From b8578e243055b6c29c5f3996a39f2389919fed83 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tin=20Tvrtkovi=C4=87?= <tinchester@gmail.com>
Date: Fri, 12 Jan 2024 00:45:59 +0100
Subject: [PATCH] More msgspec work

---
 docs/preconf.md                       | 17 +++++++++++++++++
 src/cattrs/preconf/msgspec.py         |  7 +++++++
 tests/preconf/test_msgspec_cpython.py |  6 ++++++
 3 files changed, 30 insertions(+)

diff --git a/docs/preconf.md b/docs/preconf.md
index 4abe7352..a6ce06a3 100644
--- a/docs/preconf.md
+++ b/docs/preconf.md
@@ -92,6 +92,23 @@ Compatibility notes:
 - _attrs_ classes, dataclasses and sequences are handled directly by _msgspec_ if possible, otherwise by the normal _cattrs_ machinery.
 This means it's possible the validation errors produced may be _msgspec_ validation errors instead of _cattrs_ validation errors.
 
+This converter supports {meth}`get_loads_hook() <cattrs.preconf.msgspec.MsgspecJsonConverter.get_loads_hook>` and {meth}`get_dumps_hook() <cattrs.preconf.msgspec.MsgspecJsonConverter.get_loads_hook>`.
+These are factories for dumping and loading functions (as opposed to unstructuring and structuring); the hooks returned by this may be further optimized to offload as much work as possible to _msgspec_.
+
+```python
+>>> from cattrs.preconf.msgspec import make_converter
+
+>>> @define
+... class Test:
+...     a: int
+
+>>> converter = make_converter()
+>>> dumps = converter.get_dumps_hook(A)
+
+>>> dumps(Test(1))  # Will use msgspec directly.
+b'{"a":1}'
+```
+
 _msgspec_ doesn't support PyPy.
 
 ```{versionadded} 24.1.0
diff --git a/src/cattrs/preconf/msgspec.py b/src/cattrs/preconf/msgspec.py
index 364b73be..1dd3edd1 100644
--- a/src/cattrs/preconf/msgspec.py
+++ b/src/cattrs/preconf/msgspec.py
@@ -3,6 +3,7 @@
 
 from base64 import b64decode
 from datetime import date, datetime
+from functools import partial
 from typing import Any, Callable, TypeVar, Union
 
 from attrs import has as attrs_has
@@ -24,6 +25,8 @@
 
 
 class MsgspecJsonConverter(Converter):
+    """A converter specialized for the _msgspec_ library."""
+
     #: The msgspec encoder for dumping.
     encoder: Encoder = Encoder()
 
@@ -46,6 +49,10 @@ def loads(self, data: bytes, cl: type[T], **kwargs: Any) -> T:
         """Decode and structure `cl` from the provided JSON bytes."""
         return self.structure(decode(data, **kwargs), cl)
 
+    def get_loads_hook(self, cl: type[T]) -> Callable[[bytes], T]:
+        """Produce a `loads` hook for the given type."""
+        return partial(self.loads, cl=cl)
+
 
 def configure_converter(converter: Converter) -> None:
     """Configure the converter for the msgspec library.
diff --git a/tests/preconf/test_msgspec_cpython.py b/tests/preconf/test_msgspec_cpython.py
index aaa59cc6..19a9add4 100644
--- a/tests/preconf/test_msgspec_cpython.py
+++ b/tests/preconf/test_msgspec_cpython.py
@@ -53,6 +53,12 @@ def test_dump_hook_attrs(converter: Conv):
     assert converter.get_dumps_hook(A) == converter.encoder.encode
 
 
+def test_get_loads_hook(converter: Conv):
+    """`Converter.get_loads_hook` works."""
+    hook = converter.get_loads_hook(A)
+    assert hook(b'{"a": 1}') == A(1)
+
+
 def test_basic_structs(converter: Conv):
     """Handling msgspec structs works."""