Add conformance test for generic types as base classes (#1590)

Author: hauntsaninja

conformance/results/mypy/generics_base_class.toml

@@ -0,0 +1,6 @@
+conformant = "Pass"
+output = """
+generics_base_class.py:22: error: Argument 1 to "takes_dict_incorrect" has incompatible type "SymbolTable"; expected "dict[str, list[object]]"  [arg-type]
+generics_base_class.py:37: error: "LinkedList" expects 1 type argument, but 2 given  [type-arg]
+generics_base_class.py:46: error: "MyDict" expects 1 type argument, but 2 given  [type-arg]
+"""

conformance/results/pyre/generics_base_class.toml

@@ -0,0 +1,10 @@
+conformant = "Pass"
+notes = """
+Doesn't allow using generic in assert_type expression.
+"""
+output = """
+generics_base_class.py:22:25 Incompatible parameter type [6]: In call `takes_dict_incorrect`, for 1st positional argument, expected `Dict[str, List[object]]` but got `SymbolTable`.
+generics_base_class.py:34:25 Undefined attribute [16]: `typing.Iterator` has no attribute `__getitem__`.
+generics_base_class.py:37:21 Invalid type parameters [24]: Generic type `LinkedList` expects 1 type parameter, received 2.
+generics_base_class.py:46:17 Invalid type parameters [24]: Generic type `MyDict` expects 1 type parameter, received 2.
+"""

conformance/results/pyright/generics_base_class.toml

@@ -0,0 +1,9 @@
+conformant = "Pass"
+output = """
+generics_base_class.py:22:26 - error: Argument of type "SymbolTable" cannot be assigned to parameter "x" of type "dict[str, list[object]]" in function "takes_dict_incorrect"
+  "SymbolTable" is incompatible with "dict[str, list[object]]"
+    Type parameter "_VT@dict" is invariant, but "list[Node]" is not the same as "list[object]"
+    Consider switching from "dict" to "Mapping" which is covariant in the value type (reportGeneralTypeIssues)
+generics_base_class.py:37:38 - error: Too many type arguments provided for "LinkedList"; expected 1 but received 2 (reportGeneralTypeIssues)
+generics_base_class.py:46:30 - error: Too many type arguments provided for "MyDict"; expected 1 but received 2 (reportGeneralTypeIssues)
+"""

conformance/results/pytype/generics_base_class.toml

@@ -0,0 +1,10 @@
+conformant = "Partial"
+notes = """
+False negative on passing SymbolTable to dict[str, list[object]].
+"""
+output = """
+File "generics_base_class.py", line 37, in <module>: Invalid type annotation 'LinkedList[int, int]'  [invalid-annotation]
+  LinkedList[T] expected 1 parameter, got 2
+File "generics_base_class.py", line 46, in <module>: Invalid type annotation 'MyDict[int, int]'  [invalid-annotation]
+  MyDict[T] expected 1 parameter, got 2
+"""

conformance/tests/generics_base_class.py

@@ -0,0 +1,46 @@
+# Specification: https://typing.readthedocs.io/en/latest/spec/generics.html#arbitrary-generic-types-as-base-classes
+
+from typing import TypeVar, Iterable, assert_type
+
+T = TypeVar("T")
+
+# > Generic[T] is only valid as a base class – it’s not a proper type. However,
+# > user-defined generic types [...] and built-in generic types and ABCs such as
+# > list[T] and Iterable[T] are valid both as types and as base classes.
+
+class Node: ...
+
+class SymbolTable(dict[str, list[Node]]): ...
+
+def takes_dict(x: dict): ...
+def takes_dict_typed(x: dict[str, list[Node]]): ...
+def takes_dict_incorrect(x: dict[str, list[object]]): ...
+
+def test_symbol_table(s: SymbolTable):
+    takes_dict(s)  # OK
+    takes_dict_typed(s)  # OK
+    takes_dict_incorrect(s)  # Type error
+
+# > If a generic base class has a type variable as a type argument, this makes
+# > the defined class generic.
+
+# Note that there is overlap in the spec and tests in generics_basic.py
+
+from collections.abc import Iterable, Container, Iterator
+
+class LinkedList(Iterable[T], Container[T]): ...
+
+def test_linked_list(l: LinkedList[int]):
+    assert_type(iter(l), Iterator[int])
+    assert_type(l.__contains__(1), bool)
+
+linked_list_invalid: LinkedList[int, int]  # Type error
+
+from collections.abc import Mapping
+
+class MyDict(Mapping[str, T]): ...
+
+def test_my_dict(d: MyDict[int]):
+    assert_type(d["a"], int)
+
+my_dict_invalid: MyDict[int, int]  # Type error