Use both sides of type context for generic type inference (part 1)

mypy/checkexpr.py

@@ -19,6 +19,7 @@
 from mypy.checkmember import analyze_member_access, has_operator
 from mypy.checkstrformat import StringFormatterChecker
 from mypy.constant_fold import constant_fold_expr
+from mypy.constraints import Constraint
 from mypy.erasetype import erase_type, remove_instance_last_known_values, replace_meta_vars
 from mypy.errors import ErrorInfo, ErrorWatcher, report_internal_error
 from mypy.expandtype import (
@@ -1792,8 +1793,10 @@ def check_callable_call(
                     callee = freshen_function_type_vars(callee)
                 self.freshen_cache[(context, original_callee)] = callee
 
+        initial_callee = callee
+        constraints: list[Constraint] = []
         if callee.is_generic():
-            callee = self.infer_function_type_arguments_using_context(callee, context)
+            callee, constraints = self.infer_function_type_arguments_using_context(callee, context)
 
         formal_to_actual = map_actuals_to_formals(
             arg_kinds,
@@ -1825,12 +1828,20 @@ def check_callable_call(
                     )
                     callee = callee.copy_modified(arg_types=[new_arg_type])
 
-        if callee.is_generic():
+        if initial_callee.is_generic():
             need_refresh = any(
-                isinstance(v, (ParamSpecType, TypeVarTupleType)) for v in callee.variables
+                isinstance(v, (ParamSpecType, TypeVarTupleType)) for v in initial_callee.variables
             )
             callee = self.infer_function_type_arguments(
-                callee, args, arg_kinds, arg_names, formal_to_actual, need_refresh, context
+                callee,
+                initial_callee,
+                constraints,
+                args,
+                arg_kinds,
+                arg_names,
+                formal_to_actual,
+                need_refresh,
+                context,
             )
             if need_refresh:
                 # Argument kinds etc. may have changed due to
@@ -2113,7 +2124,7 @@ def infer_arg_types_in_context(
 
     def infer_function_type_arguments_using_context(
         self, callable: CallableType, error_context: Context
-    ) -> CallableType:
+    ) -> tuple[CallableType, list[Constraint]]:
         """Unify callable return type to type context to infer type vars.
 
         For example, if the return type is set[t] where 't' is a type variable
@@ -2122,7 +2133,7 @@ def infer_function_type_arguments_using_context(
         """
         ctx = self.type_context[-1]
         if not ctx:
-            return callable
+            return callable, []
         # The return type may have references to type metavariables that
         # we are inferring right now. We must consider them as indeterminate
         # and they are not potential results; thus we replace them with the
@@ -2179,8 +2190,8 @@ def infer_function_type_arguments_using_context(
             # TODO: we may want to add similar exception if all arguments are lambdas, since
             # in this case external context is almost everything we have.
             if not is_generic_instance(ctx) and not is_literal_type_like(ctx):
-                return callable.copy_modified()
-        args = infer_type_arguments(
+                return callable.copy_modified(), []
+        args, constraints = infer_type_arguments(
             callable.variables, ret_type, erased_ctx, skip_unsatisfied=True
         )
         # Only substitute non-Uninhabited and non-erased types.
@@ -2192,13 +2203,16 @@ def infer_function_type_arguments_using_context(
                 new_args.append(arg)
         # Don't show errors after we have only used the outer context for inference.
         # We will use argument context to infer more variables.
-        return self.apply_generic_arguments(
-            callable, new_args, error_context, skip_unsatisfied=True
+        return (
+            self.apply_generic_arguments(callable, new_args, error_context, skip_unsatisfied=True),
+            constraints,
         )
 
     def infer_function_type_arguments(
         self,
         callee_type: CallableType,
+        initial_callee_type: CallableType,
+        ret_constraints: list[Constraint],
         args: list[Expression],
         arg_kinds: list[ArgKind],
         arg_names: Sequence[str | None] | None,
@@ -2208,7 +2222,8 @@ def infer_function_type_arguments(
     ) -> CallableType:
         """Infer the type arguments for a generic callee type.
 
-        Infer based on the types of arguments.
+        Infer based on the types of arguments. The `initial_callee_type` is callee
+        type before applying arguments inferred from return type context.
 
         Return a derived callable type that has the arguments applied.
         """
@@ -2233,6 +2248,44 @@ def infer_function_type_arguments(
                 else:
                     pass1_args.append(arg)
 
+            # First, try inferring callee type using both argument type and return
+            # constraints. Do not do this if special_sig is set or for type objects,
+            # those are special-cased elsewhere.
+            if (
+                initial_callee_type != callee_type
+                and initial_callee_type.special_sig is None
+                and not initial_callee_type.is_type_obj()
+                # This is not very principled, but also prefer outer context for
+                # recursive types (because values can never be recursive).
+                and not type_state.infer_unions
+            ):
+                inferred_args, _ = infer_function_type_arguments(
+                    initial_callee_type,
+                    pass1_args,
+                    arg_kinds,
+                    arg_names,
+                    formal_to_actual,
+                    context=self.argument_infer_context(),
+                    strict=self.chk.in_checked_function(),
+                    extra_constraints=ret_constraints,
+                )
+                # Only use two-side inference if it is fully successful,
+                # otherwise, fallback to return type context as a tiebreaker.
+                if not any(
+                    a is None
+                    or isinstance(get_proper_type(a), UninhabitedType)
+                    or has_erased_component(a)
+                    or set(get_type_vars(a)) & set(callee_type.variables)
+                    for a in inferred_args
+                ):
+                    return self.apply_inferred_arguments(
+                        initial_callee_type, inferred_args, context
+                    )
+
+            if not callee_type.is_generic():
+                # Fast path: return context inferred all type arguments.
+                return callee_type
+
             inferred_args, _ = infer_function_type_arguments(
                 callee_type,
                 pass1_args,
@@ -6281,7 +6334,12 @@ def accept(
             # context, and use enclosing one, see infer_lambda_type_using_context().
             # TODO: consider using cache for more expression kinds.
             elif (
-                isinstance(node, (CallExpr, ListExpr, TupleExpr, DictExpr, OpExpr, MemberExpr))
+                (
+                    isinstance(node, (CallExpr, ListExpr, TupleExpr, DictExpr, OpExpr))
+                    # Only cache non-static access, it may be slow, and may freshen type vars.
+                    or isinstance(node, MemberExpr)
+                    and node.node is None
+                )
                 and not (self.in_lambda_expr or self.chk.current_node_deferred)
                 and not self.chk.options.disable_expression_cache
             ):

mypy/constraints.py

@@ -311,7 +311,13 @@ def infer_constraints(
         for (t, a) in reversed(type_state.inferring)
     ):
         return []
-    if has_recursive_types(template) or isinstance(get_proper_type(template), Instance):
+    # This guard matches the one we use for subtyping, it is slightly more risky,
+    # but it is much faster than has_recursive_types().
+    if (
+        isinstance(template, TypeAliasType)
+        and template.is_recursive
+        or isinstance(get_proper_type(template), Instance)
+    ):
         # This case requires special care because it may cause infinite recursion.
         # Note that we include Instances because the may be recursive as str(Sequence[str]).
         if not has_type_vars(template):
@@ -529,6 +535,8 @@ def handle_recursive_union(template: UnionType, actual: Type, direction: int) ->
     # the union in two parts, and try inferring sequentially.
     non_type_var_items = [t for t in template.items if not isinstance(t, TypeVarType)]
     type_var_items = [t for t in template.items if isinstance(t, TypeVarType)]
+    if not type_var_items or not non_type_var_items:
+        return []
     return infer_constraints(
         UnionType.make_union(non_type_var_items), actual, direction
     ) or infer_constraints(UnionType.make_union(type_var_items), actual, direction)

mypy/infer.py

@@ -8,6 +8,7 @@
 from mypy.constraints import (
     SUBTYPE_OF,
     SUPERTYPE_OF,
+    Constraint,
     infer_constraints,
     infer_constraints_for_callable,
 )
@@ -40,6 +41,7 @@ def infer_function_type_arguments(
     context: ArgumentInferContext,
     strict: bool = True,
     allow_polymorphic: bool = False,
+    extra_constraints: list[Constraint] | None = None,
 ) -> tuple[list[Type | None], list[TypeVarLikeType]]:
     """Infer the type arguments of a generic function.
 
@@ -58,6 +60,8 @@ def infer_function_type_arguments(
     constraints = infer_constraints_for_callable(
         callee_type, arg_types, arg_kinds, arg_names, formal_to_actual, context
     )
+    if extra_constraints:
+        constraints += extra_constraints
 
     # Solve constraints.
     type_vars = callee_type.variables
@@ -71,10 +75,11 @@ def infer_type_arguments(
     is_supertype: bool = False,
     skip_unsatisfied: bool = False,
     erase_types: bool = True,
-) -> list[Type | None]:
+) -> tuple[list[Type | None], list[Constraint]]:
     # Like infer_function_type_arguments, but only match a single type
     # against a generic type.
     constraints = infer_constraints(
         template, actual, SUPERTYPE_OF if is_supertype else SUBTYPE_OF, erase_types=erase_types
     )
-    return solve_constraints(type_vars, constraints, skip_unsatisfied=skip_unsatisfied)[0]
+    solutions, _ = solve_constraints(type_vars, constraints, skip_unsatisfied=skip_unsatisfied)
+    return solutions, constraints

mypy/join.py

@@ -829,8 +829,11 @@ def join_similar_callables(t: CallableType, s: CallableType) -> CallableType:
     # The result should always use 'function' as a fallback if either operands are using it.
     if t.fallback.type.fullname == "builtins.function":
         fallback = t.fallback
-    else:
+    elif s.fallback.type.fullname == "builtins.function":
         fallback = s.fallback
+    else:
+        fallback = InstanceJoiner().join_instances(t.fallback, s.fallback)
+        assert isinstance(fallback, Instance)
     instance_type = None
     if t.instance_type is not None and s.instance_type is not None:
         instance_type = join_types(t.instance_type, s.instance_type)
@@ -888,8 +891,11 @@ def combine_similar_callables(t: CallableType, s: CallableType) -> CallableType:
     # The result should always use 'function' as a fallback if either operands are using it.
     if t.fallback.type.fullname == "builtins.function":
         fallback = t.fallback
-    else:
+    elif s.fallback.type.fullname == "builtins.function":
         fallback = s.fallback
+    else:
+        fallback = InstanceJoiner().join_instances(t.fallback, s.fallback)
+        assert isinstance(fallback, Instance)
     instance_type = None
     if t.instance_type is not None and s.instance_type is not None:
         instance_type = join_types(t.instance_type, s.instance_type)

mypy/messages.py

@@ -3136,7 +3136,7 @@ def [T <: int] f(self, x: int, y: T) -> None
         # TODO: avoid different logic for incremental runs.
         first_arg = get_first_arg(tp)
 
-    if tp.is_type_obj():
+    if tp.is_type_obj() or not tp.is_bound:
         skip_self = True
     if first_arg and not skip_self:
         if s:

mypy/typeops.py

@@ -552,7 +552,7 @@ def bind_self_inner(
         self_vars = [tv for tv in func.variables if tv.id in self_ids]
 
         # Solve for these type arguments using the actual class or instance type.
-        typeargs = infer_type_arguments(
+        typeargs, _ = infer_type_arguments(
             self_vars, self_param_type, original_type, is_supertype=True, erase_types=False
         )
         if (
@@ -561,7 +561,7 @@ def bind_self_inner(
             and isinstance(original_type, (Instance, TypeVarType, TupleType))
         ):
             # In case we call a classmethod through an instance x, fallback to type(x).
-            typeargs = infer_type_arguments(
+            typeargs, _ = infer_type_arguments(
                 self_vars,
                 self_param_type,
                 TypeType(original_type),

test-data/unit/check-functions.test

@@ -3957,3 +3957,25 @@ Ex = TypeVar("Ex", covariant=True)
 
 def takes_lambda(func: Callable[[Ex], Any]) -> None:
     pass
+
+[case testTypeObjectJoinWithOverloadsCorrectFallback]
+from typing import Iterable, overload
+
+class M(type): ...
+class A(metaclass=M): ...
+class B: ...
+class C(metaclass=M):
+    @overload
+    def __init__(self, x: int) -> None: ...
+    @overload
+    def __init__(self, x: str) -> None: ...
+    def __init__(self, x):
+        pass
+
+def f(x: Iterable[object]) -> None: ...
+f([A, B, C])
+f([B, A, C])
+f([B, C, A])
+f([A, C, B])
+f([C, A, B])
+f([C, B, A])

test-data/unit/check-inference-context.test

@@ -1635,3 +1635,48 @@ def foo(args: Union[Iterable[Union[str, int]], str, int]) -> Iterable[str]:
     )
     return args
 [builtins fixtures/isinstancelist.pyi]
+
+[case testInferenceContextBothSidesInvariant]
+from typing import TypeVar, Generic
+
+T = TypeVar("T")
+
+class B(Generic[T]): ...
+class C(B[int]): ...
+
+def first(xs: list[T]) -> T: ...
+
+b: B[int]
+cs: list[C]
+b = first(cs)  # OK
+reveal_type(b)  # N: Revealed type is "__main__.C"
+
+[case testInferenceContextBothSidesNarrow]
+from typing import TypeVar, Generic
+
+T = TypeVar("T")
+
+class B(Generic[T]): ...
+class C(B[int]): ...
+
+def same(x: T) -> T: ...
+
+b: B[int]
+b = same(C())  # This should narrow
+reveal_type(b)  # N: Revealed type is "__main__.C"
+
+[case testInferenceContextBothSidesJoin]
+from typing import TypeVar, Generic, Callable, Union
+
+T = TypeVar("T")
+
+class A: ...
+class B: ...
+class C: ...
+
+def make(x: T) -> Callable[[T], None]: ...
+
+x: Union[B, C]
+fn: Callable[[Union[A, B]], None]
+fn = make(x)
+reveal_type(fn)  # N: Revealed type is "def (__main__.B | __main__.C | __main__.A)"

test-data/unit/check-parameter-specification.test

@@ -2814,6 +2814,20 @@ x: Union[Any, C[[Any, Any]]]
 
 def test(x: int) -> None: ...
 
-x = foo(test)  # E: Argument 1 to "foo" has incompatible type "Callable[[int], None]"; expected "Callable[[Any, Any], None]"
-reveal_type(x)  # N: Revealed type is "__main__.C[[Any, Any]]"
+x = foo(test)
+reveal_type(x)  # N: Revealed type is "__main__.C[Any] | __main__.C[[Any, Any]]"
+[builtins fixtures/paramspec.pyi]
+
+[case testTwoSidedInferenceWithParamSpec]
+from typing import Callable, Generic, TypeVar
+from typing_extensions import ParamSpec
+
+P = ParamSpec("P")
+T = TypeVar("T")
+class C(Generic[P, T]): ...
+
+def thing(func: Callable[P, T], *args: P.args, **kwargs: P.kwargs) -> C[P, T]: ...
+
+def test(x: int = 0) -> None: ...
+f: C[[], None] = thing(test)
 [builtins fixtures/paramspec.pyi]