more enum-related speedups (#12032)

As a followup to #9394 address a few more O(n**2) behaviors
caused by decomposing enums into unions of literals.

mypy/meet.py

@@ -64,6 +64,8 @@ def narrow_declared_type(declared: Type, narrowed: Type) -> Type:
     if isinstance(declared, UnionType):
         return make_simplified_union([narrow_declared_type(x, narrowed)
                                       for x in declared.relevant_items()])
+    if is_enum_overlapping_union(declared, narrowed):
+        return narrowed
     elif not is_overlapping_types(declared, narrowed,
                                   prohibit_none_typevar_overlap=True):
         if state.strict_optional:
@@ -137,6 +139,22 @@ def get_possible_variants(typ: Type) -> List[Type]:
         return [typ]
 
 
+def is_enum_overlapping_union(x: ProperType, y: ProperType) -> bool:
+    """Return True if x is an Enum, and y is an Union with at least one Literal from x"""
+    return (
+        isinstance(x, Instance) and x.type.is_enum and
+        isinstance(y, UnionType) and
+        any(isinstance(p, LiteralType) and x.type == p.fallback.type
+            for p in (get_proper_type(z) for z in y.relevant_items()))
+    )
+
+
+def is_literal_in_union(x: ProperType, y: ProperType) -> bool:
+    """Return True if x is a Literal and y is an Union that includes x"""
+    return (isinstance(x, LiteralType) and isinstance(y, UnionType) and
+            any(x == get_proper_type(z) for z in y.items))
+
+
 def is_overlapping_types(left: Type,
                          right: Type,
                          ignore_promotions: bool = False,
@@ -198,6 +216,18 @@ def _is_overlapping_types(left: Type, right: Type) -> bool:
     #
     # These checks will also handle the NoneType and UninhabitedType cases for us.
 
+    # enums are sometimes expanded into an Union of Literals
+    # when that happens we want to make sure we treat the two as overlapping
+    # and crucially, we want to do that *fast* in case the enum is large
+    # so we do it before expanding variants below to avoid O(n**2) behavior
+    if (
+        is_enum_overlapping_union(left, right)
+        or is_enum_overlapping_union(right, left)
+        or is_literal_in_union(left, right)
+        or is_literal_in_union(right, left)
+    ):
+        return True
+
     if (is_proper_subtype(left, right, ignore_promotions=ignore_promotions)
             or is_proper_subtype(right, left, ignore_promotions=ignore_promotions)):
         return True

mypy/sametypes.py

@@ -1,12 +1,12 @@
-from typing import Sequence
+from typing import Sequence, Tuple, Set, List
 
 from mypy.types import (
     Type, UnboundType, AnyType, NoneType, TupleType, TypedDictType,
     UnionType, CallableType, TypeVarType, Instance, TypeVisitor, ErasedType,
     Overloaded, PartialType, DeletedType, UninhabitedType, TypeType, LiteralType,
     ProperType, get_proper_type, TypeAliasType, ParamSpecType, Parameters, UnpackType
 )
-from mypy.typeops import tuple_fallback, make_simplified_union
+from mypy.typeops import tuple_fallback, make_simplified_union, is_simple_literal
 
 
 def is_same_type(left: Type, right: Type) -> bool:
@@ -49,6 +49,22 @@ def is_same_types(a1: Sequence[Type], a2: Sequence[Type]) -> bool:
     return True
 
 
+def _extract_literals(u: UnionType) -> Tuple[Set[Type], List[Type]]:
+    """Given a UnionType, separate out its items into a set of simple literals and a remainder list
+    This is a useful helper to avoid O(n**2) behavior when comparing large unions, which can often
+    result from large enums in contexts where type narrowing removes a small subset of entries.
+    """
+    lit: Set[Type] = set()
+    rem: List[Type] = []
+    for i in u.relevant_items():
+        i = get_proper_type(i)
+        if is_simple_literal(i):
+            lit.add(i)
+        else:
+            rem.append(i)
+    return lit, rem
+
+
 class SameTypeVisitor(TypeVisitor[bool]):
     """Visitor for checking whether two types are the 'same' type."""
 
@@ -153,14 +169,20 @@ def visit_literal_type(self, left: LiteralType) -> bool:
 
     def visit_union_type(self, left: UnionType) -> bool:
         if isinstance(self.right, UnionType):
+            left_lit, left_rem = _extract_literals(left)
+            right_lit, right_rem = _extract_literals(self.right)
+
+            if left_lit != right_lit:
+                return False
+
             # Check that everything in left is in right
-            for left_item in left.items:
-                if not any(is_same_type(left_item, right_item) for right_item in self.right.items):
+            for left_item in left_rem:
+                if not any(is_same_type(left_item, right_item) for right_item in right_rem):
                     return False
 
             # Check that everything in right is in left
-            for right_item in self.right.items:
-                if not any(is_same_type(right_item, left_item) for left_item in left.items):
+            for right_item in right_rem:
+                if not any(is_same_type(right_item, left_item) for left_item in left_rem):
                     return False
 
             return True

mypy/subtypes.py

@@ -535,6 +535,20 @@ def visit_overloaded(self, left: Overloaded) -> bool:
             return False
 
     def visit_union_type(self, left: UnionType) -> bool:
+        if isinstance(self.right, Instance):
+            literal_types: Set[Instance] = set()
+            # avoid redundant check for union of literals
+            for item in left.relevant_items():
+                item = get_proper_type(item)
+                lit_type = mypy.typeops.simple_literal_type(item)
+                if lit_type is not None:
+                    if lit_type in literal_types:
+                        continue
+                    literal_types.add(lit_type)
+                    item = lit_type
+                if not self._is_subtype(item, self.orig_right):
+                    return False
+            return True
         return all(self._is_subtype(item, self.orig_right) for item in left.items)
 
     def visit_partial_type(self, left: PartialType) -> bool:
@@ -1199,6 +1213,27 @@ def report(*args: Any) -> None:
     return applied
 
 
+def try_restrict_literal_union(t: UnionType, s: Type) -> Optional[List[Type]]:
+    """Return the items of t, excluding any occurrence of s, if and only if
+      - t only contains simple literals
+      - s is a simple literal
+
+    Otherwise, returns None
+    """
+    ps = get_proper_type(s)
+    if not mypy.typeops.is_simple_literal(ps):
+        return None
+
+    new_items: List[Type] = []
+    for i in t.relevant_items():
+        pi = get_proper_type(i)
+        if not mypy.typeops.is_simple_literal(pi):
+            return None
+        if pi != ps:
+            new_items.append(i)
+    return new_items
+
+
 def restrict_subtype_away(t: Type, s: Type, *, ignore_promotions: bool = False) -> Type:
     """Return t minus s for runtime type assertions.
 
@@ -1212,10 +1247,14 @@ def restrict_subtype_away(t: Type, s: Type, *, ignore_promotions: bool = False)
     s = get_proper_type(s)
 
     if isinstance(t, UnionType):
-        new_items = [restrict_subtype_away(item, s, ignore_promotions=ignore_promotions)
-                     for item in t.relevant_items()
-                     if (isinstance(get_proper_type(item), AnyType) or
-                         not covers_at_runtime(item, s, ignore_promotions))]
+        new_items = try_restrict_literal_union(t, s)
+        if new_items is None:
+            new_items = [
+                restrict_subtype_away(item, s, ignore_promotions=ignore_promotions)
+                for item in t.relevant_items()
+                if (isinstance(get_proper_type(item), AnyType) or
+                    not covers_at_runtime(item, s, ignore_promotions))
+            ]
         return UnionType.make_union(new_items)
     elif covers_at_runtime(t, s, ignore_promotions):
         return UninhabitedType()
@@ -1285,11 +1324,11 @@ def _is_proper_subtype(left: Type, right: Type, *,
     right = get_proper_type(right)
 
     if isinstance(right, UnionType) and not isinstance(left, UnionType):
-        return any([is_proper_subtype(orig_left, item,
-                                      ignore_promotions=ignore_promotions,
-                                      erase_instances=erase_instances,
-                                      keep_erased_types=keep_erased_types)
-                    for item in right.items])
+        return any(is_proper_subtype(orig_left, item,
+                                     ignore_promotions=ignore_promotions,
+                                     erase_instances=erase_instances,
+                                     keep_erased_types=keep_erased_types)
+                   for item in right.items)
     return left.accept(ProperSubtypeVisitor(orig_right,
                                             ignore_promotions=ignore_promotions,
                                             erase_instances=erase_instances,
@@ -1495,7 +1534,7 @@ def visit_overloaded(self, left: Overloaded) -> bool:
         return False
 
     def visit_union_type(self, left: UnionType) -> bool:
-        return all([self._is_proper_subtype(item, self.orig_right) for item in left.items])
+        return all(self._is_proper_subtype(item, self.orig_right) for item in left.items)
 
     def visit_partial_type(self, left: PartialType) -> bool:
         # TODO: What's the right thing to do here?

mypy/typeops.py

@@ -318,6 +318,15 @@ def simple_literal_value_key(t: ProperType) -> Optional[Tuple[str, ...]]:
     return None
 
 
+def simple_literal_type(t: ProperType) -> Optional[Instance]:
+    """Extract the underlying fallback Instance type for a simple Literal"""
+    if isinstance(t, Instance) and t.last_known_value is not None:
+        t = t.last_known_value
+    if isinstance(t, LiteralType):
+        return t.fallback
+    return None
+
+
 def is_simple_literal(t: ProperType) -> bool:
     """Fast way to check if simple_literal_value_key() would return a non-None value."""
     if isinstance(t, LiteralType):