Avoid endless recursion for variables in nested functions

Fix #2370.

tests/css/test_variables.py

@@ -488,6 +488,21 @@ def test_variable_in_function():
     assert div2.children[0].children[0].children[0].text == '2'
 
 
+@assert_no_logs
+def test_variable_in_nested_function():
+    page, = render_pages('''
+      <style>
+        body { --var: 255 0 0 }
+        div { background-image: linear-gradient(rgba(var(--var))) }
+      </style>
+      <div></div>
+    ''')
+    html, = page.children
+    body, = html.children
+    div, = body.children
+    assert div.style['background_image'][0][1].colors[0] == (1, 0, 0, 1)
+
+
 @assert_no_logs
 def test_variable_in_function_multiple_values():
     page, = render_pages('''

weasyprint/css/__init__.py

@@ -581,7 +581,7 @@ def resolve_var(computed, token, parent_style):
     if token.lower_name != 'var':
         arguments = []
         for i, argument in enumerate(token.arguments):
-            if argument.type == 'function' and argument.lower_name == 'var':
+            if argument.type == 'function':
                 arguments.extend(resolve_var(computed, argument, parent_style))
             else:
                 arguments.append(argument)