Optimize CallableType.formal_arguments (#11543)

Don't use a generator, since they tend to be slow when compiled.

This method came up as a hot spot when profiling compiled mypy.

Author: JukkaL

mypy/types.py

@@ -7,7 +7,7 @@
 
 from typing import (
     Any, TypeVar, Dict, List, Tuple, cast, Set, Optional, Union, Iterable, NamedTuple,
-    Sequence, Iterator
+    Sequence
 )
 from typing_extensions import ClassVar, Final, TYPE_CHECKING, overload, TypeAlias as _TypeAlias
 
@@ -1168,14 +1168,15 @@ def max_possible_positional_args(self) -> int:
             return sys.maxsize
         return sum([kind.is_positional() for kind in self.arg_kinds])
 
-    def formal_arguments(self, include_star_args: bool = False) -> Iterator[FormalArgument]:
+    def formal_arguments(self, include_star_args: bool = False) -> List[FormalArgument]:
         """Yields the formal arguments corresponding to this callable, ignoring *arg and **kwargs.
 
         To handle *args and **kwargs, use the 'callable.var_args' and 'callable.kw_args' fields,
         if they are not None.
 
         If you really want to include star args in the yielded output, set the
         'include_star_args' parameter to 'True'."""
+        args = []
         done_with_positional = False
         for i in range(len(self.arg_types)):
             kind = self.arg_kinds[i]
@@ -1186,11 +1187,14 @@ def formal_arguments(self, include_star_args: bool = False) -> Iterator[FormalAr
 
             required = kind.is_required()
             pos = None if done_with_positional else i
-            yield FormalArgument(
+            arg = FormalArgument(
                 self.arg_names[i],
                 pos,
                 self.arg_types[i],
-                required)
+                required
+            )
+            args.append(arg)
+        return args
 
     def argument_by_name(self, name: Optional[str]) -> Optional[FormalArgument]:
         if name is None: