Various updates to 1.19 changelog

Author: JukkaL

CHANGELOG.md

@@ -12,51 +12,137 @@ improvements and bug fixes. You can install it as follows:
 
 You can read the full documentation for this release on [Read the Docs](http://mypy.readthedocs.io).
 
-### Performance improvements
+### Performance Improvements
 - Switch to a more dynamic SCC processing logic (Ivan Levkivskyi, PR [20053](https://github.com/python/mypy/pull/20053))
-- Try some aliases speed-up (Ivan Levkivskyi, PR [19810](https://github.com/python/mypy/pull/19810))
+- Speed up type aliases (Ivan Levkivskyi, PR [19810](https://github.com/python/mypy/pull/19810))
+
+### Fixed‑Format Cache Improvements
+
+Mypy uses a cache by default to speed up incremental runs by reusing partial results
+from earlier runs. Mypy 1.18 added a new binary, fixed-format cache representation as
+an experimental feature. The feature is no longer experimental, and we are planning
+to enable it by default in a future mypy release (possibly 1.20), since it's faster
+and uses less space than the original, JSON-based cache format.
+
+Mypy now has an extra dependency on the `librt` PyPI package, as it's needed for
+cache serialization and deserialization.
+
+Mypy ships with a tool to convert fixed-format cache files to the old JSON format.
+Example of how to use this:
+```
+$ python -m mypy.exportjson .mypy_cache/.../my_module.data.ff
+```
+
+This way existing use cases that parse JSON cache files can be supported when using
+the new format, though an extra conversion step is needed.
+
+This release includes these improvements:
 
-### Fixed‑Format Cache
 - Force-discard cache if cache format changed (Ivan Levkivskyi, PR [20152](https://github.com/python/mypy/pull/20152))
+- Add tool to convert binary cache files to JSON (Jukka Lehtosalo, PR [20071](https://github.com/python/mypy/pull/20071))
 - Use more efficient serialization format for long integers in cache files (Jukka Lehtosalo, PR [20151](https://github.com/python/mypy/pull/20151))
-- More robust packing of flats in FF cache (Ivan Levkivskyi, PR [20150](https://github.com/python/mypy/pull/20150))
+- More robust packing of flats in fixed-format cache (Ivan Levkivskyi, PR [20150](https://github.com/python/mypy/pull/20150))
 - Use self-descriptive cache with type tags (Ivan Levkivskyi, PR [20137](https://github.com/python/mypy/pull/20137))
 - Use fixed format for cache metas (Ivan Levkivskyi, PR [20088](https://github.com/python/mypy/pull/20088))
 - Make metas more compact; fix indirect suppression (Ivan Levkivskyi, PR [20075](https://github.com/python/mypy/pull/20075))
-- Add tool to convert binary cache files to JSON (Jukka Lehtosalo, PR [20071](https://github.com/python/mypy/pull/20071))
-- Use dedicated tags for most common instances (Ivan Levkivskyi, PR [19762](https://github.com/python/mypy/pull/19762))
+- Use dedicated tags for most common cached instances (Ivan Levkivskyi, PR [19762](https://github.com/python/mypy/pull/19762))
+
+### PEP 747: Annotating Type Forms
+
+Mypy now recognizes `TypeForm[T]` as a type and implements
+[PEP 747](https://peps.python.org/pep-0747/). The feature is still experimental,
+and it's disabled by default. Use `--enable-incomplete-feature=TypeForm` to
+enable type forms. A type form object captures the type information provided by a
+runtime type expression. Example:
+
+```python
+from typing_extensions import TypeForm
 
-### PEP 747 - Annotating Type Forms
-- [PEP 747] Recognize `TypeForm[T]` type and values (#9773) (David Foster, PR [19596](https://github.com/python/mypy/pull/19596))
+def trycast[T](typx: TypeForm[T], value: object) -> T | None: ...
 
