core: gracefully reject unsupported annotations

src/cachew/__init__.py

@@ -31,7 +31,7 @@ def orjson_dumps(*args: Any, **kwargs: Any) -> bytes:  # type: ignore[misc]
         # sqlite needs a blob
         return json.dumps(*args, **kwargs).encode('utf8')
 
-    orjson_loads = json.loads  # type: ignore[assignment]  # ty: ignore[invalid-assignment]
+    orjson_loads = json.loads  # type: ignore[assignment]
 
 import platformdirs
 

src/cachew/marshall/cachew.py

@@ -377,15 +377,16 @@ def build_schema(Type) -> Schema:
     if is_dictish:
         (ft, tt) = args
         fts = build_schema(ft)
+        if not isinstance(fts, SPrimitive):
+            raise TypeNotSupported(type_=Type, reason='dictionary key type must be primitive')
         tts = build_schema(tt)
-        assert isinstance(fts, SPrimitive)
         return SDict(
             type=origin,
             ft=fts,
             tt=tts,
         )
 
-    raise RuntimeError(f"unsupported: {Type=} {origin=} {args=}")
+    raise TypeNotSupported(type_=Type, reason=f'generic type with origin {origin} is unsupported')
 
 
 ######### tests

src/cachew/tests/test_cachew.py

@@ -307,6 +307,38 @@ def fun2() -> Iterable[UGood | UBad]:
             yield UGood(x=2)
 
 
+def test_unsupported_annotation_follows_error_policy(
+    *,
+    tmp_path: Path,
+    restore_settings,
+) -> None:
+    """
+    Unsupported annotations must not bypass Cachew's strict or defensive setup policy.
+    Strict mode must reject decoration without running the source, while defensive mode must return the original function and leave it uncached.
+    """
+
+    source_calls = 0
+
+    def source() -> Iterator[Callable[[int], str]]:
+        nonlocal source_calls
+        source_calls += 1
+        yield str
+
+    cache_path = tmp_path / 'cache'
+    settings.THROW_ON_ERROR = True
+    with pytest.raises(CachewException, match='failed to infer cache type'):
+        cachew(cache_path=cache_path)(source)
+    assert source_calls == 0
+
+    settings.THROW_ON_ERROR = False
+    decorated = cachew(cache_path=cache_path)(source)
+    assert decorated is source
+    assert list(decorated()) == [str]
+    assert list(decorated()) == [str]
+    assert source_calls == 2
+    assert cache_path.exists() is False
+
+
 class BB(NamedTuple):
     xx: int
     yy: int