Some changelog updates for 2.0

CHANGELOG.md

@@ -2,44 +2,114 @@
 
 ## Next Release
 
-### Enabling `--local-partial-types` by default
+### Enabling `--local-partial-types` by Default
 
 This flag affects the inference of types based on assignments in other scopes.
 For now, explicitly disabling this continues to be supported, but this support will be removed
 in the future as the legacy behaviour is hard to support with other current and future features
 in mypy, like the daemon or the new implementation of flexible redefinitions.
 
-Contributed by Ivan Levkivskyi, Jukka Lehtosalo, Shantanu in [PR 21163](https://github.com/python/mypy/pull/21163)
+Contributed by Ivan Levkivskyi, Jukka Lehtosalo, Shantanu in [PR 21163](https://github.com/python/mypy/pull/21163).
 
-### Enabling `--strict-bytes` by default
+### Enabling `--strict-bytes` by Default
 
 Per [PEP 688](https://peps.python.org/pep-0688), mypy no longer treats `bytearray` and `memoryview`
 values as assignable to the `bytes` type.
 
-Contributed by Shantanu in [PR 18371](https://github.com/python/mypy/pull/18371)
+Contributed by Shantanu in [PR 18371](https://github.com/python/mypy/pull/18371).
+
+### New Behavior for `--allow-redefinition`
+
+The `--allow-redefinition` flag now behaves like `--allow-redefinition-new` in mypy 1.20
+and earlier. The new behavior is generally more flexible. For example, you can have different
+types for a variable in different blocks:
+
+```python
+# mypy: allow-redefinition
+
+def foo(cond: bool) -> None:
+    if cond:
+        for x in ["a", "b"]:
+            # Type of "x" is "str" here
+            ...
+    else:
+        for x in [1, 2]:
+            # Type of "x" is "int" here
+            ...
+```
+
+The new behavior requires `--local-partial-types`, which is now enabled by default.
+
+However, `--allow-redefinition` doesn't allow giving two type annotations for the same
+variable. The old behavior (sometimes) allows this. Code like this now generates an error
+when using `--allow-redefinition`:
+
+```python
+def foo() -> None:
+    x: list[int] = []
+    ...
+    x: list[str] = []  # Error: "x" redefined
+    ...
+```
+
+You can still use `--allow-redefinition-old` to fall back to the old behavior. We have no
+plans to remove the legacy behavior, but the old functionality is maintained on a best effort
+basis.
+
+Contributed by Jukka Lehtosalo in [PR 21276](https://github.com/python/mypy/pull/21276).
+
+### Parallel Type Checking
+
+Mypy now supports experimental parallel and incremental type checking. Use `--num-workers N`
+or `-nN` to use `N` worker processes to type check in parallel. The speedup depends on the
+import structure of your codebase and your environment, but for large projects we've seen
+performance gains of **up to 5x** when using 8 worker processes.
+
+Parallel type checking implicitly enables the new native parser. There are still some
+minor semantic differences between parallel and non-parallel modes, which we will be fixing
+in future mypy releases.
+
+Contributed by Ivan Levkivskyi, with additional contributions from Emma Smith and Jukka
+Lehtosalo.
 
 ### Drop Support for Targeting Python 3.9
 
 Mypy no longer supports type checking code with `--python-version 3.9`.
 Use `--python-version 3.10` or newer.
 
-Contributed by Shantanu, Marc Mueller in [PR 21243](https://github.com/python/mypy/pull/21243)
+Contributed by Shantanu, Marc Mueller in [PR 21243](https://github.com/python/mypy/pull/21243).
 
-### Remove special casing of legacy bundled stubs
+### Remove Special Casing of Legacy Bundled Stubs
 
 Mypy used to bundle stubs for a few packages in versions 0.812 and earlier. To navigate the
 transition, mypy used to report missing types for these packages even if `--ignore-missing-imports`
 was set. Mypy now consistently respects `--ignore-missing-imports` for all packages.
 
-Contributed by Shantanu in [PR 18372](https://github.com/python/mypy/pull/18372)
+Contributed by Shantanu in [PR 18372](https://github.com/python/mypy/pull/18372).
 
-### Prevent assignment to None for non-Optional class variables with type comments
+### Prevent Assignment to None for Non-Optional Class Variables with Type Comments
 
 Mypy used to allow assignment to None for class variables when using type comments. This was a
 common idiom in Python 3.5 and earlier, prior to the introduction of variable annotations.
 However, this was a soundness hole and has now been removed.
 
-Contributed by Shantanu in [PR 20054](https://github.com/python/mypy/pull/20054)
+Contributed by Shantanu in [PR 20054](https://github.com/python/mypy/pull/20054).
+
+### librt.strings: String and Bytes Primitives for Mypyc
+
+In mypy 1.20, we introduced [librt](https://pypi.org/project/librt/) as a standard library
+for mypyc that fills in some gaps in the Python standard library and the C API.
+This release adds the new module `librt.strings`, which contains utilities for building
+string and bytes objects, and for accessing and generating binary data:
+
+ * `StringWriter` and `BytesWriter` classes allow quickly building `str` and `bytes` objects
+   from parts.
+ * `read_*` and `write_*` functions provide fast reading and writing of binary-encoded data.
+
+Refer to the [documentation](https://mypyc.readthedocs.io/en/latest/librt_strings.html) for
+the details.
+
+Contributed by Jukka Lehtosalo.
 
 ## Mypy 1.20