Make items overflowing grid wrap to the next row/column

Fix #2184.

tests/layout/test_grid.py

@@ -280,6 +280,40 @@ def test_grid_template_areas_overlap():
     assert article.width == 10
 
 
+@assert_no_logs
+def test_grid_template_areas_span_overflow():
+    page, = render_pages('''
+      <style>
+        @font-face { src: url(weasyprint.otf); font-family: weasyprint }
+        article {
+          display: grid;
+          font-family: weasyprint;
+          font-size: 2px;
+          grid-template-columns: 50% 50%;
+          line-height: 1;
+          width: 10px;
+        }
+      </style>
+      <article>
+        <div style="">a</div>
+        <div style="grid-column: span 2">a</div>
+        <div style="">a</div>
+      </article>
+    ''')
+    html, = page.children
+    body, = html.children
+    article, = body.children
+    div_a1, div_a2, div_a3 = article.children
+    assert div_a1.position_x == div_a2.position_x == div_a3.position_x == 0
+    assert div_a1.position_y == 0
+    assert div_a2.position_y == 2
+    assert div_a3.position_y == 4
+    assert div_a1.width == div_a3.width == 5
+    assert div_a2.width == 10
+    assert div_a1.height == div_a2.height == div_a3.height == 2
+    assert article.width == 10
+
+
 @assert_no_logs
 def test_grid_template_areas_extra_span():
     page, = render_pages('''

weasyprint/layout/grid.py

@@ -842,8 +842,9 @@ def grid_layout(context, box, bottom_space, skip_stack, containing_block,
                             width, height = first_size, second_size
                         intersect = _intersect_with_children(
                             x, y, width, height, children_positions.values())
-                        if intersect:
-                            # Child intersects with a positioned child.
+                        overflow = second_i + second_size > implicit_second_2
+                        if intersect or overflow:
+                            # Child intersects with a positioned child or overflows.
                             continue
                         else:
                             # Free place found.
@@ -947,8 +948,9 @@ def grid_layout(context, box, bottom_space, skip_stack, containing_block,
                             width, height = first_size, second_size
                         intersect = _intersect_with_children(
                             x, y, width, height, children_positions.values())
-                        if intersect:
-                            # Child intersects with a positioned child.
+                        overflow = second_i + second_size > implicit_second_2
+                        if intersect or overflow:
+                            # Child intersects with a positioned child or overflows.
                             continue
                         else:
                             # Free place found.