Don’t crash when grid items have auto margins

Auto margins are not handled (there already was a TODO for this), but at least
it doesn’t crash anymore.

Fix #2154.

tests/layout/test_grid.py

@@ -835,3 +835,24 @@ def test_grid_margin():
     assert div_b.height == 4
     assert div_c.height == 6
     assert article.height == 10
+
+
+@assert_no_logs
+def test_grid_item_margin():
+    # Regression test for https://github.com/Kozea/WeasyPrint/issues/2154
+    page, = render_pages('''
+      <style>
+        @font-face { src: url(weasyprint.otf); font-family: weasyprint }
+        article { display: grid }
+        div { margin: auto }
+      </style>
+      <article>
+        <div>a</div>
+        <div>b</div>
+      </article>
+    ''')
+    html, = page.children
+    body, = html.children
+    article, = body.children
+    div_a, div_b = article.children
+    # TODO: Test auto margin values.

weasyprint/layout/grid.py

@@ -1119,6 +1119,17 @@ def grid_layout(context, box, bottom_space, skip_stack, containing_block,
         height = (
             sum(size for size, _ in rows_sizes[y:y+height]) +
             (height - 1) * row_gap)
+
+        # TODO: Apply auto margin.
+        if child.margin_top == 'auto':
+            child.margin_top = 0
+        if child.margin_right == 'auto':
+            child.margin_right = 0
+        if child.margin_bottom == 'auto':
+            child.margin_bottom = 0
+        if child.margin_left == 'auto':
+            child.margin_left = 0
+
         child_width = width - (
             child.margin_left + child.border_left_width + child.padding_left +
             child.margin_right + child.border_right_width + child.padding_right)
@@ -1156,7 +1167,6 @@ def grid_layout(context, box, bottom_space, skip_stack, containing_block,
             # TODO: Support fragmentation in grid rows.
             continue
 
-        # TODO: Apply auto margins.
         if justify_self & {'normal', 'stretch'}:
             new_child.width = max(child_width, new_child.width)
         else: