Fix annotations support on 3.14 (#852)

Author: JelleZijlstra

msgspec/_core.c

@@ -452,6 +452,7 @@ typedef struct {
 #endif
     PyObject *astimezone;
     PyObject *re_compile;
+    PyObject *get_annotate_from_class_namespace;
     uint8_t gc_cycle;
 } MsgspecState;
 
@@ -5814,12 +5815,45 @@ structmeta_is_classvar(
 
 static int
 structmeta_collect_fields(StructMetaInfo *info, MsgspecState *mod, bool kwonly) {
-    PyObject *annotations = PyDict_GetItemString(
+    PyObject *annotations = PyDict_GetItemString(  // borrowed reference
         info->namespace, "__annotations__"
     );
-    if (annotations == NULL) return 0;
+    if (annotations == NULL) {
+        if (mod->get_annotate_from_class_namespace != NULL) {
+            PyObject *annotate = PyObject_CallOneArg(
+                mod->get_annotate_from_class_namespace, info->namespace
+            );
+            if (annotate == NULL) {
+                return -1;
+            }
+            if (annotate == Py_None) {
+                Py_DECREF(annotate);
+                return 0;
+            }
+            PyObject *format = PyLong_FromLong(1);  /* annotationlib.Format.VALUE */
+            if (format == NULL) {
+                Py_DECREF(annotate);
+                return -1;
+            }
+            annotations = PyObject_CallOneArg(
+                annotate, format
+            );
+            Py_DECREF(annotate);
+            Py_DECREF(format);
+            if (annotations == NULL) {
+                return -1;
+            }
+        }
+        else {
+            return 0;  // No annotations, nothing to do
+        }
+    }
+    else {
+        Py_INCREF(annotations);
+    }
 
     if (!PyDict_Check(annotations)) {
+        Py_DECREF(annotations);
         PyErr_SetString(PyExc_TypeError, "__annotations__ must be a dict");
         return -1;
     }
@@ -5869,6 +5903,7 @@ structmeta_collect_fields(StructMetaInfo *info, MsgspecState *mod, bool kwonly)
     }
     return 0;
 error:
+    Py_DECREF(annotations);
     Py_XDECREF(module_ns);
     return -1;
 }
@@ -22225,6 +22260,26 @@ PyInit__core(void)
     Py_DECREF(temp_module);
     if (st->re_compile == NULL) return NULL;
 
+    /* annotationlib.get_annotate_from_class_namespace */
+    temp_module = PyImport_ImportModule("annotationlib");
+    if (temp_module == NULL) {
+        if (PyErr_ExceptionMatches(PyExc_ModuleNotFoundError)) {
+            // Below Python 3.14
+            PyErr_Clear();
+            st->get_annotate_from_class_namespace = NULL;
+        }
+        else {
+            return NULL;
+        }
+    }
+    else {
+        st->get_annotate_from_class_namespace = PyObject_GetAttrString(
+            temp_module, "get_annotate_from_class_namespace"
+        );
+        Py_DECREF(temp_module);
+        if (st->get_annotate_from_class_namespace == NULL) return NULL;
+    }
+
     /* Initialize cached constant strings */
 #define CACHED_STRING(attr, str) \
     if ((st->attr = PyUnicode_InternFromString(str)) == NULL) return NULL

msgspec/_utils.py

@@ -1,5 +1,6 @@
 # type: ignore
 import collections
+import inspect
 import sys
 import typing
 
@@ -71,6 +72,13 @@ def _eval_type(t, globalns, localns):
     _eval_type = typing._eval_type
 
 
+if sys.version_info >= (3, 10):
+    from inspect import get_annotations as _get_class_annotations
+else:
+    def _get_class_annotations(cls):
+        return cls.__dict__.get("__annotations__", {})
+
+
 def _apply_params(obj, mapping):
     if isinstance(obj, typing.TypeVar):
         return mapping.get(obj, obj)
@@ -149,17 +157,17 @@ def get_class_annotations(obj):
         cls_locals = dict(vars(cls))
         cls_globals = getattr(sys.modules.get(cls.__module__, None), "__dict__", {})
 
-        ann = cls.__dict__.get("__annotations__", {})
+        ann = _get_class_annotations(cls)
         for name, value in ann.items():
             if name in hints:
                 continue
-            if value is None:
-                value = type(None)
-            elif isinstance(value, str):
+            if isinstance(value, str):
                 value = _forward_ref(value)
             value = _eval_type(value, cls_locals, cls_globals)
             if mapping is not None:
                 value = _apply_params(value, mapping)
+            if value is None:
+                value = type(None)
             hints[name] = value
     return hints