Rename type alias helper with a misleading name (#15199)

Author: ilevkivskyi

mypy/checkexpr.py

@@ -102,8 +102,8 @@
 from mypy.traverser import has_await_expression
 from mypy.typeanal import (
     check_for_explicit_any,
-    expand_type_alias,
     has_any_from_unimported_type,
+    instantiate_type_alias,
     make_optional_type,
     set_any_tvars,
 )
@@ -3965,12 +3965,12 @@ def visit_type_application(self, tapp: TypeApplication) -> Type:
 
         There are two different options here, depending on whether expr refers
         to a type alias or directly to a generic class. In the first case we need
-        to use a dedicated function typeanal.expand_type_alias(). This
-        is due to some differences in how type arguments are applied and checked.
+        to use a dedicated function typeanal.instantiate_type_alias(). This
+        is due to slight differences in how type arguments are applied and checked.
         """
         if isinstance(tapp.expr, RefExpr) and isinstance(tapp.expr.node, TypeAlias):
             # Subscription of a (generic) alias in runtime context, expand the alias.
-            item = expand_type_alias(
+            item = instantiate_type_alias(
                 tapp.expr.node,
                 tapp.types,
                 self.chk.fail,

mypy/typeanal.py

@@ -398,7 +398,7 @@ def visit_unbound_type_nonoptional(self, t: UnboundType, defining_literal: bool)
                     an_args = self.pack_paramspec_args(an_args)
 
                 disallow_any = self.options.disallow_any_generics and not self.is_typeshed_stub
-                res = expand_type_alias(
+                res = instantiate_type_alias(
                     node,
                     an_args,
                     self.fail,
@@ -408,7 +408,7 @@ def visit_unbound_type_nonoptional(self, t: UnboundType, defining_literal: bool)
                     unexpanded_type=t,
                     disallow_any=disallow_any,
                 )
-                # The only case where expand_type_alias() can return an incorrect instance is
+                # The only case where instantiate_type_alias() can return an incorrect instance is
                 # when it is top-level instance, so no need to recurse.
                 if (
                     isinstance(res, Instance)  # type: ignore[misc]
@@ -714,7 +714,7 @@ def analyze_type_with_type_info(
             # The class has a Tuple[...] base class so it will be
             # represented as a tuple type.
             if info.special_alias:
-                return expand_type_alias(
+                return instantiate_type_alias(
                     info.special_alias,
                     # TODO: should we allow NamedTuples generic in ParamSpec?
                     self.anal_array(args),
@@ -730,7 +730,7 @@ def analyze_type_with_type_info(
             # The class has a TypedDict[...] base class so it will be
             # represented as a typeddict type.
             if info.special_alias:
-                return expand_type_alias(
+                return instantiate_type_alias(
                     info.special_alias,
                     # TODO: should we allow TypedDicts generic in ParamSpec?
                     self.anal_array(args),
@@ -1713,7 +1713,7 @@ def fix_instance(
     t.invalid = True
 
 
-def expand_type_alias(
+def instantiate_type_alias(
     node: TypeAlias,
     args: list[Type],
     fail: MsgCallback,
@@ -1725,11 +1725,13 @@ def expand_type_alias(
     disallow_any: bool = False,
     use_standard_error: bool = False,
 ) -> Type:
-    """Expand a (generic) type alias target following the rules outlined in TypeAlias docstring.
+    """Create an instance of a (generic) type alias from alias node and type arguments.
 
+    We are following the rules outlined in TypeAlias docstring.
     Here:
-        target: original target type
-        args: types to be substituted in place of type variables
+        node: type alias node (definition)
+        args: type arguments (types to be substituted in place of type variables
+              when expanding the alias)
         fail: error reporter callback
         no_args: whether original definition used a bare generic `A = List`
         ctx: context where expansion happens