Call __post_init__ when converting struct from object

Previously a struct's `__post_init__` method wouldn't be called when
converting from a custom mapping or object with `from_attributes=True`.
This PR fixes that and expands the tests to cover this case.

msgspec/_core.c

@@ -21364,6 +21364,9 @@ convert_object_to_struct(
  should_untrack = !MS_MAYBE_TRACKED(val);
  }
  }
+
+ if (Struct_decode_post_init(struct_type, out, path) < 0) goto error;
+
  Py_LeaveRecursiveCall();
  if (is_gc && !should_untrack)
  PyObject_GC_Track(out);

tests/test_convert.py

@@ -2239,18 +2239,18 @@ class Test2(Struct, Generic[T], tag=True, array_like=array_like):
 
 
 class TestStructPostInit:
- @pytest.mark.parametrize("array_like", [False, True])
  @pytest.mark.parametrize("union", [False, True])
- def test_struct_post_init(self, array_like, union):
- count = 0
+ @mapcls_from_attributes_and_array_like
+ def test_struct_post_init(self, union, mapcls, from_attributes, array_like):
+ called = False
  singleton = object()
 
  class Ex(Struct, array_like=array_like, tag=union):
  x: int
 
  def __post_init__(self):
- nonlocal count
- count += 1
+ nonlocal called
+ called = True
  return singleton
 
  if union:
@@ -2262,25 +2262,23 @@ class Ex2(Struct, array_like=array_like, tag=True):
  else:
  typ = Ex
 
- msg = Ex(1)
- buf = to_builtins(msg)
- res = convert(buf, type=typ)
- assert res == msg
- assert count == 2 # 1 for Ex(), 1 for decode
+ msg = mapcls(type="Ex", x=1) if union else mapcls(x=1)
+ res = convert(msg, type=typ, from_attributes=from_attributes)
+ assert type(res) is Ex
+ assert called
  assert sys.getrefcount(singleton) == 2 # 1 for ref, 1 for call
 
- @pytest.mark.parametrize("array_like", [False, True])
  @pytest.mark.parametrize("union", [False, True])
  @pytest.mark.parametrize("exc_class", [ValueError, TypeError, OSError])
- def test_struct_post_init_errors(self, array_like, union, exc_class):
- error = False
-
+ @mapcls_from_attributes_and_array_like
+ def test_struct_post_init_errors(
+ self, union, exc_class, mapcls, from_attributes, array_like
+ ):
  class Ex(Struct, array_like=array_like, tag=union):
  x: int
 
  def __post_init__(self):
- if error:
- raise exc_class("Oh no!")
+ raise exc_class("Oh no!")
 
  if union:
 
@@ -2291,16 +2289,15 @@ class Ex2(Struct, array_like=array_like, tag=True):
  else:
  typ = Ex
 
- msg = to_builtins([Ex(1)])
- error = True
+ msg = [mapcls(type="Ex", x=1) if union else mapcls(x=1)]
 
  if exc_class in (ValueError, TypeError):
  expected = ValidationError
  else:
  expected = exc_class
 
  with pytest.raises(expected, match="Oh no!") as rec:
- convert(msg, type=List[typ])
+ convert(msg, type=List[typ], from_attributes=from_attributes)
 
  if expected is ValidationError:
  assert "- at `$[0]`" in str(rec.value)