-### Fixes to crashes
+def example(o: object) -> None:
+    # 'int | str' below is an expression that represents a type.
+    # Unlike type[T], TypeForm[T] can be used with all kinds of types,
+    # including union types.
+    x = trycast(int | str, o)
+    if x is not None:
+        # Type of 'x' is 'int | str' here
+        ...
+```
+
+This feature was contributed by David Foster (PR [19596](https://github.com/python/mypy/pull/19596)).
+
+### Fixes to Crashes
 - Do not push partial types to the binder (Stanislav Terliakov, PR [20202](https://github.com/python/mypy/pull/20202))
 - Fix crash on recursive tuple with Hashable (Ivan Levkivskyi, PR [20232](https://github.com/python/mypy/pull/20232))
-- Do not assume that args of decorated functions can be cleanly mapped to their nodes (Stanislav Terliakov, PR [20203](https://github.com/python/mypy/pull/20203))
+- Fix crash related to decorated functions (Stanislav Terliakov, PR [20203](https://github.com/python/mypy/pull/20203))
 - Do not abort constructing TypeAlias if only type parameters hold us back (Stanislav Terliakov, PR [20162](https://github.com/python/mypy/pull/20162))
 - Use the fallback for `ModuleSpec` early if it can never be resolved (Stanislav Terliakov, PR [20167](https://github.com/python/mypy/pull/20167))
 - Do not store deferred NamedTuple fields as redefinitions (Stanislav Terliakov, PR [20147](https://github.com/python/mypy/pull/20147))
-- Discard partials remaining after inference failure (Stanislav Terliakov, PR [20126](https://github.com/python/mypy/pull/20126))
-- Remember the pair in `is_overlapping_types` if at least one of them is an alias (Stanislav Terliakov, PR [20127](https://github.com/python/mypy/pull/20127))
+- Discard partial types remaining after inference failure (Stanislav Terliakov, PR [20126](https://github.com/python/mypy/pull/20126))
+- Fix an infinite recursion bug (Stanislav Terliakov, PR [20127](https://github.com/python/mypy/pull/20127))
 - Fix IsADirectoryError for namespace packages when using --linecoverage-report (wyattscarpenter, PR [20109](https://github.com/python/mypy/pull/20109))
-- Fix an INTERNAL ERROR when creating cobertura output for namespace package (wyattscarpenter, PR [20112](https://github.com/python/mypy/pull/20112))
+- Fix an internal error when creating cobertura output for namespace package (wyattscarpenter, PR [20112](https://github.com/python/mypy/pull/20112))
 - Allow type parameters reusing the name missing from current module (Stanislav Terliakov, PR [20081](https://github.com/python/mypy/pull/20081))
-- Prevent TypeGuardedType leak from `narrow_declared_type` as part of typevar bound (Stanislav Terliakov, PR [20046](https://github.com/python/mypy/pull/20046))
+- Prevent TypeGuardedType leak from narrowing declared type as part of type variable bound (Stanislav Terliakov, PR [20046](https://github.com/python/mypy/pull/20046))
 - Fix crash on invalid unpack in base class (Ivan Levkivskyi, PR [19962](https://github.com/python/mypy/pull/19962))
 - Traverse ParamSpec prefix where we should (Ivan Levkivskyi, PR [19800](https://github.com/python/mypy/pull/19800))
+- Fix daemon crash related to imports (Ivan Levkivskyi, PR [20271](https://github.com/python/mypy/pull/20271))
 
 ### Mypyc: Support for `__getattr__`, `__setattr__`, and `__delattr__`
-- Support deleting attributes in `__setattr__` wrapper (Piotr Sawicki, PR [19997](https://github.com/python/mypy/pull/19997))
+
+Mypyc now has partial support for `__getattr__`, `__setattr__` and
+`__delattr__` methods in native classes.
+
+Note that native attributes are not stored using `__dict__`. Setting attributes
+directly while bypassing `__setattr__` is possible by using
+`super().__setattr__(...)` or `object.__setattr__(...)`, but not via `__dict__`.
+
+Example:
+```python
+class Demo:
+    _data: dict[str, str]
+
+    def __init__(self) -> None:
+        # Initialize data dict without calling our __setattr__
+        super().__setattr__("_data", {})
+
+    def __setattr__(self, name: str, value: str) -> None:
+        print(f"Setting {name} = {value!r}")
+
+        if name == "_data":
+            raise AttributeError("'_data' cannot be set")
+
+        self._data[name] = value
+
+    def __getattr__(self, name: str) -> str:
+        print(f"Getting {name}")
+
+        try:
+            return self._data[name]
+        except KeyError:
+            raise AttributeError(name)
+
+d = Demo()
+d.x = "hello"
+d.y = "world"
+
+print(d.x)
+print(d.y)
+```
+
+Related PRs:
 - Generate `__setattr__` wrapper (Piotr Sawicki, PR [19937](https://github.com/python/mypy/pull/19937))
 - Generate `__getattr__` wrapper (Piotr Sawicki, PR [19909](https://github.com/python/mypy/pull/19909))
+- Support deleting attributes in `__setattr__` wrapper (Piotr Sawicki, PR [19997](https://github.com/python/mypy/pull/19997))
 
