Repository: jcrist/msgspec (python)

Issue:
TypeError from inspect.type_info with unhashable Annotated metadata
### Description

## MCVE

```py
from typing import Annotated

import msgspec


class Test(msgspec.Struct):
    a: Annotated[int, {"unhashable": "metadata"}]


t = Test(a=1)

print(t.a)  # 1 (no runtime issues)

msgspec.inspect.type_info(Test)  # TypeError: unhashable type: 'dict'
 
```

## Error

```
 Traceback (most recent call last):
  File "/home/peter/PycharmProjects/msgspec-mcve/main.py", line 14, in <module>
    msgspec.inspect.type_info(Test)
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 614, in type_info
    return multi_type_info([type])[0]
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 580, in multi_type_info
    return _Translator(types).run()
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 721, in run
    return tuple(self.translate(t) for t in self.types)
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 721, in <genexpr>
    return tuple(self.translate(t) for t in self.types)
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 755, in translate
    out = self._translate_inner(t, args, **constrs)
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 903, in _translate_inner
    type=self.translate(hints[name]),
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 724, in translate
    t, args, metadata = _origin_args_metadata(typ)
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 622, in _origin_args_metadata
    origin = _CONCRETE_TYPES.get(t)
  File "/usr/lib/python3.10/typing.py", line 1651, in __hash__
    return hash((self.__origin__, self.__metadata__))
TypeError: unhashable type: 'dict'
```

There doesn't seem to be any hard requirement that type metadata via `Annotated` must be hashable (searching for "hash" in [pep 593](https://peps.python.org/pep-0593/) doesn't yield anything), however, the implementation of `_AnnotatedAlias.__hash__()` does hash any metadata as well as the origin type ([ref](https://github.com/python/cpython/blob/1556f426da3f2fb5842689999933c8038b65c034/Lib/typing.py#L1983-L1985)):

```py
    def __hash__(self):
        return hash((self.__origin__, self.__metadata__))
```


Pull request description:
Handle where `Annotated` has unhashable metadata.
This PR handles the case where `t` in the call to  `_CONCRETE_TYPES.get(t)` is not hashable, such as when an `Annotated` instance contains unhashable metadata.

Closes #565

Patch:
diff --git a/msgspec/inspect.py b/msgspec/inspect.py
index d782018..df8d2c0 100644
--- a/msgspec/inspect.py
+++ b/msgspec/inspect.py
@@ -619,7 +619,12 @@ def _origin_args_metadata(t):
     # Strip wrappers (Annotated, NewType, Final) until we hit a concrete type
     metadata = []
     while True:
-        origin = _CONCRETE_TYPES.get(t)
+        try:
+            origin = _CONCRETE_TYPES.get(t)
+        except TypeError:
+            # t is not hashable
+            origin = None
+
         if origin is not None:
             args = None
             break


Test patch:
diff --git a/tests/test_inspect.py b/tests/test_inspect.py
index e1c9dc0..cd83040 100644
--- a/tests/test_inspect.py
+++ b/tests/test_inspect.py
@@ -765,6 +765,13 @@ def test_metadata():
     )
 
 
+def test_inspect_with_unhashable_metadata():
+
+    typ = Annotated[int, {"unhashable"}]
+
+    assert mi.type_info(typ) == mi.IntType()
+
+
 def test_multi_type_info():
     class Example(msgspec.Struct):
         x: int