Check xlink:href for gradientUnits="userSpaceOnUse"

When considering to prune attributes set to a default values, we
checked the `gradientUnits` attribute first to determine if that was
valid. Unfortunately, we omitted to check whether the `gradientUnits`
attribute was inherited via `xlink:ref`.  This commit corrects that
bug.

Closes: scour-project#225
Signed-off-by: Niels Thykier <[email protected]>

scour/scour.py

@@ -1931,6 +1931,36 @@ def mayContainTextNodes(node):
     return result
 
 
+def _gradient_units_is_not_user_space(node):
+    current_node = node
+    doc = None
+    while True:
+        gradient_unit = node.getAttribute('gradientUnits')
+        if gradient_unit != '':
+            # The current node has a value, then it decides
+            break
+
+        # The current node did not have value - check if we reference
+        # another node that might have it.
+        href = current_node.getAttributeNS(NS['XLINK'], 'href')
+        if href == '' or not href.startswith('#'):
+            return True
+        if doc is None:
+            doc = current_node.ownerDocument
+            # Should not happen in practise as our nodes should
+            # always be attached to a document.  However, if it
+            # does, then we assume we can strip the attribute.
+            if doc is None:
+                return True
+        current_node = doc.getElementById(href[1:])
+        if current_node is None:
+            # Assume we can strip the attribute when we cannot find
+            # the other node
+            return True
+
+    return gradient_unit != 'userSpaceOnUse'
+
+
 # A list of default attributes that are safe to remove if all conditions are fulfilled
 #
 # Each default attribute is an object of type 'DefaultAttribute' with the following fields:
@@ -2006,38 +2036,38 @@ def mayContainTextNodes(node):
     # filters and masks
     DefaultAttribute('x', -10, Unit.PCT, ['filter', 'mask']),
     DefaultAttribute('x', -0.1, Unit.NONE, ['filter', 'mask'],
-                     conditions=lambda node: node.getAttribute('gradientUnits') != 'userSpaceOnUse'),
+                     conditions=_gradient_units_is_not_user_space),
     DefaultAttribute('y', -10, Unit.PCT, ['filter', 'mask']),
     DefaultAttribute('y', -0.1, Unit.NONE, ['filter', 'mask'],
-                     conditions=lambda node: node.getAttribute('gradientUnits') != 'userSpaceOnUse'),
+                     conditions=_gradient_units_is_not_user_space),
     DefaultAttribute('width', 120, Unit.PCT, ['filter', 'mask']),
     DefaultAttribute('width', 1.2, Unit.NONE, ['filter', 'mask'],
-                     conditions=lambda node: node.getAttribute('gradientUnits') != 'userSpaceOnUse'),
+                     conditions=_gradient_units_is_not_user_space),
     DefaultAttribute('height', 120, Unit.PCT, ['filter', 'mask']),
     DefaultAttribute('height', 1.2, Unit.NONE, ['filter', 'mask'],
-                     conditions=lambda node: node.getAttribute('gradientUnits') != 'userSpaceOnUse'),
+                     conditions=_gradient_units_is_not_user_space),
 
     # gradients
     DefaultAttribute('x1', 0, elements=['linearGradient']),
     DefaultAttribute('y1', 0, elements=['linearGradient']),
     DefaultAttribute('y2', 0, elements=['linearGradient']),
     DefaultAttribute('x2', 100, Unit.PCT, elements=['linearGradient']),
     DefaultAttribute('x2', 1, Unit.NONE, elements=['linearGradient'],
-                     conditions=lambda node: node.getAttribute('gradientUnits') != 'userSpaceOnUse'),
+                     conditions=_gradient_units_is_not_user_space),
     # remove fx/fy before cx/cy to catch the case where fx = cx = 50% or fy = cy = 50% respectively
     DefaultAttribute('fx', elements=['radialGradient'],
                      conditions=lambda node: node.getAttribute('fx') == node.getAttribute('cx')),
     DefaultAttribute('fy', elements=['radialGradient'],
                      conditions=lambda node: node.getAttribute('fy') == node.getAttribute('cy')),
     DefaultAttribute('r',  50, Unit.PCT, elements=['radialGradient']),
     DefaultAttribute('r',  0.5, Unit.NONE, elements=['radialGradient'],
-                     conditions=lambda node: node.getAttribute('gradientUnits') != 'userSpaceOnUse'),
+                     conditions=_gradient_units_is_not_user_space),
     DefaultAttribute('cx', 50, Unit.PCT, elements=['radialGradient']),
     DefaultAttribute('cx', 0.5, Unit.NONE, elements=['radialGradient'],
-                     conditions=lambda node: node.getAttribute('gradientUnits') != 'userSpaceOnUse'),
+                     conditions=_gradient_units_is_not_user_space),
     DefaultAttribute('cy', 50, Unit.PCT, elements=['radialGradient']),
     DefaultAttribute('cy', 0.5, Unit.NONE, elements=['radialGradient'],
-                     conditions=lambda node: node.getAttribute('gradientUnits') != 'userSpaceOnUse'),
+                     conditions=_gradient_units_is_not_user_space),
     DefaultAttribute('spreadMethod', 'pad', elements=['linearGradient', 'radialGradient']),
 
     # filter effects

test_scour.py

@@ -1517,8 +1517,21 @@ def runTest(self):
 class RemoveDefaultGradX1Value(unittest.TestCase):
 
     def runTest(self):
-        g = scourXmlFile('unittests/gradient-default-attrs.svg').getElementById('grad1')
-        self.assertEqual(g.getAttribute('x1'), '',
+        doc = scourXmlFile('unittests/gradient-default-attrs.svg')
+        g1 = doc.getElementById('grad1')
+        g1b = doc.getElementById('grad1b')
+        g1c = doc.getElementById('grad1c')
+        g1d = doc.getElementById('grad1d')
+        g1e = doc.getElementById('grad1e')
+        self.assertEqual(g1.getAttribute('x1'), '',
+                         'x1="0" not removed')
+        self.assertEqual(g1b.getAttribute('x1'), '',
+                         'x1="0" not removed')
+        self.assertEqual(g1c.getAttribute('x1'), '',
+                         'x1="0" removed (but should not be due to gradientUnits)')
+        self.assertEqual(g1d.getAttribute('x1'), '',
+                         'x1="0" removed (but should not be due to href)')
+        self.assertEqual(g1e.getAttribute('x1'), '',
                          'x1="0" not removed')