Auto merge of #29927 - Loirooriol:bfc-root-contain-floats, r=mrobinson

Increase BFC root height to contain floats

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #29823
- [X] There are tests for these changes

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components/layout_2020/flow/mod.rs

@@ -96,10 +96,18 @@ impl BlockFormattingContext {
                 .collapsed_through
         );
 
+        // The content height of a BFC root should include any float participating in that BFC
+        // (https://drafts.csswg.org/css2/#root-height), we implement this by imagining there is
+        // an element with `clear: both` after the actual contents.
+        let clearance = sequential_layout_state.map_or(Length::zero(), |sequential_layout_state| {
+            sequential_layout_state.calculate_clearance(ClearSide::Both)
+        });
+
         IndependentLayout {
             fragments: flow_layout.fragments,
             content_block_size: flow_layout.content_block_size +
-                flow_layout.collapsible_margins_in_children.end.solve(),
+                flow_layout.collapsible_margins_in_children.end.solve() +
+                clearance,
         }
     }
 }

tests/wpt/meta/css/CSS2/floats-clear/float-replaced-height-001.xht.ini

@@ -1,2 +0,0 @@
-[float-replaced-height-001.xht]
-  expected: FAIL

tests/wpt/meta/css/CSS2/floats-clear/floats-005.xht.ini

@@ -1,2 +0,0 @@
-[floats-005.xht]
-  expected: FAIL

tests/wpt/meta/css/CSS2/floats-clear/floats-101.xht.ini

@@ -1,2 +0,0 @@
-[floats-101.xht]
-  expected: FAIL

tests/wpt/meta/css/CSS2/floats-clear/floats-145.xht.ini

@@ -1,2 +0,0 @@
-[floats-145.xht]
-  expected: FAIL

tests/wpt/meta/css/CSS2/normal-flow/block-formatting-context-height-001.xht.ini

@@ -1,2 +0,0 @@
-[block-formatting-context-height-001.xht]
-  expected: FAIL

tests/wpt/meta/css/CSS2/normal-flow/block-formatting-context-height-002.xht.ini

@@ -1,2 +0,0 @@
-[block-formatting-context-height-002.xht]
-  expected: FAIL

tests/wpt/meta/css/css-flexbox/change-column-flex-width.html.ini

@@ -1,3 +0,0 @@
-[change-column-flex-width.html]
-  [#container 1]
-    expected: FAIL

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

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

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

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

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

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