Fix permalink for multiline Python signatures

Author: TLouf

sphinx/domains/python.py

@@ -504,6 +504,8 @@ def handle_signature(self, sig: str, signode: desc_signature) -> Tuple[str, str]
             and len(sig) > max_len
         )
         signode['is_multiline'] = multiline
+        if multiline:
+            signode['add_permalink'] = True
 
         sig_prefix = self.get_signature_prefix(sig)
         if sig_prefix:

sphinx/writers/html5.py

@@ -93,7 +93,7 @@ def visit_desc_signature(self, node: Element) -> None:
 
     def depart_desc_signature(self, node: Element) -> None:
         self.protect_literal_text -= 1
-        if not node.get('is_multiline'):
+        if not node.get('is_multiline') or node.get('add_permalink'):
             self.add_permalink_ref(node, _('Permalink to this definition'))
         self.body.append('</dt>\n')