 ### Miscellaneous Mypyc Improvements
 - Fix crash on `super` in generator (Ivan Levkivskyi, PR [20291](https://github.com/python/mypy/pull/20291))
 - Fix calling base class async method using `super()` (Jukka Lehtosalo, PR [20254](https://github.com/python/mypy/pull/20254))
 - Fix async or generator methods in traits (Jukka Lehtosalo, PR [20246](https://github.com/python/mypy/pull/20246))
-- Optimize equality check with string literals [1/1] (BobTheBuidler, PR [19883](https://github.com/python/mypy/pull/19883))
+- Optimize equality check with string literals (BobTheBuidler, PR [19883](https://github.com/python/mypy/pull/19883))
 - Fix inheritance of async defs (Jukka Lehtosalo, PR [20044](https://github.com/python/mypy/pull/20044))
-- Reject invalid `mypyc_attr` args [1/1] (BobTheBuidler, PR [19963](https://github.com/python/mypy/pull/19963))
+- Reject invalid `mypyc_attr` args (BobTheBuidler, PR [19963](https://github.com/python/mypy/pull/19963))
 - Optimize `isinstance` with tuple of primitive types (BobTheBuidler, PR [19949](https://github.com/python/mypy/pull/19949))
 - Optimize away first index check in for loops if length > 1 (BobTheBuidler, PR [19933](https://github.com/python/mypy/pull/19933))
 - Fix broken exception/cancellation handling in async def (Jukka Lehtosalo, PR [19951](https://github.com/python/mypy/pull/19951))
@@ -71,45 +157,42 @@ You can read the full documentation for this release on [Read the Docs](http://m
 ### Stubtest Improvements
 - Check `_value_` for ellipsis-valued stub enum members (Stanislav Terliakov, PR [19760](https://github.com/python/mypy/pull/19760))
 - Include function name in overload assertion messages (Joren Hammudoglu, PR [20063](https://github.com/python/mypy/pull/20063))
-- Small fix in get_default_function_sig (iap, PR [19822](https://github.com/python/mypy/pull/19822))
-- Adjust stubtest test stubs for PEP 728 (Python 3.15) (Marc Mueller, PR [20009](https://github.com/python/mypy/pull/20009))
+- Fix special case in analyzing function signature (iap, PR [19822](https://github.com/python/mypy/pull/19822))
 - Improve `allowlist` docs with better example (sobolevn, PR [20007](https://github.com/python/mypy/pull/20007))
 
 ### Documentation Updates
-- Update duck_type_compatibility.rst: mention strict-bytes & mypy 2.0 (wyattscarpenter, PR [20121](https://github.com/python/mypy/pull/20121))
-- document --enable-incomplete-feature TypeForm, minimally but sufficiently (wyattscarpenter, PR [20173](https://github.com/python/mypy/pull/20173))
-- Change the InlineTypedDict example (wyattscarpenter, PR [20172](https://github.com/python/mypy/pull/20172))
-- Update kinds_of_types.rst: keep old anchor for #no-strict-optional (wyattscarpenter, PR [19828](https://github.com/python/mypy/pull/19828))
+- Update duck type compatibility: mention strict-bytes and mypy 2.0 (wyattscarpenter, PR [20121](https://github.com/python/mypy/pull/20121))
+- Document `--enable-incomplete-feature TypeForm` (wyattscarpenter, PR [20173](https://github.com/python/mypy/pull/20173))
+- Change the inline TypedDict example (wyattscarpenter, PR [20172](https://github.com/python/mypy/pull/20172))
 - Replace `List` with built‑in `list` (PEP 585) (Thiago J. Barbalho, PR [20000](https://github.com/python/mypy/pull/20000))
-- main.py: junit documentation elaboration (wyattscarpenter, PR [19867](https://github.com/python/mypy/pull/19867))
+- Improve junit documentation (wyattscarpenter, PR [19867](https://github.com/python/mypy/pull/19867))
 
