Split line layout into two phases (#30089)

In the first phase, we gather LineItems and then when we have enough to
form a line we turn them into Fragments. This will make it possible to
more simply implement `vertical-align` and `text-align: justify` because
we need to measure the different aspects of the candidate line and then
produce a Fragments.

This is a general refactor of the way that inline layout works, so comes
with some progressions. In addition there are some new failures.

New failures:

Some tests are now failing because only the test or reference is getting
proper line height when it wasn't before. These should be fixed in a
followup change that properly calculate line-height in more cases:

 - /_mozilla/css/list_style_position_a.html
 - /css/CSS2/floats/float-no-content-beside-001.html
 - /css/css-content/pseudo-element-inline-box.html
 - /css/css-flexbox/flexbox_flex-none-wrappable-content.html

Some tests are now failing because floats are now placed properly, but
are no longer in their inline box stacking contexts. These will be fixed
by a followup change which properly parents them:

- /css/filter-effects/filtered-inline-applies-to-float.html.ini
- /css/css-color/inline-opacity-float-child.html.ini

One test is failing due to floating point precision errors:

- /css/CSS2/floats-clear/floats-141.xht.ini

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Mukilan Thiyagarajan <mukilan@igalia.com>

components/layout_2020/flow/mod.rs

@@ -372,6 +372,7 @@ impl BlockContainer {
                 positioning_context,
                 containing_block,
                 sequential_layout_state,
+                collapsible_with_parent_start_margin,
             ),
         }
     }

components/layout_2020/fragment_tree/box_fragment.rs

@@ -155,6 +155,7 @@ impl BoxFragment {
                 \ncontent={:?}\
                 \npadding rect={:?}\
                 \nborder rect={:?}\
+                \nmargin={:?}\
                 \nclearance={:?}\
                 \nscrollable_overflow={:?}\
                 \noverflow={:?} / {:?}",
@@ -162,6 +163,7 @@ impl BoxFragment {
             self.content_rect,
             self.padding_rect(),
             self.border_rect(),
+            self.margin,
             self.clearance,
             self.scrollable_overflow(&PhysicalRect::zero()),
             self.style.get_box().overflow_x,

components/layout_2020/fragment_tree/fragment.rs

@@ -299,11 +299,12 @@ impl AnonymousFragment {
 impl TextFragment {
     pub fn print(&self, tree: &mut PrintTree) {
         tree.add_item(format!(
-            "Text num_glyphs={}",
+            "Text num_glyphs={} box={:?}",
             self.glyphs
                 .iter()
                 .map(|glyph_store| glyph_store.len().0)
-                .sum::<isize>()
+                .sum::<isize>(),
+            self.rect,
         ));
     }
 }

components/layout_2020/geom.rs

@@ -32,7 +32,7 @@ pub mod flow_relative {
         pub size: Vec2<T>,
     }
 
-    #[derive(Clone, Serialize)]
+    #[derive(Clone, Debug, Serialize)]
     pub struct Sides<T> {
         pub inline_start: T,
         pub inline_end: T,

components/layout_2020/positioned.rs

@@ -229,11 +229,8 @@ impl PositioningContext {
         new_context.layout_collected_children(layout_context, &mut new_fragment);
 
         // If the new context has any hoisted boxes for the nearest containing block for
-        // all descendants than collect them and pass them up the tree.
+        // pass them up the tree.
-        vec_append_owned(
+        self.append(new_context);
-            &mut self.for_nearest_containing_block_for_all_descendants,
-            new_context.for_nearest_containing_block_for_all_descendants,
-        );
 
         if style.clone_position() == Position::Relative {
             new_fragment.content_rect.start_corner +=
@@ -305,16 +302,38 @@ impl PositioningContext {
             .push(box_)
     }
 
+    fn is_empty(&self) -> bool {
+        self.for_nearest_containing_block_for_all_descendants
+            .is_empty() &&
+            self.for_nearest_positioned_ancestor
+                .as_ref()
+                .map_or(true, |vector| vector.is_empty())
+    }
+
     pub(crate) fn append(&mut self, other: Self) {
+        if other.is_empty() {
+            return;
+        }
+
         vec_append_owned(
             &mut self.for_nearest_containing_block_for_all_descendants,
             other.for_nearest_containing_block_for_all_descendants,
         );
+
         match (
             self.for_nearest_positioned_ancestor.as_mut(),
             other.for_nearest_positioned_ancestor,
         ) {
-            (Some(a), Some(b)) => vec_append_owned(a, b),
+            (Some(us), Some(them)) => vec_append_owned(us, them),
+            (None, Some(them)) => {
+                // This is the case where we have laid out the absolute children in a containing
+                // block for absolutes and we then are passing up the fixed-position descendants
+                // to the containing block for all descendants.
+                vec_append_owned(
+                    &mut self.for_nearest_containing_block_for_all_descendants,
+                    them,
+                );
+            },
             (None, None) => {},
             _ => unreachable!(),
         }
@@ -378,6 +397,7 @@ impl PositioningContext {
 }
 
