fix: prevent FastStream bootstrap NameError when optional extras are missing

lite_bootstrap/bootstrappers/base.py

@@ -42,14 +42,18 @@ def __init__(self, bootstrap_config: BaseConfig) -> None:
                 self.instruments.append(instrument)
 
     def _register_or_skip(self, instrument_type: type[BaseInstrument]) -> BaseInstrument | None:
-        instrument = instrument_type(bootstrap_config=self.bootstrap_config)
-        if not instrument.check_dependencies():
+        # Check dependencies before instantiation: an instrument's __init__
+        # may reference symbols gated behind an optional import (e.g. a
+        # default_factory that calls into the missing package), which would
+        # raise NameError before the check_dependencies skip could run.
+        if not instrument_type.check_dependencies():
             warnings.warn(
-                instrument.missing_dependency_message,
+                instrument_type.missing_dependency_message,
                 category=InstrumentDependencyMissingWarning,
                 stacklevel=4,
             )
             return None
+        instrument = instrument_type(bootstrap_config=self.bootstrap_config)
         if not instrument.is_ready():
             warnings.warn(
                 f"{instrument_type.__name__} is not ready: {instrument.not_ready_message}",

lite_bootstrap/bootstrappers/faststream_bootstrapper.py

@@ -87,7 +87,10 @@ async def check_health(_: object) -> "AsgiResponse":
                 else AsgiResponse(b"Service is unhealthy", 500, headers={"content-type": "text/plain"})
             )
 
-        if self.bootstrap_config.opentelemetry_generate_health_check_spans:
+        if (
+            self.bootstrap_config.opentelemetry_generate_health_check_spans
+            and import_checker.is_opentelemetry_installed
+        ):
             check_health = tracer.start_as_current_span(f"GET {self.bootstrap_config.health_checks_path}")(
                 check_health,
             )

tests/conftest.py

@@ -58,3 +58,39 @@ def emulate_package_missing(package_name: str) -> typing.Iterator[None]:
     finally:
         sys.modules[package_name] = old_module
         reload(import_checker)
+
+
+@contextlib.contextmanager
+def emulate_package_missing_with_module_reload(
+    package_name: str, module_names: typing.Iterable[str]
+) -> typing.Iterator[None]:
+    # Reload listed modules under emulate_package_missing so their
+    # `if import_checker.is_X_installed: import X` blocks re-evaluate against
+    # the patched flag. `importlib.reload` preserves existing module globals,
+    # so we wipe non-dunder names first to truly simulate a fresh import where
+    # the conditional import never ran.
+    module_names = list(module_names)
+    snapshots: dict[str, dict[str, typing.Any]] = {}
+    for name in module_names:
+        if name in sys.modules:
+            snapshots[name] = dict(sys.modules[name].__dict__)
+
+    def _wipe_and_reload() -> None:
+        for name in module_names:
+            if name in sys.modules:
+                mod_dict = sys.modules[name].__dict__
+                for key in [k for k in mod_dict if not k.startswith("__")]:
+                    del mod_dict[key]
+                reload(sys.modules[name])
+
+    with emulate_package_missing(package_name):
+        _wipe_and_reload()
+        try:
+            yield
+        finally:
+            for name, snap in snapshots.items():
+                if name in sys.modules:
+                    mod_dict = sys.modules[name].__dict__
+                    for key in [k for k in mod_dict if not k.startswith("__")]:
+                        del mod_dict[key]
+                    mod_dict.update({k: v for k, v in snap.items() if not k.startswith("__")})

tests/test_faststream_bootstrap.py

@@ -13,7 +13,12 @@
 from starlette.testclient import TestClient
 
 from lite_bootstrap import FastStreamBootstrapper, FastStreamConfig
-from tests.conftest import CustomInstrumentor, SentryTestTransport, emulate_package_missing
+from tests.conftest import (
+    CustomInstrumentor,
+    SentryTestTransport,
+    emulate_package_missing,
+    emulate_package_missing_with_module_reload,
+)
 
 
 logger = structlog.getLogger(__name__)
@@ -127,3 +132,30 @@ def test_faststream_bootstrapper_with_missing_instrument_dependency(broker: Redi
     bootstrap_config = build_faststream_config(broker=broker)
     with emulate_package_missing(package_name), pytest.warns(UserWarning, match=package_name):
         FastStreamBootstrapper(bootstrap_config=bootstrap_config)
+
+
+def test_faststream_bootstrap_without_prometheus_client(broker: RedisBroker) -> None:
+    # Regression: issue #87 bug 1 — FastStreamPrometheusInstrument's
+    # default_factory called prometheus_client.CollectorRegistry() during
+    # dataclass __init__, raising NameError before check_dependencies() ran.
+    bootstrap_config = build_faststream_config(broker=broker)
+    with emulate_package_missing_with_module_reload(
+        "prometheus_client",
+        ["lite_bootstrap.bootstrappers.faststream_bootstrapper"],
+    ):
+        with pytest.warns(UserWarning, match="prometheus_client"):
+            bootstrapper = FastStreamBootstrapper(bootstrap_config=bootstrap_config)
+        bootstrapper.bootstrap()
+
+
+def test_faststream_bootstrap_without_opentelemetry(broker: RedisBroker) -> None:
+    # Regression: issue #87 bug 2 — FastStreamHealthChecksInstrument.bootstrap
+    # referenced unbound `tracer` when opentelemetry was absent and
+    # opentelemetry_generate_health_check_spans defaulted to True.
+    bootstrap_config = build_faststream_config(broker=broker)
+    with emulate_package_missing_with_module_reload(
+        "opentelemetry",
+        ["lite_bootstrap.bootstrappers.faststream_bootstrapper"],
+    ):
+        bootstrapper = FastStreamBootstrapper(bootstrap_config=bootstrap_config)
+        bootstrapper.bootstrap()