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[Chore] Update changelog for 2.2 #21691

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277 changes: 277 additions & 0 deletions CHANGELOG.md
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## Next Release

## Mypy 2.2

We've just uploaded mypy 2.2.0 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)).
Mypy is a static type checker for Python. This release includes new features, performance
improvements and bug fixes. You can install it as follows:

python3 -m pip install -U mypy

You can read the full documentation for this release on [Read the Docs](http://mypy.readthedocs.io).

### Support for Closed TypedDicts (PEP 728)

Mypy now supports closed TypedDicts as specified in PEP 728. A closed TypedDict cannot have extra
keys beyond those explicitly defined. This allows the type checker to determine that certain
operations are safe when they otherwise wouldn't be due to the potential presence of unknown keys.

You can use the `closed` keyword argument with `TypedDict`:

```python
HasName = TypedDict("HasName", {"name": str})
HasOnlyName = TypedDict("HasOnlyName", {"name": str}, closed=True)
Movie = TypedDict("Movie", {"name": str, "year": int})

movie: Movie = {"name": "Nimona", "year": 2023}
has_name: HasName = movie # OK: HasName is open (default)
has_only_name: HasOnlyName = movie # Error: HasOnlyName is closed and Movie has extra "year" key
```

Closed TypedDicts enable more precise type checking because the type checker knows exactly which
keys are present. This is particularly useful when working with TypedDict unions or when you want
to ensure that a TypedDict conforms to an exact shape.

The `closed` keyword also enables safe type narrowing with `in` checks:

```python
Book = TypedDict('Book', {'book': str}, closed=True)
DVD = TypedDict('DVD', {'dvd': str}, closed=True)
type Inventory = Book | DVD
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def print_type(inventory: Inventory) -> None:
if "book" in inventory:
# Type is narrowed to Book here - safe because DVD is closed
print(inventory["book"])
else:
# Type is narrowed to DVD here
print(inventory["dvd"])
```

The `closed` keyword is also supported in class-based syntax:

```python
class HasOnlyName(TypedDict, closed=True):
name: str
```

Note that closed TypedDicts are structural types, so a closed TypedDict is assignable to an open
TypedDict with the same keys, but not vice versa.

Contributed by Alice (PR [21382](https://github.com/python/mypy/pull/21382)).

### Complete Support for Type Variable Defaults (PEP 696)

Mypy now has complete support for type variable defaults as specified in PEP 696. This allows you to
specify default values for type parameters in generic classes, functions, and type aliases.

Traditional syntax (Python 3.11 and earlier):

```python
T = TypeVar("T", default=int) # This means that if no type is specified T = int
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@dataclass
class Box(Generic[T]):
value: T | None = None

reveal_type(Box()) # type is Box[int]
reveal_type(Box(value="Hello World!")) # type is Box[str]
```

New syntax (Python 3.12+):

```python
class Box[T = int]:
def __init__(self, value: T) -> None:
self.value = value

reveal_type(Box()) # type is Box[int]
reveal_type(Box(value="Hello World!")) # type is Box[str]
```

Type variable defaults work with all forms of generics, including classes, functions, and type aliases.
This release completes the implementation by fixing various edge cases involving recursive defaults,
dependencies between type variables, and interactions with variadic generics.

Contributed by Ivan Levkivskyi (PRs [21491](https://github.com/python/mypy/pull/21491),
[21526](https://github.com/python/mypy/pull/21526), [21544](https://github.com/python/mypy/pull/21544)).

### Respect Explicit Return Type of `__new__()`

Mypy now respects explicitly annotated return types in `__new__()` methods. Previously, mypy would
always assume that `__new__()` returns an instance of the current class, ignoring explicit annotations.

With this change, if you explicitly annotate a return type that differs from the implicit type, mypy
will use the explicit annotation:

```python
class Factory:
def __new__(cls) -> Product:
return Product()

reveal_type(Factory()) # type is Product, not Factory
```

Note that mypy still gives an error at the definition site if the explicit annotation is not a
subtype of the current class, since this is technically not type-safe.

For backwards compatibility, there are two exceptions:
- If the return type is `Any`, mypy will still use the current class as the return type.
- If the explicit return type comes from a superclass and is a supertype of the implicit return type,
mypy will use the implicit (more specific) type:

```python
class A:
def __new__(cls) -> A: ...

reveal_type(A()) # type is A

class B:
def __new__(cls) -> B:
return cls()

class C(B): ...
reveal_type(C()) # type is C
```

This fixes several long-standing issues where explicit `__new__()` return types were ignored.

Contributed by Ivan Levkivskyi (PR [21441](https://github.com/python/mypy/pull/21441)).

### TypeForm Support No Longer Experimental

Support for `TypeForm` is no longer experimental. `TypeForm` (introduced in Python 3.14) allows you
to annotate parameters that accept type expressions, providing better type checking for functions
that work with types as values.

```python
from typing import TypeForm

def make_list(tp: TypeForm[T]) -> list[T]:
...

# Correctly typed as list[int]
int_list = make_list(int)
```

`TypeForm` support was previously reverted from mypy 2.1 due to a performance regression, but this
has now been mitigated.

Contributed by Ivan Levkivskyi and Jelle Zijlstra (PRs [21262](https://github.com/python/mypy/pull/21262), [21591](https://github.com/python/mypy/pull/21591),
[21459](https://github.com/python/mypy/pull/21459)).
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### Experimental WASM Wheel for Python 3.14

Mypy now ships an experimental WebAssembly (WASM) wheel for Python 3.14. This allows mypy to run
in WASM environments such as Pyodide and browser-based Python implementations.

The WASM wheel is considered experimental and may have limitations compared to native builds. Please
report any issues you encounter when using mypy in WASM environments.

Contributed by Ivan Levkivskyi (PR [21671](https://github.com/python/mypy/pull/21671)).

### Mypyc Free-threading Improvements

- Make function wrappers thread-safe on free-threaded builds (Jukka Lehtosalo, PR [21620](https://github.com/python/mypy/pull/21620))
- Make list remove and index thread-safe on free-threaded builds (Jukka Lehtosalo, PR [21614](https://github.com/python/mypy/pull/21614))
- Fix dict iteration memory safety on free-threaded builds (Jukka Lehtosalo, PR [21617](https://github.com/python/mypy/pull/21617))
- Make some dict primitives thread-safe on free-threading builds (Jukka Lehtosalo, PR [21616](https://github.com/python/mypy/pull/21616))
- Fix free-threading race condition in argument parsing (Jukka Lehtosalo, PR [21613](https://github.com/python/mypy/pull/21613))
- Document free threading and other doc updates (Jukka Lehtosalo, PR [21494](https://github.com/python/mypy/pull/21494))

### `librt.strings` Updates

- Add `librt.strings.toupper` and `librt.strings.tolower` codepoint primitives (Vaggelis Danias, PR [21553](https://github.com/python/mypy/pull/21553))
- Add `librt.strings.isidentifier` codepoint primitive (Vaggelis Danias, PR [21522](https://github.com/python/mypy/pull/21522))
- Add `librt.strings.isalpha` codepoint primitive (Vaggelis Danias, PR [21521](https://github.com/python/mypy/pull/21521))
- Add `librt.strings.isalnum` codepoint primitive (Vaggelis Danias, PR [21509](https://github.com/python/mypy/pull/21509))
- Add `librt.strings.isdigit` codepoint primitive (Vaggelis Danias, PR [21504](https://github.com/python/mypy/pull/21504))
- Add `librt.strings.isspace` char primitive (Vaggelis Danias, PR [21462](https://github.com/python/mypy/pull/21462))

### Mypyc Improvements

- Fix name lookup when class var and module var have the same name (Jukka Lehtosalo, PR [21594](https://github.com/python/mypy/pull/21594))
- Report file and line number on uncaught exceptions (Jukka Lehtosalo, PR [21584](https://github.com/python/mypy/pull/21584))
- Use `other` arg instead of `self` for RHS type (Ryan Heard, PR [21569](https://github.com/python/mypy/pull/21569))
- Use `method_sig` to get the method signature (Ryan Heard, PR [21567](https://github.com/python/mypy/pull/21567))
- Preserve inherited attribute defaults under `separate=True` (Jo, PR [21547](https://github.com/python/mypy/pull/21547))
- Fix missing cross-group header deps in incremental builds (Jo, PR [21490](https://github.com/python/mypy/pull/21490))
- Fix cross-group call to inherited `__mypyc_defaults_setup` (Jo, PR [21481](https://github.com/python/mypy/pull/21481))
- Fix non-deterministic class struct layout under `separate=True` (Vaggelis Danias, PR [21530](https://github.com/python/mypy/pull/21530))
- Specialize `s[i] == 'x'` to a codepoint int compare (Vaggelis Danias, PR [21579](https://github.com/python/mypy/pull/21579))
- Fix reference leak in mypyc bytes concatenation (Colinxu2020, PR [21469](https://github.com/python/mypy/pull/21469))

### Fixes to Crashes

- Fix crash on invalid recursive variadic alias (Ivan Levkivskyi, PR [21572](https://github.com/python/mypy/pull/21572))
- Fix crashes on variadic unpacking in synthetic types (Ivan Levkivskyi, PR [21555](https://github.com/python/mypy/pull/21555))
- Fix crash on unhandled meet variadic tuple vs instance (Ivan Levkivskyi, PR [21558](https://github.com/python/mypy/pull/21558))
- Fix crash on deferred generic class nested in function (Ivan Levkivskyi, PR [21557](https://github.com/python/mypy/pull/21557))
- Fix crash in new-style type alias with variadic unpack (Ivan Levkivskyi, PR [21551](https://github.com/python/mypy/pull/21551))
- Fix various crashes on recursive type variable defaults (Ivan Levkivskyi, PR [21491](https://github.com/python/mypy/pull/21491))
- Fix crash for empty `Annotated` type application (Rayan Salhab, PR [21503](https://github.com/python/mypy/pull/21503))
- Fix crash on `Unpack` used without arguments in class bases (Sai Asish Y, PR [21470](https://github.com/python/mypy/pull/21470))