 /// A data structure which stores the size of a positioning context.
+#[derive(PartialEq)]
 pub(crate) struct PositioningContextLength {
     /// The number of boxes that will be hoisted the the nearest positioned ancestor for
     /// layout.

components/layout_2020/style_ext.rs

@@ -55,6 +55,7 @@ pub(crate) enum DisplayInside {
 }
 
 /// Percentages resolved but not `auto` margins
+#[derive(Clone)]
 pub(crate) struct PaddingBorderMargin {
     pub padding: flow_relative::Sides<Length>,
     pub border: flow_relative::Sides<Length>,

tests/wpt/meta/css/CSS2/abspos/remove-block-between-inline-and-abspos.html.ini

@@ -1,2 +0,0 @@
-[remove-block-between-inline-and-abspos.html]
-  expected: FAIL

tests/wpt/meta/css/CSS2/box-display/block-in-inline-007.xht.ini

@@ -1,2 +0,0 @@
-[block-in-inline-007.xht]
-  expected: FAIL

tests/wpt/meta/css/CSS2/floats-clear/floats-141.xht.ini

@@ -0,0 +1,2 @@
+[floats-141.xht]
+  expected: FAIL

tests/wpt/meta/css/CSS2/floats/float-no-content-beside-001.html.ini

@@ -0,0 +1,2 @@
+[float-no-content-beside-001.html]
+  expected: FAIL

tests/wpt/meta/css/CSS2/floats/float-nowrap-4.html.ini

@@ -1,2 +0,0 @@
-[float-nowrap-4.html]
-  expected: FAIL

tests/wpt/meta/css/CSS2/floats/floats-placement-vertical-001b.xht.ini

@@ -1,2 +0,0 @@
-[floats-placement-vertical-001b.xht]
-  expected: FAIL

tests/wpt/meta/css/CSS2/floats/floats-placement-vertical-001c.xht.ini

@@ -1,2 +0,0 @@
-[floats-placement-vertical-001c.xht]
-  expected: FAIL

tests/wpt/meta/css/CSS2/normal-flow/block-non-replaced-width-007.xht.ini

@@ -1,2 +0,0 @@
-[block-non-replaced-width-007.xht]
-  expected: FAIL

tests/wpt/meta/css/CSS2/text/text-indent-on-blank-line-rtl-left-align.html.ini

@@ -1,2 +0,0 @@
-[text-indent-on-blank-line-rtl-left-align.html]
-  expected: FAIL

tests/wpt/meta/css/CSS2/text/white-space-008.xht.ini

@@ -1,2 +0,0 @@
-[white-space-008.xht]
-  expected: FAIL

tests/wpt/meta/css/CSS2/text/white-space-normal-007.xht.ini

@@ -1,2 +0,0 @@
-[white-space-normal-007.xht]
-  expected: FAIL

tests/wpt/meta/css/CSS2/zindex/stack-floats-003.xht.ini

@@ -1,2 +0,0 @@
-[stack-floats-003.xht]
-  expected: FAIL

tests/wpt/meta/css/css-color/inline-opacity-float-child.html.ini

@@ -0,0 +1,2 @@
+[inline-opacity-float-child.html]
+  expected: FAIL

tests/wpt/meta/css/css-content/pseudo-element-inline-box.html.ini

@@ -0,0 +1,2 @@
+[pseudo-element-inline-box.html]
+  expected: FAIL

tests/wpt/meta/css/css-flexbox/flexbox_flex-none-wrappable-content.html.ini

@@ -0,0 +1,2 @@
+[flexbox_flex-none-wrappable-content.html]
+  expected: FAIL

tests/wpt/meta/css/css-position/position-relative-003.html.ini

@@ -1,2 +0,0 @@
-[position-relative-003.html]
-  expected: TIMEOUT

tests/wpt/meta/css/css-position/position-relative-004.html.ini

@@ -1,2 +0,0 @@
-[position-relative-004.html]
-  expected: TIMEOUT

tests/wpt/meta/css/filter-effects/filtered-inline-applies-to-float.html.ini

@@ -0,0 +1,2 @@
+[filtered-inline-applies-to-float.html]
+  expected: FAIL

tests/wpt/mozilla/meta/css/input_whitespace.html.ini

@@ -1,2 +0,0 @@
-[input_whitespace.html]
-  expected: FAIL

tests/wpt/mozilla/meta/css/list_style_position_a.html.ini

@@ -0,0 +1,2 @@
+[list_style_position_a.html]
+  expected: FAIL