         pub size: Vec2<T>,
@@ -200,6 +200,19 @@ impl flow_relative::Rect<Length> {
     }
 }
 
+impl fmt::Debug for flow_relative::Rect<Length> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "Rect(i{}×b{} @ (i{},b{}))",
+            self.size.inline.px(),
+            self.size.block.px(),
+            self.start_corner.inline.px(),
+            self.start_corner.block.px(),
+        )
+    }
+}
+
 impl<T: Clone> flow_relative::Vec2<T> {
     pub fn size_to_physical(&self, mode: WritingMode) -> physical::Vec2<T> {
         // https://drafts.csswg.org/css-writing-modes/#logical-to-physical

components/layout_thread_2020/lib.rs

@@ -213,6 +213,9 @@ pub struct LayoutThread {
 
     /// Emits notifications when there is a relayout.
     relayout_event: bool,
+
+    /// Dumps the fragment tree after a layout.
+    dump_fragment_tree: bool,
 }
 
 impl LayoutThreadFactory for LayoutThread {
@@ -246,7 +249,7 @@ impl LayoutThreadFactory for LayoutThread {
         relayout_event: bool,
         _nonincremental_layout: bool,
         _trace_layout: bool,
-        _dump_flow_tree: bool,
+        dump_flow_tree: bool,
     ) {
         thread::Builder::new()
             .name(format!("LayoutThread {:?}", id))
@@ -287,6 +290,7 @@ impl LayoutThreadFactory for LayoutThread {
                         load_webfonts_synchronously,
                         window_size,
                         relayout_event,
+                        dump_flow_tree,
                     );
 
                     let reporter_name = format!("layout-reporter-{}", id);
@@ -449,6 +453,7 @@ impl LayoutThread {
         load_webfonts_synchronously: bool,
         window_size: WindowSizeData,
         relayout_event: bool,
+        dump_fragment_tree: bool,
     ) -> LayoutThread {
         // Let webrender know about this pipeline by sending an empty display list.
         webrender_api_sender.send_initial_transaction(webrender_document, id.to_webrender());
@@ -527,6 +532,7 @@ impl LayoutThread {
             busy,
             load_webfonts_synchronously,
             relayout_event,
+            dump_fragment_tree,
         }
     }
 
@@ -1292,6 +1298,10 @@ impl LayoutThread {
         let mut display_list = DisplayListBuilder::new(self.id.to_webrender(), viewport_size);
         fragment_tree.build_display_list(&mut display_list, viewport_size);
 
+        if self.dump_fragment_tree {
+            fragment_tree.print();
+        }
+
         debug!("Layout done!");
 
         let mut epoch = self.epoch.get();