 ### Other Notable Fixes and Improvements
-- Update import map when new modules added (Ivan Levkivskyi, PR [20271](https://github.com/python/mypy/pull/20271))
 - Fix annotated with function as type keyword list parameter (KarelKenens, PR [20094](https://github.com/python/mypy/pull/20094))
 - Fix errors for raise NotImplemented (Shantanu, PR [20168](https://github.com/python/mypy/pull/20168))
 - Don't let help formatter line-wrap URLs (Frank Dana, PR [19825](https://github.com/python/mypy/pull/19825))
 - Do not cache fast container types inside lambdas (Stanislav Terliakov, PR [20166](https://github.com/python/mypy/pull/20166))
 - Respect force-union-syntax flag in error hint (Marc Mueller, PR [20165](https://github.com/python/mypy/pull/20165))
 - Fix type checking of dict type aliases (Shantanu, PR [20170](https://github.com/python/mypy/pull/20170))
-- Use pretty_callable more often for callable expressions (Theodore Ando, PR [20128](https://github.com/python/mypy/pull/20128))
+- Use pretty callable formatting more often for callable expressions (Theodore Ando, PR [20128](https://github.com/python/mypy/pull/20128))
 - Use dummy concrete type instead of `Any` when checking protocol variance (bzoracler, PR [20110](https://github.com/python/mypy/pull/20110))
-- [PEP 696] Fix swapping TypeVars with defaults (Randolf Scholz, PR [19449](https://github.com/python/mypy/pull/19449))
-- Fix narrowing of class pattern with union-argument (Randolf Scholz, PR [19517](https://github.com/python/mypy/pull/19517))
+- PEP 696: Fix swapping TypeVars with defaults (Randolf Scholz, PR [19449](https://github.com/python/mypy/pull/19449))
+- Fix narrowing of class pattern with union type (Randolf Scholz, PR [19517](https://github.com/python/mypy/pull/19517))
 - Do not emit unreachable warnings for lines that return `NotImplemented` (Christoph Tyralla, PR [20083](https://github.com/python/mypy/pull/20083))
-- fix matching against `typing.Callable` and `Protocol` types (Randolf Scholz, PR [19471](https://github.com/python/mypy/pull/19471))
-- Make --pretty work better on multi-line issues (A5rocks, PR [20056](https://github.com/python/mypy/pull/20056))
+- Fix matching against `typing.Callable` and `Protocol` types (Randolf Scholz, PR [19471](https://github.com/python/mypy/pull/19471))
+- Make `--pretty` work better on multi-line issues (A5rocks, PR [20056](https://github.com/python/mypy/pull/20056))
 - More precise return types for `TypedDict.get` (Randolf Scholz, PR [19897](https://github.com/python/mypy/pull/19897))
-- prevent false unreachable warnings for @final instances that occur when strict optional checking is disabled (Christoph Tyralla, PR [20045](https://github.com/python/mypy/pull/20045))
+- Prevent false unreachable warnings for `@final` instances that occur when strict optional checking is disabled (Christoph Tyralla, PR [20045](https://github.com/python/mypy/pull/20045))
 - Check class references to catch non-existent classes in match cases (A5rocks, PR [20042](https://github.com/python/mypy/pull/20042))
 - Do not sort unused error codes in unused error codes warning (wyattscarpenter, PR [20036](https://github.com/python/mypy/pull/20036))
-- Fix `[name-defined]` false-positive in `class A[X, Y=X]:` case (sobolevn, PR [20021](https://github.com/python/mypy/pull/20021))
+- Fix `[name-defined]` false positive in `class A[X, Y=X]:` case (sobolevn, PR [20021](https://github.com/python/mypy/pull/20021))
 - Filter SyntaxWarnings during AST parsing (Marc Mueller, PR [20023](https://github.com/python/mypy/pull/20023))
-- Make untyped decorator its own code (wyattscarpenter, PR [19911](https://github.com/python/mypy/pull/19911))
+- Make untyped decorator its own error code (wyattscarpenter, PR [19911](https://github.com/python/mypy/pull/19911))
 - Support error codes from plugins in options (Sigve Sebastian Farstad, PR [19719](https://github.com/python/mypy/pull/19719))
 - Allow returning Literals in `__new__` (James Hilton-Balfe, PR [15687](https://github.com/python/mypy/pull/15687))
 - Inverse interface freshness logic (Ivan Levkivskyi, PR [19809](https://github.com/python/mypy/pull/19809))
 - Do not report exhaustive-match after deferral (Stanislav Terliakov, PR [19804](https://github.com/python/mypy/pull/19804))
-- Make untyped_calls_exclude invalidate cache (Ivan Levkivskyi, PR [19801](https://github.com/python/mypy/pull/19801))
+- Make `untyped_calls_exclude` invalidate cache (Ivan Levkivskyi, PR [19801](https://github.com/python/mypy/pull/19801))
 - Add await to empty context hack (Stanislav Terliakov, PR [19777](https://github.com/python/mypy/pull/19777))
 - Consider non-empty enums assignable to Self (Stanislav Terliakov, PR [19779](https://github.com/python/mypy/pull/19779))