Add regression tests for builtins.pow and object.__reduce__ (#7663)

Author: AlexWaygood

pyrightconfig.json

@@ -2,7 +2,8 @@
     "typeshedPath": ".",
     "include": [
         "stdlib",
-        "stubs"
+        "stubs",
+        "test_cases"
     ],
     "exclude": [
         "**/@python2"

pyrightconfig.stricter.json

@@ -3,7 +3,8 @@
     "typeshedPath": ".",
     "include": [
         "stdlib",
-        "stubs"
+        "stubs",
+        "test_cases"
     ],
     "exclude": [
         "**/@python2",

test_cases/README.md

@@ -0,0 +1,24 @@
+## Regression tests for typeshed
+
+This directory contains regression tests for the stubs found elsewhere in the
+typeshed repo. Each file contains a number of test cases, all of which should
+pass a type checker without error.
+
+**This directory should *only* contain tests for functions and classes which
+are known to have caused problems in the past, where the stubs are difficult to
+get right.** 100% test coverage for typeshed is neither necessary nor
+desirable, as it would lead to code duplication. Moreover, typeshed has
+multiple other mechanisms for spotting errors in the stubs.
+
+Unlike the rest of typeshed, this directory largely contains `.py` files. This
+is because the purpose of this folder is to test the implications of typeshed
+changes for end users.
+
+Another difference to the rest of typeshed is that the test cases in this
+directory cannot always use modern syntax for type hints. For example, PEP 604
+syntax (unions with a pipe `|` operator) is new in Python 3.10. While this
+syntax can be used on older Python versions in a `.pyi` file, code using this
+syntax will fail at runtime on Python <=3.9. Since the test cases all use `.py`
+extensions, and since the tests need to pass on all Python versions >=3.6, PEP
+604 syntax cannot be used in a test case. Use `typing.Union` and
+`typing.Optional` instead.

test_cases/stdlib/builtins/test_object.py

@@ -0,0 +1,11 @@
+from typing import Any, Tuple, Union
+
+
+# The following should pass without error (see #6661):
+class Diagnostic:
+    def __reduce__(self) -> Union[str, Tuple[Any, ...]]:
+        res = super().__reduce__()
+        if isinstance(res, tuple) and len(res) >= 3:
+            res[2]["_info"] = 42
+
+        return res

test_cases/stdlib/builtins/test_pow.py

@@ -0,0 +1,40 @@
+from decimal import Decimal
+from fractions import Fraction
+from typing import Any, NoReturn
+from typing_extensions import Literal, assert_type
+
+assert_type(pow(1, 0), Literal[1])  # See #7163
+assert_type(pow(1, 0, None), Literal[1])  # See #7163
+assert_type(pow(2, 4, 0), NoReturn)
+assert_type(pow(2, 4), int)
+assert_type(pow(4, 6, None), int)
+assert_type(pow(5, -7), float)
+assert_type(pow(2, 4, 5), int)  # pow(<smallint>, <smallint>, <smallint>)
+assert_type(pow(2, 35, 3), int)  # pow(<smallint>, <bigint>, <smallint>)
+assert_type(pow(4.6, 8), float)
+assert_type(pow(5.1, 4, None), float)
+assert_type(pow(complex(6), 6.2), complex)
+assert_type(pow(complex(9), 7.3, None), complex)
+assert_type(pow(Fraction(), 4, None), Fraction)
+assert_type(pow(Fraction(3, 7), complex(1, 8)), complex)
+assert_type(pow(complex(4, -8), Fraction(2, 3)), complex)
+assert_type(pow(Decimal("1.0"), Decimal("1.6")), Decimal)
+assert_type(pow(Decimal("1.0"), Decimal("1.0"), Decimal("1.0")), Decimal)
+assert_type(pow(Decimal("4.6"), 7, None), Decimal)
+
+# These would ideally be more precise, but `Any` is acceptable
+# They have to be `Any` due to the fact that type-checkers can't distinguish between positive and negative numbers for the second argument to `pow()`
+#
+# int for positive 2nd-arg, float otherwise
+assert_type(pow(4, 65), Any)
+assert_type(pow(2, -45), Any)
+assert_type(pow(3, 57, None), Any)
+# pow(<pos-float>, <pos-or-neg-float>) -> float
+# pow(<neg-float>, <pos-or-neg-float>) -> complex
+assert_type(pow(4.7, 7.4), Any)
+assert_type(pow(-9.8, 8.3), Any)
+assert_type(pow(-9.3, -88.2), Any)
+assert_type(pow(8.2, -9.8), Any)
+assert_type(pow(4.7, 9.2, None), Any)
+# See #7046 -- float for a positive 1st arg, complex otherwise
+assert_type((-2) ** 0.5, Any)