Implement meet for literal types; add tests for 'is_same_type' (#6043)

This pull request implements meets for literal types and adds some
corresponding tests.

It also adds a test suite for the `is_same_type` method while we're
at it. This test suite also lets you test each type's inherent
`__eq__` and `__hash__`, since we do also use those throughout the
code (especially for literal types).

mypy/meet.py

@@ -453,6 +453,8 @@ def visit_instance(self, t: Instance) -> Type:
             return meet_types(t, self.s)
         elif isinstance(self.s, TupleType):
             return meet_types(t, self.s)
+        elif isinstance(self.s, LiteralType):
+            return meet_types(t, self.s)
         return self.default(self.s)
 
     def visit_callable_type(self, t: CallableType) -> Type:
@@ -528,7 +530,12 @@ def visit_typeddict_type(self, t: TypedDictType) -> Type:
             return self.default(self.s)
 
     def visit_literal_type(self, t: LiteralType) -> Type:
-        raise NotImplementedError()
+        if isinstance(self.s, LiteralType) and self.s == t:
+            return t
+        elif isinstance(self.s, Instance) and is_subtype(t.fallback, self.s):
+            return t
+        else:
+            return self.default(self.s)
 
     def visit_partial_type(self, t: PartialType) -> Type:
         # We can't determine the meet of partial types. We should never get here.

mypy/test/testtypes.py

@@ -1,19 +1,21 @@
 """Test cases for mypy types and type operations."""
 
-from typing import List, Tuple
+from typing import List, Tuple, cast
 
 from mypy.test.helpers import Suite, assert_equal, assert_true, assert_false, assert_type, skip
 from mypy.erasetype import erase_type
 from mypy.expandtype import expand_type
 from mypy.join import join_types, join_simple
 from mypy.meet import meet_types
+from mypy.sametypes import is_same_type
 from mypy.types import (
     UnboundType, AnyType, CallableType, TupleType, TypeVarDef, Type, Instance, NoneTyp, Overloaded,
     TypeType, UnionType, UninhabitedType, true_only, false_only, TypeVarId, TypeOfAny, LiteralType
 )
 from mypy.nodes import ARG_POS, ARG_OPT, ARG_STAR, ARG_STAR2, CONTRAVARIANT, INVARIANT, COVARIANT
 from mypy.subtypes import is_subtype, is_more_precise, is_proper_subtype
 from mypy.test.typefixture import TypeFixture, InterfaceTypeFixture
+from mypy.experiments import strict_optional_set
 
 
 class TypesSuite(Suite):
@@ -846,8 +848,31 @@ def test_type_type(self) -> None:
         self.assert_meet(self.fx.type_type, self.fx.type_any, self.fx.type_any)
         self.assert_meet(self.fx.type_b, self.fx.anyt, self.fx.type_b)
 
+    def test_literal_type(self) -> None:
+        a = self.fx.a
+        d = self.fx.d
+        lit1 = LiteralType(1, a)
+        lit2 = LiteralType(2, a)
+        lit3 = LiteralType("foo", d)
+
+        self.assert_meet(lit1, lit1, lit1)
+        self.assert_meet(lit1, a, lit1)
+        self.assert_meet_uninhabited(lit1, lit3)
+        self.assert_meet_uninhabited(lit1, lit2)
+        self.assert_meet(UnionType([lit1, lit2]), lit1, lit1)
+        self.assert_meet(UnionType([lit1, lit2]), UnionType([lit2, lit3]), lit2)
+        self.assert_meet(UnionType([lit1, lit2]), UnionType([lit1, lit2]), UnionType([lit1, lit2]))
+        self.assert_meet(lit1, self.fx.anyt, lit1)
+        self.assert_meet(lit1, self.fx.o, lit1)
+
     # FIX generic interfaces + ranges
 
