Move apply_type() to applytype.py (#17346)

Moving towards #15907

This is a pure refactoring. It was surprisingly easy, this didn't add
new import cycles, because there is already (somewhat fundamental) cycle
`applytype.py` <-> `subtypes.py`.

mypy/applytype.py

@@ -1,24 +1,32 @@
 from __future__ import annotations
 
-from typing import Callable, Sequence
+from typing import Callable, Iterable, Sequence
 
 import mypy.subtypes
 from mypy.erasetype import erase_typevars
 from mypy.expandtype import expand_type
-from mypy.nodes import Context
+from mypy.nodes import Context, TypeInfo
+from mypy.type_visitor import TypeTranslator
+from mypy.typeops import get_all_type_vars
 from mypy.types import (
     AnyType,
     CallableType,
+    Instance,
+    Parameters,
+    ParamSpecFlavor,
     ParamSpecType,
     PartialType,
+    ProperType,
     Type,
+    TypeAliasType,
     TypeVarId,
     TypeVarLikeType,
     TypeVarTupleType,
     TypeVarType,
     UninhabitedType,
     UnpackType,
     get_proper_type,
+    remove_dups,
 )
 
 
@@ -170,3 +178,126 @@ def apply_generic_arguments(
         type_guard=type_guard,
         type_is=type_is,
     )
+
+
+def apply_poly(tp: CallableType, poly_tvars: Sequence[TypeVarLikeType]) -> CallableType | None:
+    """Make free type variables generic in the type if possible.
+
+    This will translate the type `tp` while trying to create valid bindings for
+    type variables `poly_tvars` while traversing the type. This follows the same rules
+    as we do during semantic analysis phase, examples:
+      * Callable[Callable[[T], T], T] -> def [T] (def (T) -> T) -> T
+      * Callable[[], Callable[[T], T]] -> def () -> def [T] (T -> T)
+      * List[T] -> None (not possible)
+    """
+    try:
+        return tp.copy_modified(
+            arg_types=[t.accept(PolyTranslator(poly_tvars)) for t in tp.arg_types],
+            ret_type=tp.ret_type.accept(PolyTranslator(poly_tvars)),
+            variables=[],
+        )
+    except PolyTranslationError:
+        return None
+
+
+class PolyTranslationError(Exception):
+    pass
+
+
+class PolyTranslator(TypeTranslator):
+    """Make free type variables generic in the type if possible.
+
+    See docstring for apply_poly() for details.
+    """
+
+    def __init__(
+        self,
+        poly_tvars: Iterable[TypeVarLikeType],
+        bound_tvars: frozenset[TypeVarLikeType] = frozenset(),
+        seen_aliases: frozenset[TypeInfo] = frozenset(),
+    ) -> None:
+        self.poly_tvars = set(poly_tvars)
+        # This is a simplified version of TypeVarScope used during semantic analysis.
+        self.bound_tvars = bound_tvars
+        self.seen_aliases = seen_aliases
+
+    def collect_vars(self, t: CallableType | Parameters) -> list[TypeVarLikeType]:
+        found_vars = []
+        for arg in t.arg_types:
+            for tv in get_all_type_vars(arg):
+                if isinstance(tv, ParamSpecType):
+                    normalized: TypeVarLikeType = tv.copy_modified(
+                        flavor=ParamSpecFlavor.BARE, prefix=Parameters([], [], [])
+                    )
+                else:
+                    normalized = tv
+                if normalized in self.poly_tvars and normalized not in self.bound_tvars:
+                    found_vars.append(normalized)
+        return remove_dups(found_vars)
+
+    def visit_callable_type(self, t: CallableType) -> Type:
+        found_vars = self.collect_vars(t)
+        self.bound_tvars |= set(found_vars)
+        result = super().visit_callable_type(t)
+        self.bound_tvars -= set(found_vars)
+
+        assert isinstance(result, ProperType) and isinstance(result, CallableType)
+        result.variables = list(result.variables) + found_vars
+        return result
+
+    def visit_type_var(self, t: TypeVarType) -> Type:
+        if t in self.poly_tvars and t not in self.bound_tvars:
+            raise PolyTranslationError()
+        return super().visit_type_var(t)
+
+    def visit_param_spec(self, t: ParamSpecType) -> Type:
+        if t in self.poly_tvars and t not in self.bound_tvars:
+            raise PolyTranslationError()
+        return super().visit_param_spec(t)
+
+    def visit_type_var_tuple(self, t: TypeVarTupleType) -> Type:
+        if t in self.poly_tvars and t not in self.bound_tvars:
+            raise PolyTranslationError()
+        return super().visit_type_var_tuple(t)
+
+    def visit_type_alias_type(self, t: TypeAliasType) -> Type:
+        if not t.args:
+            return t.copy_modified()
+        if not t.is_recursive:
+            return get_proper_type(t).accept(self)
+        # We can't handle polymorphic application for recursive generic aliases
+        # without risking an infinite recursion, just give up for now.
+        raise PolyTranslationError()
+
+    def visit_instance(self, t: Instance) -> Type:
+        if t.type.has_param_spec_type:
+            # We need this special-casing to preserve the possibility to store a
+            # generic function in an instance type. Things like
+            #     forall T . Foo[[x: T], T]
+            # are not really expressible in current type system, but this looks like
+            # a useful feature, so let's keep it.
+            param_spec_index = next(
+                i for (i, tv) in enumerate(t.type.defn.type_vars) if isinstance(tv, ParamSpecType)
+            )
+            p = get_proper_type(t.args[param_spec_index])
+            if isinstance(p, Parameters):
+                found_vars = self.collect_vars(p)
+                self.bound_tvars |= set(found_vars)
+                new_args = [a.accept(self) for a in t.args]
+                self.bound_tvars -= set(found_vars)
+
+                repl = new_args[param_spec_index]
+                assert isinstance(repl, ProperType) and isinstance(repl, Parameters)
+                repl.variables = list(repl.variables) + list(found_vars)
+                return t.copy_modified(args=new_args)
+        # There is the same problem with callback protocols as with aliases
+        # (callback protocols are essentially more flexible aliases to callables).
+        if t.args and t.type.is_protocol and t.type.protocol_members == ["__call__"]:
+            if t.type in self.seen_aliases:
+                raise PolyTranslationError()
+            call = mypy.subtypes.find_member("__call__", t, t, is_operator=True)
+            assert call is not None
+            return call.accept(
+                PolyTranslator(self.poly_tvars, self.bound_tvars, self.seen_aliases | {t.type})
+            )
+        return super().visit_instance(t)

mypy/checkexpr.py

@@ -115,7 +115,6 @@
     non_method_protocol_members,
 )
 from mypy.traverser import has_await_expression
-from mypy.type_visitor import TypeTranslator
 from mypy.typeanal import (
     check_for_explicit_any,
     fix_instance,
@@ -168,7 +167,6 @@
     TypeOfAny,
     TypeType,
     TypeVarId,
-    TypeVarLikeType,
     TypeVarTupleType,
     TypeVarType,
     UnboundType,
@@ -182,7 +180,6 @@
     get_proper_types,
     has_recursive_types,
     is_named_instance,
-    remove_dups,
     split_with_prefix_and_suffix,
 )
 from mypy.types_utils import (
@@ -2136,7 +2133,7 @@ def infer_function_type_arguments(
                 )
                 # Try applying inferred polymorphic type if possible, e.g. Callable[[T], T] can
                 # be interpreted as def [T] (T) -> T, but dict[T, T] cannot be expressed.
-                applied = apply_poly(poly_callee_type, free_vars)
+                applied = applytype.apply_poly(poly_callee_type, free_vars)
                 if applied is not None and all(
                     a is not None and not isinstance(get_proper_type(a), UninhabitedType)
                     for a in poly_inferred_args
@@ -6220,129 +6217,6 @@ def replace_callable_return_type(c: CallableType, new_ret_type: Type) -> Callabl
     return c.copy_modified(ret_type=new_ret_type)
 
 
-def apply_poly(tp: CallableType, poly_tvars: Sequence[TypeVarLikeType]) -> CallableType | None:
-    """Make free type variables generic in the type if possible.
-
-    This will translate the type `tp` while trying to create valid bindings for
-    type variables `poly_tvars` while traversing the type. This follows the same rules
-    as we do during semantic analysis phase, examples:
-      * Callable[Callable[[T], T], T] -> def [T] (def (T) -> T) -> T
-      * Callable[[], Callable[[T], T]] -> def () -> def [T] (T -> T)
-      * List[T] -> None (not possible)
-    """
-    try:
-        return tp.copy_modified(
-            arg_types=[t.accept(PolyTranslator(poly_tvars)) for t in tp.arg_types],
-            ret_type=tp.ret_type.accept(PolyTranslator(poly_tvars)),
-            variables=[],
-        )
-    except PolyTranslationError:
-        return None
-
-
-class PolyTranslationError(Exception):
-    pass
-
-
-class PolyTranslator(TypeTranslator):
-    """Make free type variables generic in the type if possible.
-
-    See docstring for apply_poly() for details.
-    """
-
-    def __init__(
-        self,
-        poly_tvars: Iterable[TypeVarLikeType],
-        bound_tvars: frozenset[TypeVarLikeType] = frozenset(),
-        seen_aliases: frozenset[TypeInfo] = frozenset(),
-    ) -> None:
-        self.poly_tvars = set(poly_tvars)
-        # This is a simplified version of TypeVarScope used during semantic analysis.
-        self.bound_tvars = bound_tvars
-        self.seen_aliases = seen_aliases
-
-    def collect_vars(self, t: CallableType | Parameters) -> list[TypeVarLikeType]:
-        found_vars = []
-        for arg in t.arg_types:
-            for tv in get_all_type_vars(arg):
-                if isinstance(tv, ParamSpecType):
-                    normalized: TypeVarLikeType = tv.copy_modified(
-                        flavor=ParamSpecFlavor.BARE, prefix=Parameters([], [], [])
-                    )
-                else:
-                    normalized = tv
-                if normalized in self.poly_tvars and normalized not in self.bound_tvars:
-                    found_vars.append(normalized)
-        return remove_dups(found_vars)
-
-    def visit_callable_type(self, t: CallableType) -> Type:
-        found_vars = self.collect_vars(t)
-        self.bound_tvars |= set(found_vars)
-        result = super().visit_callable_type(t)
-        self.bound_tvars -= set(found_vars)
-
-        assert isinstance(result, ProperType) and isinstance(result, CallableType)
-        result.variables = list(result.variables) + found_vars
-        return result
-
-    def visit_type_var(self, t: TypeVarType) -> Type:
-        if t in self.poly_tvars and t not in self.bound_tvars:
-            raise PolyTranslationError()
-        return super().visit_type_var(t)
-
-    def visit_param_spec(self, t: ParamSpecType) -> Type:
-        if t in self.poly_tvars and t not in self.bound_tvars:
-            raise PolyTranslationError()
-        return super().visit_param_spec(t)
-
-    def visit_type_var_tuple(self, t: TypeVarTupleType) -> Type:
-        if t in self.poly_tvars and t not in self.bound_tvars:
-            raise PolyTranslationError()
-        return super().visit_type_var_tuple(t)
-
-    def visit_type_alias_type(self, t: TypeAliasType) -> Type:
-        if not t.args:
-            return t.copy_modified()
-        if not t.is_recursive:
-            return get_proper_type(t).accept(self)
-        # We can't handle polymorphic application for recursive generic aliases
-        # without risking an infinite recursion, just give up for now.
-        raise PolyTranslationError()
-
-    def visit_instance(self, t: Instance) -> Type:
-        if t.type.has_param_spec_type:
-            # We need this special-casing to preserve the possibility to store a
-            # generic function in an instance type. Things like
-            #     forall T . Foo[[x: T], T]
-            # are not really expressible in current type system, but this looks like
-            # a useful feature, so let's keep it.
-            param_spec_index = next(
-                i for (i, tv) in enumerate(t.type.defn.type_vars) if isinstance(tv, ParamSpecType)
-            )
-            p = get_proper_type(t.args[param_spec_index])
-            if isinstance(p, Parameters):
-                found_vars = self.collect_vars(p)
-                self.bound_tvars |= set(found_vars)
-                new_args = [a.accept(self) for a in t.args]
-                self.bound_tvars -= set(found_vars)
-
-                repl = new_args[param_spec_index]
-                assert isinstance(repl, ProperType) and isinstance(repl, Parameters)
-                repl.variables = list(repl.variables) + list(found_vars)
-                return t.copy_modified(args=new_args)
-        # There is the same problem with callback protocols as with aliases
-        # (callback protocols are essentially more flexible aliases to callables).
-        if t.args and t.type.is_protocol and t.type.protocol_members == ["__call__"]:
-            if t.type in self.seen_aliases:
-                raise PolyTranslationError()
-            call = find_member("__call__", t, t, is_operator=True)
-            assert call is not None
-            return call.accept(
-                PolyTranslator(self.poly_tvars, self.bound_tvars, self.seen_aliases | {t.type})
-            )
-        return super().visit_instance(t)
-
-
 class ArgInferSecondPassQuery(types.BoolTypeQuery):
     """Query whether an argument type should be inferred in the second pass.