Don't let a deferred float inflate its block formatting context

tests/layout/test_float.py

@@ -302,6 +302,42 @@ def test_floats_page_breaks_3():
     assert positions_y == [[10, 40], [10, 40], [10]]
 
 
+@assert_no_logs
+def test_float_overflow_splits_formatting_context():
+    # A deferred (overflowing) float must not inflate its block formatting
+    # context on the current page, or the whole block is pushed to the next page
+    # instead of being split across the page break.
+    page_1, page_2 = render_pages('''
+      <style>@page { size: 100px }</style>
+      <div style="height: 70px"></div>
+      <div style="display: flow-root">
+        <p style="height: 20px">a</p>
+        <div style="float: right; width: 30px; height: 40px"></div>
+        <p>b</p>
+      </div>
+    ''')
+
+    # Page 1 keeps the spacer and the first paragraph: the block is split, not
+    # deferred whole.
+    html, = page_1.children
+    body, = html.children
+    spacer, bfc_1 = body.children
+    assert spacer.height == 70
+    paragraph_a, = bfc_1.children
+    assert paragraph_a.element_tag == 'p'
+    assert paragraph_a.position_y == 70
+
+    # Page 2 resumes the block with the deferred float and the last paragraph.
+    html, = page_2.children
+    body, = html.children
+    bfc_2, = body.children
+    float_box, paragraph_b = bfc_2.children
+    assert float_box.is_floated()
+    assert float_box.position_y == 0
+    assert paragraph_b.element_tag == 'p'
+    assert paragraph_b.position_y == 0
+
+
 @assert_no_logs
 def test_preferred_widths_1():
     def get_float_width(body_width):

weasyprint/layout/block.py

@@ -285,6 +285,7 @@ def _out_of_flow_layout(context, box, index, child, new_children,
             resume_at = {index: None}
             out_of_flow_resume_at = None
             stop = True
+            remove_placeholders(context, [new_child], absolute_boxes, fixed_boxes)
             if new_children and avoid_page_break(page_break, context):
                 # Can’t break inside float, find an earlier page break.
                 result = find_earlier_page_break(
@@ -1106,8 +1107,7 @@ def remove_placeholders(context, box_list, absolute_boxes, fixed_boxes):
     """
     for box in box_list:
         if isinstance(box, boxes.ParentBox):
-            remove_placeholders(
-                context, box.children, absolute_boxes, fixed_boxes)
+            remove_placeholders(context, box.children, absolute_boxes, fixed_boxes)
         if box.style['position'] == 'absolute' and box in absolute_boxes:
             absolute_boxes.remove(box)
         elif box.style['position'] == 'fixed' and box in fixed_boxes:
@@ -1116,6 +1116,8 @@ def remove_placeholders(context, box_list, absolute_boxes, fixed_boxes):
             context.unlayout_footnote(box.footnote)
         if box in context.broken_out_of_flow:
             context.broken_out_of_flow.pop(box)
+        if box in context.excluded_shapes:
+            context.excluded_shapes.remove(box)
 
 
 def avoid_page_break(page_break, context):