Don’t crash when currentColor is set on root svg tag

Fix #1740.

tests/draw/test_current_color.py

@@ -1,5 +1,7 @@
 """Test the currentColor value."""
 
+import pytest
+
 from ..testing_utils import assert_no_logs
 
 
@@ -50,3 +52,31 @@ def test_current_color_4(assert_pixels):
                 color: lime; border: 1px solid; border-color: inherit }
       </style>
       <table><td>''')
+
+
+@assert_no_logs
+def test_current_color_svg_1(assert_pixels):
+    assert_pixels('KK\nKK', '''
+      <style>
+        @page { size: 2px }
+        svg { display: block }
+      </style>
+      <svg xmlns="http://www.w3.org/2000/svg"
+           width="2" height="2" fill="currentColor">
+        <rect width="2" height="2"></rect>
+      </svg>''')
+
+
+@pytest.mark.xfail
+@assert_no_logs
+def test_current_color_svg_2(assert_pixels):
+    assert_pixels('GG\nGG', '''
+      <style>
+        @page { size: 2px }
+        svg { display: block }
+        body { color: lime }
+      </style>
+      <svg xmlns="http://www.w3.org/2000/svg"
+           width="2" height="2">
+        <rect width="2" height="2" fill="currentColor"></rect>
+      </svg>''')

weasyprint/svg/__init__.py

@@ -288,6 +288,11 @@ class SVG:
         self.tree = Node(wrapper, style)
         self.url = url
 
+        # Replace 'currentColor' value
+        for key in COLOR_ATTRIBUTES:
+            if self.tree.get(key) == 'currentColor':
+                self.tree.attrib[key] = self.tree.get('color', 'black')
+
         self.filters = {}
         self.gradients = {}
         self.images = {}