tenseleyflow/sway / ac3f2ff

Browse files

sway(backends): custom entry-point dispatch with protocol validation

Authored by espadonne
SHA
ac3f2ff40004e551199966391b1876b9e5f67e20
Parents
c666cbf
Tree
d64360e

2 changed files

StatusFile+-
M src/dlm_sway/backends/__init__.py 53 5
M tests/unit/test_backend_registry.py 82 3
src/dlm_sway/backends/__init__.pymodified
@@ -55,13 +55,61 @@ def build(base_spec: ModelSpec, *, adapter_path: Path | None = None) -> Differen
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         )
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     if base_spec.kind == "custom":
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-        raise BackendNotAvailableError(
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-            "custom",
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-            extra="hf",
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-            hint="Custom backend entry-point dispatch shipping in a later milestone.",
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-        )
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+        return _load_custom(base_spec, effective_adapter)
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     raise SpecValidationError(f"unknown backend kind: {base_spec.kind!r}")
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+def _load_custom(base_spec: ModelSpec, adapter: Path | None) -> DifferentialBackend:
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+    """Dispatch to a user-supplied backend via ``entry_point='pkg.mod:Name'``.
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+
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+    The imported class is instantiated as ``Cls(base_spec=..., adapter_path=...)``
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+    — the same signature as :class:`dlm_sway.backends.hf.HuggingFaceDifferentialBackend`
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+    so authors can model their implementation on the built-in. The
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+    result is runtime-checked against :class:`DifferentialBackend` so
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+    protocol violations fail at construction, not deep inside a probe.
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+    """
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+    from dlm_sway.core.scoring import DifferentialBackend as DiffBackend
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+
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+    entry = base_spec.entry_point
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+    if not entry:
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+        raise SpecValidationError(
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+            "kind='custom' requires an entry_point of the form 'pkg.module:ClassName'"
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+        )
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+    if ":" not in entry:
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+        raise SpecValidationError(f"entry_point must be 'pkg.module:ClassName', got {entry!r}")
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+    module_path, _, class_name = entry.partition(":")
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+    if not module_path or not class_name:
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+        raise SpecValidationError(f"entry_point must be 'pkg.module:ClassName', got {entry!r}")
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+
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+    import importlib
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+
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+    try:
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+        module = importlib.import_module(module_path)
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+    except ImportError as exc:
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+        raise SpecValidationError(
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+            f"custom backend: cannot import module {module_path!r}: {exc}"
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+        ) from exc
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+    cls = getattr(module, class_name, None)
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+    if cls is None:
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+        raise SpecValidationError(
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+            f"custom backend: module {module_path!r} has no attribute {class_name!r}"
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+        )
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+
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+    try:
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+        instance = cls(base_spec=base_spec, adapter_path=adapter)
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+    except TypeError as exc:
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+        raise SpecValidationError(
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+            f"custom backend {entry!r} constructor signature mismatch: {exc}. "
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+            "Expected Cls(base_spec: ModelSpec, adapter_path: Path | None)"
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+        ) from exc
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+
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+    if not isinstance(instance, DiffBackend):
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+        raise SpecValidationError(
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+            f"custom backend {entry!r} does not satisfy DifferentialBackend "
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+            "(needs as_base() and as_finetuned() context managers)"
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+        )
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+    return instance
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+
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+
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 __all__ = ["build"]
tests/unit/test_backend_registry.pymodified
@@ -31,13 +31,92 @@ class TestRegistry:
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             build(ModelSpec(base="x", kind="mlx", adapter=Path("/tmp/a")))
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         assert exc_info.value.backend == "mlx"
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-    def test_custom_not_yet_available(self) -> None:
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-        with pytest.raises(BackendNotAvailableError):
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+    def test_custom_requires_entry_point(self) -> None:
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+        with pytest.raises(SpecValidationError, match="entry_point"):
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+            build(ModelSpec(base="x", kind="custom", adapter=Path("/tmp/a")))
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+
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+    def test_custom_validates_entry_point_shape(self) -> None:
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+        with pytest.raises(SpecValidationError, match="pkg.module:ClassName"):
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+            build(
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+                ModelSpec(
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+                    base="x",
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+                    kind="custom",
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+                    entry_point="not_a_valid_entry_point",
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+                    adapter=Path("/tmp/a"),
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+                )
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+            )
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+
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+    def test_custom_rejects_unimportable_module(self) -> None:
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+        with pytest.raises(SpecValidationError, match="cannot import"):
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             build(
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                 ModelSpec(
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                     base="x",
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                     kind="custom",
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-                    entry_point="pkg:Backend",
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+                    entry_point="nonexistent_pkg_xyz:Backend",
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                     adapter=Path("/tmp/a"),
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                 )
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             )
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+
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+    def test_custom_rejects_missing_class(self) -> None:
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+        with pytest.raises(SpecValidationError, match="has no attribute"):
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+            build(
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+                ModelSpec(
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+                    base="x",
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+                    kind="custom",
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+                    entry_point="dlm_sway:NoSuchClass",
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+                    adapter=Path("/tmp/a"),
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+                )
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+            )
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+
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+    def test_custom_rejects_non_differential_class(self) -> None:
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+        # A class that accepts the canonical constructor args but doesn't
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+        # implement the protocol.
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+        import sys
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+        import types
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+
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+        class _Bad:
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+            def __init__(self, base_spec, adapter_path):  # type: ignore[no-untyped-def]
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+                del base_spec, adapter_path
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+
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+        mod = types.ModuleType("_sway_bad_mod")
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+        mod.Bad = _Bad  # type: ignore[attr-defined]
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+        sys.modules["_sway_bad_mod"] = mod
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+
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+        with pytest.raises(SpecValidationError, match="DifferentialBackend"):
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+            build(
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+                ModelSpec(
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+                    base="x",
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+                    kind="custom",
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+                    entry_point="_sway_bad_mod:Bad",
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+                    adapter=Path("/tmp/a"),
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+                )
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+            )
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+
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+    def test_custom_dispatches_to_valid_backend(self) -> None:
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+        # Use the dummy backend via a custom entry point. The dummy class's
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+        # __init__ takes different args, so we write a thin adapter class.
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+        from dlm_sway.backends.dummy import DummyDifferentialBackend, DummyResponses
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+
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+        class _AdapterBackend(DummyDifferentialBackend):
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+            def __init__(self, base_spec, adapter_path):  # type: ignore[no-untyped-def]
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+                super().__init__(base=DummyResponses(), ft=DummyResponses())
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+
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+        # Register on a throwaway module we can find by name.
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+        import sys
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+        import types
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+
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+        mod = types.ModuleType("_sway_custom_test_mod")
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+        mod.AdapterBackend = _AdapterBackend  # type: ignore[attr-defined]
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+        sys.modules["_sway_custom_test_mod"] = mod
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+
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+        backend = build(
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+            ModelSpec(
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+                base="x",
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+                kind="custom",
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+                entry_point="_sway_custom_test_mod:AdapterBackend",
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+                adapter=Path("/tmp/a"),
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+            )
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+        )
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+        from dlm_sway.core.scoring import DifferentialBackend
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+
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+        assert isinstance(backend, DifferentialBackend)