### Performance Improvements

- Memoize the options snapshot (Kevin Kannammalil, PR [21354](https://github.com/python/mypy/pull/21354))
- Don't include `not_ready_deps` tracking as relating to mypy internals (Kevin Kannammalil, PR [21389](https://github.com/python/mypy/pull/21389))
- Speed up transitive dependency hash for singleton SCCs (Kevin Kannammalil, PR [21390](https://github.com/python/mypy/pull/21390))
- Optimize typeform checks (Jelle Zijlstra, PR [21459](https://github.com/python/mypy/pull/21459))

### Improvements to the Native Parser

- Support `--shadow-file` with `--native-parser` (Jukka Lehtosalo, PR [21623](https://github.com/python/mypy/pull/21623))
- Add Python version checks to native parser (Kevin Kannammalil, PR [21539](https://github.com/python/mypy/pull/21539))
- Allow nativeparse to parse source code directly (bzoracler, PR [21260](https://github.com/python/mypy/pull/21260))

### Other Notable Fixes and Improvements

- Add function definition notes for `too many positional arguments` errors (Kevin Kannammalil, PR [21410](https://github.com/python/mypy/pull/21410))
- Fix the exportjson tool (.ff cache to .json conversion) (Jukka Lehtosalo, PR [21628](https://github.com/python/mypy/pull/21628))
- Support floats in JSON in fixed-format cache (Ivan Levkivskyi, PR [21603](https://github.com/python/mypy/pull/21603))
- Update `TypedDictType.__init__` signature to preserve backward compat (Jukka Lehtosalo, PR [21590](https://github.com/python/mypy/pull/21590))
- Fix constructor calls for union-bounded `TypeVar`s (Jingchen Ye, PR [21571](https://github.com/python/mypy/pull/21571))
- Fix `TypedDict` indexing with literal keys in comprehensions (Jingchen Ye, PR [21556](https://github.com/python/mypy/pull/21556))
- Correctly handle empty tuple index when unpacked (Ivan Levkivskyi, PR [21545](https://github.com/python/mypy/pull/21545))
- Support protocol checks for self-types in tuple types (Ivan Levkivskyi, PR [21535](https://github.com/python/mypy/pull/21535))
- Fix edge cases in variadic tuple subclasses (Ivan Levkivskyi, PR [21518](https://github.com/python/mypy/pull/21518))
- Special-case constructor for tuple types (Ivan Levkivskyi, PR [21502](https://github.com/python/mypy/pull/21502))
- Fix false positive "Expected TypedDict key to be string literal" for `Union[TypedDict, dict[K, V]]` (Zakir Jiwani, PR [21511](https://github.com/python/mypy/pull/21511))
- Use explicit `Never` for type inference (Ivan Levkivskyi, PR [21497](https://github.com/python/mypy/pull/21497))
- Narrow membership in statically known containers (Shantanu, PR [21461](https://github.com/python/mypy/pull/21461))
- Improve negative narrowing for membership checks on tuples (Shantanu, PR [21456](https://github.com/python/mypy/pull/21456))
- Analyze `TypedDict` decorators (Pranav Manglik, PR [21267](https://github.com/python/mypy/pull/21267))
- Start testing Python 3.15 (Marc Mueller, PR [21439](https://github.com/python/mypy/pull/21439))
- Improved handling of `NamedTuple`, `TypedDict`, `Enum`, and regular classes nested in functions (Ivan Levkivskyi, PR [21478](https://github.com/python/mypy/pull/21478))

### Typeshed Updates

Please see [git log](https://github.com/python/typeshed/commits/main?after=616424285beccaa76f90e87e1e922b1dc68710ca+0&branch=main&path=stdlib) for full list of standard library typeshed stub changes.

### Acknowledgements

Thanks to all mypy contributors who contributed to this release:

- Adam Turner
- alicederyn
- bzoracler
- Colinxu2020
- georgesittas
- Ivan Levkivskyi
- Jelle Zijlstra
- Jingchen Ye
- Jukka Lehtosalo
- Kevin Kannammalil
- lphuc2250gma
- Marc Mueller
- Pranav Manglik
- Rayan Salhab
- Ryan Heard
- Sai Asish Y
- Shantanu
- sobolevn
- Vaggelis Danias
- Victor Letichevsky
- Zakir Jiwani

I'd also like to thank my employer, Dropbox, for supporting mypy development.

## Mypy 2.1

We’ve just uploaded mypy 2.1.0 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)).
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