layout: Avoid layout sometimes when stretching (#33967)

This is the second flexbox caching change. It seeks to detect when a
relayout can be avoided in the case of a stretching flex item. This
heuristic can be combined, because currently we still do relayout
sometimes when we do not need to.

For instance currently we always relayout when a flex child is itself a
column flex. This only needs to happen when the grandchildren themselves
grow or shrink. That optimization is perhaps a lower priority as
`flex-grow: 0 / flex-shrink: 1` is the default behavior for flex.

Since this change means we more consistenly zero out the percentage part
of `calc` expressions when they have circular dependencies, this causes one
test to start failing (`/css/css-values/calc-min-height-block-1.html`).
This is related to w3c/csswg-drafts#10969, which is pending on further
discussion in the working group.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/components/layout_2020/flow/inline/mod.rs b/components/layout_2020/flow/inline/mod.rs
index 4bad4293e5a..73c678e0458 100644
--- a/components/layout_2020/flow/inline/mod.rs
+++ b/components/layout_2020/flow/inline/mod.rs
@@ -627,6 +627,10 @@ pub(super) struct InlineFormattingContextLayout<'layout_data> {
     /// Whether or not this InlineFormattingContext has processed any in flow content at all.
     had_inflow_content: bool,
 
+    /// Whether or not the layout of this InlineFormattingContext depends on the block size
+    /// of its container for the purposes of flexbox layout.
+    depends_on_block_constraints: bool,
+
     /// The currently white-space-collapse setting of this line. This is stored on the
     /// [`InlineFormattingContextLayout`] because when a soft wrap opportunity is defined
     /// by the boundary between two characters, the white-space-collapse property of their
@@ -701,6 +705,12 @@ impl<'layout_dta> InlineFormattingContextLayout<'layout_dta> {
                 .map(|index| &self.ifc.font_metrics[index].metrics),
         );
 
+        self.depends_on_block_constraints |= inline_box
+            .style
+            .depends_on_block_constraints_due_to_relative_positioning(
+                self.containing_block.style.writing_mode,
+            );
+
         // If we are starting a `<br>` element prepare to clear after its deferred linebreak has been
         // processed. Note that a `<br>` is composed of the element itself and the inner pseudo-element
         // with the actual linebreak. Both will have this `FragmentFlag`; that's why this code only
@@ -1631,6 +1641,7 @@ impl InlineFormattingContext {
             deferred_br_clear: Clear::None,
             have_deferred_soft_wrap_opportunity: false,
             had_inflow_content: false,
+            depends_on_block_constraints: false,
             white_space_collapse: style_text.white_space_collapse,
             text_wrap_mode: style_text.text_wrap_mode,
             baselines: Baselines::default(),
@@ -1692,6 +1703,7 @@ impl InlineFormattingContext {
             content_block_size,
             collapsible_margins_in_children,
             baselines: layout.baselines,
+            depends_on_block_constraints: layout.depends_on_block_constraints,
         }
     }
 
@@ -1921,6 +1933,12 @@ impl IndependentFormattingContext {
             layout.containing_block,
         );
 
+        // If this Fragment's layout depends on the block size of the containing block,
+        // then the entire layout of the inline formatting context does as well.
+        layout.depends_on_block_constraints |= fragment.base.flags.contains(
+            FragmentFlags::SIZE_DEPENDS_ON_BLOCK_CONSTRAINTS_AND_CAN_BE_CHILD_OF_FLEX_ITEM,
+        );
+
         // Offset the content rectangle by the physical offset of the padding, border, and margin.
         let container_writing_mode = layout.containing_block.style.writing_mode;
         let pbm_physical_offset = pbm_sums