1 files changed, 22 insertions, 13 deletions
diff --git a/sphinx/pycode/ast.py b/sphinx/pycode/ast.py
index d131ff4c1..db9bfefb3 100644
--- a/sphinx/pycode/ast.py
+++ b/sphinx/pycode/ast.py
@@ -9,7 +9,7 @@
 """
 
 import sys
-from typing import Dict, List, Optional, Type
+from typing import Dict, List, Optional, Type, overload
 
 if sys.version_info > (3, 8):
     import ast
@@ -58,6 +58,16 @@ def parse(code: str, mode: str = 'exec') -> "ast.AST":
         return ast.parse(code, mode=mode)
 
 
+@overload
+def unparse(node: None, code: str = '') -> None:
+    ...
+
+
+@overload
+def unparse(node: ast.AST, code: str = '') -> str:
+    ...
+
+
 def unparse(node: Optional[ast.AST], code: str = '') -> Optional[str]:
     """Unparse an AST to string."""
     if node is None:
@@ -146,6 +156,17 @@ class _UnparseVisitor(ast.NodeVisitor):
                 ["%s=%s" % (k.arg, self.visit(k.value)) for k in node.keywords])
         return "%s(%s)" % (self.visit(node.func), ", ".join(args))
 
+    def visit_Constant(self, node: ast.Constant) -> str:  # type: ignore
+        if node.value is Ellipsis:
+            return "..."
+        elif isinstance(node.value, (int, float, complex)):
+            if self.code and sys.version_info > (3, 8):
+                return ast.get_source_segment(self.code, node)  # type: ignore
+            else:
+                return repr(node.value)
+        else:
+            return repr(node.value)
+
     def visit_Dict(self, node: ast.Dict) -> str:
         keys = (self.visit(k) for k in node.keys)
         values = (self.visit(v) for v in node.values)
@@ -193,18 +214,6 @@ class _UnparseVisitor(ast.NodeVisitor):
         else:
             return "()"
 
-    if sys.version_info >= (3, 6):
-        def visit_Constant(self, node: ast.Constant) -> str:
-            if node.value is Ellipsis:
-                return "..."
-            elif isinstance(node.value, (int, float, complex)):
-                if self.code and sys.version_info > (3, 8):
-                    return ast.get_source_segment(self.code, node)
-                else:
-                    return repr(node.value)
-            else:
-                return repr(node.value)
-
     if sys.version_info < (3, 8):
         # these ast nodes were deprecated in python 3.8
         def visit_Bytes(self, node: ast.Bytes) -> str: