Two more micro-optimizations (#19627)

This has two things (totalling 1.5% locally, but see caveat below):
* Do not use `@contextmanger` (that is relatively slow) for
`local_type_map`, since it appears in multiple hot paths.
* Do not show name suggestions for import errors in third party packages
(since those errors are ignored anyway). It calls `difflib` that can be
extremely slow with large modules.

Btw the second will probably not affect self-check, although it did
affect _my_ self-check, since apparently `pytest` depends on `numpy`.
Well, they don't specify it as a package dependency, but
https://github.com/pytest-dev/pytest/blob/main/src/_pytest/python_api.py#L17-L18
```python
if TYPE_CHECKING:
    from numpy import ndarray
```
(and I have numpy installed in all my environments, LOL)

Author: ilevkivskyi

mypy/checker.py

@@ -6,7 +6,18 @@
 from collections import defaultdict
 from collections.abc import Iterable, Iterator, Mapping, Sequence, Set as AbstractSet
 from contextlib import ExitStack, contextmanager
-from typing import Callable, Final, Generic, NamedTuple, Optional, TypeVar, Union, cast, overload
+from typing import (
+    Callable,
+    Final,
+    Generic,
+    Literal,
+    NamedTuple,
+    Optional,
+    TypeVar,
+    Union,
+    cast,
+    overload,
+)
 from typing_extensions import TypeAlias as _TypeAlias, TypeGuard
 
 import mypy.checkexpr
@@ -277,6 +288,26 @@ class PartialTypeScope(NamedTuple):
     is_local: bool
 
 
+class LocalTypeMap:
+    """Store inferred types into a temporary type map (returned).
+
+    This can be used to perform type checking "experiments" without
+    affecting exported types (which are used by mypyc).
+    """
+
+    def __init__(self, chk: TypeChecker) -> None:
+        self.chk = chk
+
+    def __enter__(self) -> dict[Expression, Type]:
+        temp_type_map: dict[Expression, Type] = {}
+        self.chk._type_maps.append(temp_type_map)
+        return temp_type_map
+
+    def __exit__(self, exc_type: object, exc_val: object, exc_tb: object) -> Literal[False]:
+        self.chk._type_maps.pop()
+        return False
+
+
 class TypeChecker(NodeVisitor[None], TypeCheckerSharedApi):
     """Mypy type checker.
 
@@ -402,6 +433,7 @@ def __init__(
         self.is_typeshed_stub = tree.is_typeshed_file(options)
         self.inferred_attribute_types = None
         self.allow_constructor_cache = True
+        self.local_type_map = LocalTypeMap(self)
 
         # If True, process function definitions. If False, don't. This is used
         # for processing module top levels in fine-grained incremental mode.
@@ -4631,7 +4663,7 @@ def check_simple_assignment(
                 # may cause some perf impact, plus we want to partially preserve
                 # the old behavior. This helps with various practical examples, see
                 # e.g. testOptionalTypeNarrowedByGenericCall.
-                with self.msg.filter_errors() as local_errors, self.local_type_map() as type_map:
+                with self.msg.filter_errors() as local_errors, self.local_type_map as type_map:
                     alt_rvalue_type = self.expr_checker.accept(
                         rvalue, None, always_allow_any=always_allow_any
                     )
@@ -7458,18 +7490,6 @@ def lookup_type(self, node: Expression) -> Type:
     def store_types(self, d: dict[Expression, Type]) -> None:
         self._type_maps[-1].update(d)
 
-    @contextmanager
-    def local_type_map(self) -> Iterator[dict[Expression, Type]]:
-        """Store inferred types into a temporary type map (returned).
-
-        This can be used to perform type checking "experiments" without
-        affecting exported types (which are used by mypyc).
-        """
-        temp_type_map: dict[Expression, Type] = {}
-        self._type_maps.append(temp_type_map)
-        yield temp_type_map
-        self._type_maps.pop()
-
     def in_checked_function(self) -> bool:
         """Should we type-check the current function?
 

mypy/checkexpr.py

@@ -1075,7 +1075,7 @@ def check_typeddict_call_with_kwargs(
 
         # We don't show any errors, just infer types in a generic TypedDict type,
         # a custom error message will be given below, if there are errors.
-        with self.msg.filter_errors(), self.chk.local_type_map():
+        with self.msg.filter_errors(), self.chk.local_type_map:
             orig_ret_type, _ = self.check_callable_call(
                 infer_callee,
                 # We use first expression for each key to infer type variables of a generic
@@ -1440,7 +1440,7 @@ def is_generic_decorator_overload_call(
             return None
         if not isinstance(get_proper_type(callee_type.ret_type), CallableType):
             return None
-        with self.chk.local_type_map():
+        with self.chk.local_type_map:
             with self.msg.filter_errors():
                 arg_type = get_proper_type(self.accept(args[0], type_context=None))
         if isinstance(arg_type, Overloaded):
@@ -2920,7 +2920,7 @@ def infer_overload_return_type(
         for typ in plausible_targets:
             assert self.msg is self.chk.msg
             with self.msg.filter_errors() as w:
-                with self.chk.local_type_map() as m:
+                with self.chk.local_type_map as m:
                     ret_type, infer_type = self.check_call(
                         callee=typ,
                         args=args,
@@ -5367,7 +5367,7 @@ def visit_dict_expr(self, e: DictExpr) -> Type:
                 return self.check_typeddict_literal_in_context(e, typeddict_contexts[0])
             # Multiple items union, check if at least one of them matches cleanly.
             for typeddict_context in typeddict_contexts:
-                with self.msg.filter_errors() as err, self.chk.local_type_map() as tmap:
+                with self.msg.filter_errors() as err, self.chk.local_type_map as tmap:
                     ret_type = self.check_typeddict_literal_in_context(e, typeddict_context)
                 if err.has_new_errors():
                     continue
@@ -6095,15 +6095,12 @@ def accept(
 
     def accept_maybe_cache(self, node: Expression, type_context: Type | None = None) -> Type:
         binder_version = self.chk.binder.version
-        # Micro-optimization: inline local_type_map() as it is somewhat slow in mypyc.
-        type_map: dict[Expression, Type] = {}
-        self.chk._type_maps.append(type_map)
         with self.msg.filter_errors(filter_errors=True, save_filtered_errors=True) as msg:
-            typ = node.accept(self)
+            with self.chk.local_type_map as type_map:
+                typ = node.accept(self)
         messages = msg.filtered_errors()
         if binder_version == self.chk.binder.version and not self.chk.current_node_deferred:
             self.expr_cache[(node, type_context)] = (binder_version, typ, messages, type_map)
-        self.chk._type_maps.pop()
         self.chk.store_types(type_map)
         self.msg.add_errors(messages)
         return typ

mypy/semanal.py

@@ -3048,7 +3048,9 @@ def report_missing_module_attribute(
                 message = (
                     f'Module "{import_id}" does not explicitly export attribute "{source_id}"'
                 )
-            else:
+            elif not (
+                self.options.ignore_errors or self.cur_mod_node.path in self.errors.ignored_files
+            ):
                 alternatives = set(module.names.keys()).difference({source_id})
                 matches = best_matches(source_id, alternatives, n=3)
                 if matches: