stubtest: if a default is present in the stub, check that it is correct

Helps with python/typeshed#8988.

mypy/stubtest.py

@@ -7,6 +7,7 @@
 from __future__ import annotations
 
 import argparse
+import ast
 import collections.abc
 import copy
 import enum
@@ -29,13 +30,15 @@
 
 import mypy.build
 import mypy.modulefinder
+import mypy.nodes
 import mypy.state
 import mypy.types
 import mypy.version
 from mypy import nodes
 from mypy.config_parser import parse_config_file
 from mypy.options import Options
 from mypy.util import FancyFormatter, bytes_to_human_readable_repr, is_dunder, plural_s
+from mypy.visitor import ExpressionVisitor
 
 
 class Missing:
@@ -540,6 +543,179 @@ def names_approx_match(a: str, b: str) -> bool:
     )
 
 
+class _NodeEvaluator(ExpressionVisitor[object]):
+    def visit_int_expr(self, o: mypy.nodes.IntExpr) -> int:
+        return o.value
+
+    def visit_str_expr(self, o: mypy.nodes.StrExpr) -> str:
+        return o.value
+
+    def visit_bytes_expr(self, o: mypy.nodes.BytesExpr) -> bytes:
+        try:
+            return ast.literal_eval(f"b'{o.value}'")
+        except SyntaxError:
+            return ast.literal_eval(f'b"{o.value}"')
+
+    def visit_float_expr(self, o: mypy.nodes.FloatExpr) -> float:
+        return o.value
+
+    def visit_complex_expr(self, o: mypy.nodes.ComplexExpr) -> object:
+        return o.value
+
+    def visit_ellipsis(self, o: mypy.nodes.EllipsisExpr) -> object:
+        return Ellipsis
+
+    def visit_star_expr(self, o: mypy.nodes.StarExpr) -> object:
+        return MISSING
+
+    def visit_name_expr(self, o: mypy.nodes.NameExpr) -> object:
+        if o.name == "True":
+            return True
+        elif o.name == "False":
+            return False
+        elif o.name == "None":
+            return None
+        return MISSING
+
+    def visit_member_expr(self, o: mypy.nodes.MemberExpr) -> object:
+        return MISSING
+
+    def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr) -> object:
+        return MISSING
+
+    def visit_yield_expr(self, o: mypy.nodes.YieldExpr) -> object:
+        return MISSING
+
+    def visit_call_expr(self, o: mypy.nodes.CallExpr) -> object:
+        return MISSING
+
+    def visit_op_expr(self, o: mypy.nodes.OpExpr) -> object:
+        return MISSING
+
+    def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr) -> object:
+        return MISSING
+
+    def visit_cast_expr(self, o: mypy.nodes.CastExpr) -> object:
+        return o.expr.accept(self)
+
+    def visit_assert_type_expr(self, o: mypy.nodes.AssertTypeExpr) -> object:
+        return o.expr.accept(self)
+
+    def visit_reveal_expr(self, o: mypy.nodes.RevealExpr) -> object:
+        return MISSING
+
+    def visit_super_expr(self, o: mypy.nodes.SuperExpr) -> object:
+        return MISSING
+
+    def visit_unary_expr(self, o: mypy.nodes.UnaryExpr) -> object:
+        operand = o.expr.accept(self)
+        if operand is MISSING:
+            return MISSING
+        if o.op == "-":
+            if isinstance(operand, (int, float, complex)):
+                return -operand
+        elif o.op == "+":
+            if isinstance(operand, (int, float, complex)):
+                return +operand
+        elif o.op == "~":
+            if isinstance(operand, int):
+                return ~operand
+        elif o.op == "not":
+            if isinstance(operand, (bool, int, float, str, bytes)):
+                return not operand
+        return MISSING
+
+    def visit_assignment_expr(self, o: mypy.nodes.AssignmentExpr) -> object:
+        return o.value.accept(self)
+
+    def visit_list_expr(self, o: mypy.nodes.ListExpr) -> object:
+        items = [item.accept(self) for item in o.items]
+        if all(item is not MISSING for item in items):
+            return items
+        return MISSING
+
+    def visit_dict_expr(self, o: mypy.nodes.DictExpr) -> object:
+        items = [
+            (MISSING if key is None else key.accept(self), value.accept(self))
+            for key, value in o.items
+        ]
+        if all(key is not MISSING and value is not None for key, value in items):
+            return dict(items)
+        return MISSING
+
+    def visit_tuple_expr(self, o: mypy.nodes.TupleExpr) -> object:
+        items = [item.accept(self) for item in o.items]
+        if all(item is not MISSING for item in items):
+            return tuple(items)
+        return MISSING
+
+    def visit_set_expr(self, o: mypy.nodes.SetExpr) -> object:
+        items = [item.accept(self) for item in o.items]
+        if all(item is not MISSING for item in items):
+            return set(items)
+        return MISSING
+
+    def visit_index_expr(self, o: mypy.nodes.IndexExpr) -> object:
+        return MISSING
+
+    def visit_type_application(self, o: mypy.nodes.TypeApplication) -> object:
+        return MISSING
+
+    def visit_lambda_expr(self, o: mypy.nodes.LambdaExpr) -> object:
+        return MISSING
+
+    def visit_list_comprehension(self, o: mypy.nodes.ListComprehension) -> object:
+        return MISSING
+
+    def visit_set_comprehension(self, o: mypy.nodes.SetComprehension) -> object:
+        return MISSING
+
+    def visit_dictionary_comprehension(self, o: mypy.nodes.DictionaryComprehension) -> object:
+        return MISSING
+
+    def visit_generator_expr(self, o: mypy.nodes.GeneratorExpr) -> object:
+        return MISSING
+
+    def visit_slice_expr(self, o: mypy.nodes.SliceExpr) -> object:
+        return MISSING
+
+    def visit_conditional_expr(self, o: mypy.nodes.ConditionalExpr) -> object:
+        return MISSING
+
+    def visit_type_var_expr(self, o: mypy.nodes.TypeVarExpr) -> object:
+        return MISSING
+
+    def visit_paramspec_expr(self, o: mypy.nodes.ParamSpecExpr) -> object:
+        return MISSING
+
+    def visit_type_var_tuple_expr(self, o: mypy.nodes.TypeVarTupleExpr) -> object:
+        return MISSING
+
+    def visit_type_alias_expr(self, o: mypy.nodes.TypeAliasExpr) -> object:
+        return MISSING
+
+    def visit_namedtuple_expr(self, o: mypy.nodes.NamedTupleExpr) -> object:
+        return MISSING
+
+    def visit_enum_call_expr(self, o: mypy.nodes.EnumCallExpr) -> object:
+        return MISSING
+
+    def visit_typeddict_expr(self, o: mypy.nodes.TypedDictExpr) -> object:
+        return MISSING
+
+    def visit_newtype_expr(self, o: mypy.nodes.NewTypeExpr) -> object:
+        return MISSING
+
+    def visit__promote_expr(self, o: mypy.nodes.PromoteExpr) -> object:
+        return MISSING
+
+    def visit_await_expr(self, o: mypy.nodes.AwaitExpr) -> object:
+        return MISSING
+
+    def visit_temp_node(self, o: mypy.nodes.TempNode) -> object:
+        return MISSING
+
+
 def _verify_arg_default_value(
     stub_arg: nodes.Argument, runtime_arg: inspect.Parameter
 ) -> Iterator[str]:
@@ -573,6 +749,21 @@ def _verify_arg_default_value(
                     f"has a default value of type {runtime_type}, "
                     f"which is incompatible with stub argument type {stub_type}"
                 )
+            if runtime_arg.default is not ... and stub_arg.initializer is not None:
+                stub_default = stub_arg.initializer.accept(_NodeEvaluator())
+                if (
+                    stub_default is not MISSING
+                    and stub_default is not ...
+                    and (
+                        stub_default != runtime_arg.default
+                        or type(stub_default) is not type(runtime_arg.default)
+                    )
+                ):
+                    yield (
+                        f'runtime argument "{runtime_arg.name}" '
+                        f"has a default value of {runtime_arg.default!r}, "
+                        f"which is different from stub argument default {stub_default!r}"
+                    )
     else:
         if stub_arg.kind.is_optional():
             yield (

mypy/test/teststubtest.py

@@ -302,7 +302,7 @@ def test_arg_kind(self) -> Iterator[Case]:
             )
 
     @collect_cases
-    def test_default_value(self) -> Iterator[Case]:
+    def test_default_presence(self) -> Iterator[Case]:
         yield Case(
             stub="def f1(text: str = ...) -> None: ...",
             runtime="def f1(text = 'asdf'): pass",
@@ -336,6 +336,59 @@ def f6(text: _T = ...) -> None: ...
             error="f6",
         )
 
+    @collect_cases
+    def test_default_value(self) -> Iterator[Case]:
+        yield Case(
+            stub="def f1(text: str = 'x') -> None: ...",
+            runtime="def f1(text = 'y'): pass",
+            error="f1",
+        )
+        yield Case(
+            stub='def f2(text: bytes = b"x\'") -> None: ...',
+            runtime='def f2(text = b"x\'"): pass',
+            error=None,
+        )
+        yield Case(
+            stub='def f3(text: bytes = b"y\'") -> None: ...',
+            runtime='def f3(text = b"x\'"): pass',
+            error="f3",
+        )
+        yield Case(
+            stub="def f4(text: object = 1) -> None: ...",
+            runtime="def f4(text = 1.0): pass",
+            error="f4",
+        )
+        yield Case(
+            stub="def f5(text: object = True) -> None: ...",
+            runtime="def f5(text = 1): pass",
+            error="f5",
+        )
+        yield Case(
+            stub="def f6(text: object = True) -> None: ...",
+            runtime="def f6(text = True): pass",
+            error=None,
+        )
+        yield Case(
+            stub="def f7(text: object = not True) -> None: ...",
+            runtime="def f7(text = False): pass",
+            error=None,
+        )
+        yield Case(
+            stub="def f8(text: object = not True) -> None: ...",
+            runtime="def f8(text = True): pass",
+            error="f8",
+        )
+        yield Case(
+            stub="def f9(text: object = {1: 2}) -> None: ...",
+            runtime="def f9(text = {1: 3}): pass",
+            error="f9",
+        )
+        yield Case(
+            stub="def f10(text: object = [1, 2]) -> None: ...",
+            runtime="def f10(text = [1, 2]): pass",
+            error=None,
+        )
+
     @collect_cases
     def test_static_class_method(self) -> Iterator[Case]:
         yield Case(