Remove the need for uses_tagged_union deco

At present we support people adding to the list
of Specs after importing the service. This requires a uses_tagged_union decorator on any
BaseModel that references a Spec. We cannot
currently think of a use case for Specs being implemented outside of scanspec.specs,
so removing this requirement means we can ditch the decorator. It also makes the docs (next PR) easier to write:
- Put your specs in src/scanspec/specs.py
- Release a new version
- Update both blueapi and the scanspec service to use that new version

src/scanspec/core.py

@@ -3,14 +3,7 @@
 from collections.abc import Callable, Iterable, Iterator, Sequence
 from functools import lru_cache
 from inspect import isclass
-from typing import (
-    Any,
-    Generic,
-    Literal,
-    TypeVar,
-    get_origin,
-    get_type_hints,
-)
+from typing import Any, Generic, Literal, TypeVar
 
 import numpy as np
 from pydantic import BaseModel, ConfigDict, Field, GetCoreSchemaHandler
@@ -140,24 +133,6 @@ def get_schema_of_union(cls, source_type: Any, handler: GetCoreSchemaHandler):
     return super_cls
 
 
-def uses_tagged_union(cls_or_func: T) -> T:
-    """
-    T = TypeVar("T", type, Callable)
-        Decorator that processes the type hints of a class or function to detect and
-        register any tagged unions. If a tagged union is detected in the type hints,
-        it registers the class or function as a referrer to that tagged union.
-        Args:
-            cls_or_func (T): The class or function to be processed for tagged unions.
-        Returns:
-            T: The original class or function, unmodified.
-    """
-    for v in get_type_hints(cls_or_func).values():
-        tagged_union = _tagged_unions.get(get_origin(v) or v, None)
-        if tagged_union:
-            tagged_union.add_reference(cls_or_func)
-    return cls_or_func
-
-
 _tagged_unions: dict[type, _TaggedUnion] = {}
 
 
@@ -168,7 +143,6 @@ def __init__(self, base_class: type, discriminator: str):
         self._discriminator = discriminator
         # The members of the tagged union, i.e. subclasses of the baseclass
         self._subclasses: list[type] = []
-        self._references: set[type | Callable] = set()
 
     def add_member(self, cls: type):
         if cls in self._subclasses:
@@ -177,14 +151,8 @@ def add_member(self, cls: type):
         for member in self._subclasses:
             if member is not cls:
                 _TaggedUnion._rebuild(member)
-        for ref in self._references:
-            _TaggedUnion._rebuild(ref)
-
-    def add_reference(self, cls_or_func: type | Callable):
-        self._references.add(cls_or_func)
 
     @staticmethod
-    # https://github.com/bluesky/scanspec/issues/133
     def _rebuild(cls_or_func: type | Callable):
         if isclass(cls_or_func):
             if is_pydantic_dataclass(cls_or_func):
@@ -194,14 +162,14 @@ def _rebuild(cls_or_func: type | Callable):
 
     def schema(self, handler: GetCoreSchemaHandler) -> CoreSchema:
         return tagged_union_schema(
-            make_schema(tuple(self._subclasses), handler),
+            _make_schema(tuple(self._subclasses), handler),
             discriminator=self._discriminator,
             ref=self._base_class.__name__,
         )
 
 
 @lru_cache(1)
-def make_schema(members: tuple[type, ...], handler):
+def _make_schema(members: tuple[type, ...], handler):
     return {member.__name__: handler(member) for member in members}
 
 

src/scanspec/service.py

@@ -10,7 +10,7 @@
 from pydantic import Field
 from pydantic.dataclasses import dataclass
 
-from scanspec.core import AxesPoints, Frames, Path, uses_tagged_union
+from scanspec.core import AxesPoints, Frames, Path
 
 from .specs import Line, Spec
 
@@ -25,7 +25,6 @@
 Points = str | list[float]
 
 
-@uses_tagged_union
 @dataclass
 class ValidResponse:
     """Response model for spec validation."""
@@ -42,7 +41,6 @@ class PointsFormat(str, Enum):
     BASE64_ENCODED = "BASE64_ENCODED"
 
 
-@uses_tagged_union
 @dataclass
 class PointsRequest:
     """A request for generated scan points."""

tests/test_basemodel.py

@@ -1,12 +1,9 @@
 import pytest
 from pydantic import BaseModel, TypeAdapter
-from pydantic.dataclasses import dataclass
 
-from scanspec.core import StrictConfig, uses_tagged_union
 from scanspec.specs import Line, Spec
 
 
-@uses_tagged_union
 class Foo(BaseModel):
     spec: Spec
 
@@ -41,16 +38,3 @@ def test_type_adapter(model: Foo):
     as_json = model.model_dump_json()
     deserialized = type_adapter.validate_json(as_json)
     assert deserialized == model
-
-
-def test_schema_updates_with_new_values():
-    old_schema = TypeAdapter(Foo).json_schema()
-
-    @dataclass(config=StrictConfig)
-    class Splat(Spec[str]):  # NOSONAR
-        def axes(self) -> list[str]:
-            return ["*"]
-
-    new_schema = TypeAdapter(Foo).json_schema()
-
-    assert new_schema != old_schema