From db194e74adbd24c9de5545ddf791b8b8f8f53c43 Mon Sep 17 00:00:00 2001
From: Martin Robinson <mrobinson@igalia.com>
Date: Wed, 19 Apr 2023 10:15:58 +0200
Subject: [PATCH] Rename `ComputedValuesExt::establishes_containing_block`

This renames the helper method to be a bit more accurate. For elements
with static, relative, and sticky positioning, their containing block is
always formed by their nearest block container ancestor. This method is
really dealing with style that means an element will establish a
containing block for absolutely positioned descendants.
---
 .../layout_2020/display_list/stacking_context.rs |  5 ++++-
 components/layout_2020/positioned.rs             |  2 +-
 components/layout_2020/style_ext.rs              | 16 ++++++++++++----
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/components/layout_2020/display_list/stacking_context.rs b/components/layout_2020/display_list/stacking_context.rs
index 78992d9c5bc..8cc717569f9 100644
--- a/components/layout_2020/display_list/stacking_context.rs
+++ b/components/layout_2020/display_list/stacking_context.rs
@@ -540,7 +540,10 @@ impl BoxFragment {
         padding_rect: &PhysicalRect<Length>,
         containing_block_info: &mut ContainingBlockInfo,
     ) {
-        if !self.style.establishes_containing_block() {
+        if !self
+            .style
+            .establishes_containing_block_for_absolute_descendants()
+        {
             return;
         }
 
diff --git a/components/layout_2020/positioned.rs b/components/layout_2020/positioned.rs
index 2580d4af9bc..883f783dfd8 100644
--- a/components/layout_2020/positioned.rs
+++ b/components/layout_2020/positioned.rs
@@ -196,7 +196,7 @@ impl PositioningContext {
     pub(crate) fn new_for_style(style: &ComputedValues) -> Option<Self> {
         if style.establishes_containing_block_for_all_descendants() {
             Some(Self::new_for_containing_block_for_all_descendants())
-        } else if style.establishes_containing_block() {
+        } else if style.establishes_containing_block_for_absolute_descendants() {
             Some(Self {
                 for_nearest_positioned_ancestor: Some(Vec::new()),
                 for_nearest_containing_block_for_all_descendants: Vec::new(),
diff --git a/components/layout_2020/style_ext.rs b/components/layout_2020/style_ext.rs
index 58551aedbe6..c1d2f47e2fa 100644
--- a/components/layout_2020/style_ext.rs
+++ b/components/layout_2020/style_ext.rs
@@ -113,7 +113,7 @@ pub(crate) trait ComputedValuesExt {
     fn has_transform_or_perspective(&self) -> bool;
     fn effective_z_index(&self) -> i32;
     fn establishes_stacking_context(&self) -> bool;
-    fn establishes_containing_block(&self) -> bool;
+    fn establishes_containing_block_for_absolute_descendants(&self) -> bool;
     fn establishes_containing_block_for_all_descendants(&self) -> bool;
     fn background_is_transparent(&self) -> bool;
     fn get_webrender_primitive_flags(&self) -> wr::PrimitiveFlags;
@@ -395,7 +395,13 @@ impl ComputedValuesExt for ComputedValues {
         !self.get_position().z_index.is_auto()
     }
 
-    fn establishes_containing_block(&self) -> bool {
+    /// Returns true if this style establishes a containing block for absolute
+    /// descendants (`position: absolute`). If this style happens to establish a
+    /// containing block for “all descendants” (ie including `position: fixed`
+    /// descendants) this method will return true, but a true return value does
+    /// not imply that the style establishes a containing block for all descendants.
+    /// Use `establishes_containing_block_for_all_descendants()` instead.
+    fn establishes_containing_block_for_absolute_descendants(&self) -> bool {
         if self.establishes_containing_block_for_all_descendants() {
             return true;
         }
@@ -403,8 +409,10 @@ impl ComputedValuesExt for ComputedValues {
         self.clone_position() != ComputedPosition::Static
     }
 
-    /// Returns true if this style establishes a containing block for all descendants
-    /// including fixed and absolutely positioned ones.
+    /// Returns true if this style establishes a containing block for
+    /// all descendants, including fixed descendants (`position: fixed`).
+    /// Note that this also implies that it establishes a containing block
+    /// for absolute descendants (`position: absolute`).
     fn establishes_containing_block_for_all_descendants(&self) -> bool {
         if self.get_box().display.outside() != stylo::DisplayOutside::Inline &&
             self.has_transform_or_perspective()