transformer: support unary literals

basedtyping/transformer.py

@@ -107,7 +107,9 @@ def _basedtyping(self, attr: str) -> ast.Attribute:
         )
         return ast.fix_missing_locations(result)
 
-    def _literal(self, value: ast.Constant | ast.Name | ast.Attribute) -> ast.Subscript:
+    def _literal(
+        self, value: ast.Constant | ast.Name | ast.Attribute | ast.UnaryOp
+    ) -> ast.Subscript:
         return self.subscript(self._typing("Literal"), value)
 
     def subscript(self, value: ast.expr, slice_: ast.expr) -> ast.Subscript:
@@ -178,6 +180,14 @@ def visit_Constant(self, node: ast.Constant) -> ast.AST:
             return self._literal(node)
         return node
 
+    @override
+    def visit_UnaryOp(self, node: ast.UnaryOp) -> ast.AST:
+        if not isinstance(node.operand, ast.Constant):
+            return node
+        if not isinstance(node.op, (ast.UAdd, ast.USub)):
+            return node
+        return self._literal(node)
+
     @override
     def visit_Tuple(self, node: ast.Tuple) -> ast.AST:
         with self.implicit_tuple(value=False):

tests/test_transformer.py

@@ -31,6 +31,11 @@ def test_literal():
     validate("1 | 2", Union[Literal[1], Literal[2]])
 
 
+def test_negative():
+    validate("-1", Literal[-1])
+    validate("+1", Literal[1])
+
+
 def test_literal_union():
     validate("Union[1, 2]", Union[Literal[1], Literal[2]])