+    def assert_meet_uninhabited(self, s: Type, t: Type) -> None:
+        with strict_optional_set(False):
+            self.assert_meet(s, t, self.fx.nonet)
+        with strict_optional_set(True):
+            self.assert_meet(s, t, self.fx.uninhabited)
+
     def assert_meet(self, s: Type, t: Type, meet: Type) -> None:
         self.assert_simple_meet(s, t, meet)
         self.assert_simple_meet(t, s, meet)
@@ -874,3 +899,52 @@ def callable(self, *a: Type) -> CallableType:
         return CallableType(list(a[:-1]),
                             [ARG_POS] * n, [None] * n,
                             a[-1], self.fx.function)
+
+
+class SameTypeSuite(Suite):
+    def setUp(self) -> None:
+        self.fx = TypeFixture()
+
+    def test_literal_type(self) -> None:
+        a = self.fx.a
+        b = self.fx.b  # Reminder: b is a subclass of a
+        d = self.fx.d
+
+        # Literals are not allowed to contain floats, but we're going to
+        # test them anyways, just to make sure the semantics are robust
+        # against these kinds of things.
+        lit0 = LiteralType(cast(int, 1.0), a)
+        lit1 = LiteralType(1, b)
+        lit2 = LiteralType(2, b)
+        lit3 = LiteralType("foo", d)
+
+        self.assert_same(lit1, lit1)
+        self.assert_same(UnionType([lit1, lit2]), UnionType([lit1, lit2]))
+        self.assert_same(UnionType([lit1, lit2]), UnionType([lit2, lit1]))
+        self.assert_not_same(lit1, b)
+        self.assert_not_same(lit0, lit1)
+        self.assert_not_same(lit1, lit2)
+        self.assert_not_same(lit1, lit3)
+
+        self.assert_not_same(lit1, self.fx.anyt)
+        self.assert_not_same(lit1, self.fx.nonet)
+
+    def assert_same(self, s: Type, t: Type, strict: bool = True) -> None:
+        self.assert_simple_is_same(s, t, expected=True, strict=strict)
+        self.assert_simple_is_same(t, s, expected=True, strict=strict)
+
+    def assert_not_same(self, s: Type, t: Type, strict: bool = True) -> None:
+        self.assert_simple_is_same(s, t, False, strict=strict)
+        self.assert_simple_is_same(t, s, False, strict=strict)
+
+    def assert_simple_is_same(self, s: Type, t: Type, expected: bool, strict: bool) -> None:
+        actual = is_same_type(s, t)
+        assert_equal(actual, expected,
+                     'is_same_type({}, {}) is {{}} ({{}} expected)'.format(s, t))
+
+        if strict:
+            actual2 = (s == t)
+            assert_equal(actual2, expected,
+                         '({} == {}) is {{}} ({{}} expected)'.format(s, t))
+            assert_equal(hash(s) == hash(t), expected,
+                         '(hash({}) == hash({}) is {{}} ({{}} expected)'.format(s, t))

test-data/unit/check-literal.test

@@ -1240,3 +1240,73 @@ indirect.Literal()
 [builtins fixtures/isinstancelist.pyi]
 [out]
 
+
+--
+-- Other misc interactions
+--
+
+[case testLiteralMeets]
+from typing import TypeVar, List, Callable, Union
+from typing_extensions import Literal
+
+a: Callable[[Literal[1]], int]
+b: Callable[[Literal[2]], str]
+c: Callable[[int], str]
+d: Callable[[object], str]
+e: Callable[[Union[Literal[1], Literal[2]]], str]
+
+arr1 = [a, a]
+arr2 = [a, b]
+arr3 = [a, c]
+arr4 = [a, d]
+arr5 = [a, e]
+
+reveal_type(arr1)  # E: Revealed type is 'builtins.list[def (Literal[1]) -> builtins.int]'
+reveal_type(arr2)  # E: Revealed type is 'builtins.list[builtins.function*]'
+reveal_type(arr3)  # E: Revealed type is 'builtins.list[def (Literal[1]) -> builtins.object]'
+reveal_type(arr4)  # E: Revealed type is 'builtins.list[def (Literal[1]) -> builtins.object]'
+reveal_type(arr5)  # E: Revealed type is 'builtins.list[def (Literal[1]) -> builtins.object]'
+
+# Inspect just only one interesting one
+lit: Literal[1]
+reveal_type(arr2[0](lit))  # E: Revealed type is 'Any' \
+                           # E: Cannot call function of unknown type
+
+T = TypeVar('T')
+def unify(func: Callable[[T, T], None]) -> T: pass
+
+def f1(x: Literal[1], y: Literal[1]) -> None: pass
+def f2(x: Literal[1], y: Literal[2]) -> None: pass
+def f3(x: Literal[1], y: int) -> None: pass
+def f4(x: Literal[1], y: object) -> None: pass
+def f5(x: Literal[1], y: Union[Literal[1], Literal[2]]) -> None: pass
+
+reveal_type(unify(f1))  # E: Revealed type is 'Literal[1]'
+reveal_type(unify(f2))  # E: Revealed type is 'None'
+reveal_type(unify(f3))  # E: Revealed type is 'Literal[1]'
+reveal_type(unify(f4))  # E: Revealed type is 'Literal[1]'
+reveal_type(unify(f5))  # E: Revealed type is 'Literal[1]'
+[builtins fixtures/list.pyi]
+[out]
+
+[case testLiteralMeetsWithStrictOptional]
+# flags: --strict-optional
+from typing import TypeVar, Callable, Union
+from typing_extensions import Literal
+
+a: Callable[[Literal[1]], int]
+b: Callable[[Literal[2]], str]
+lit: Literal[1]
+
+arr = [a, b]
+reveal_type(arr)  # E: Revealed type is 'builtins.list[builtins.function*]'
+reveal_type(arr[0](lit))  # E: Revealed type is 'Any' \
+                          # E: Cannot call function of unknown type
+
+T = TypeVar('T')
+def unify(func: Callable[[T, T], None]) -> T: pass
+def func(x: Literal[1], y: Literal[2]) -> None: pass
+
+reveal_type(unify(func))  # E: Revealed type is '<nothing>'
+[builtins fixtures/list.pyi]
+[out]