chore: Make start_span fail if unsupported args are provided

MIGRATION_GUIDE.md

@@ -131,7 +131,6 @@ Looking to upgrade from Sentry SDK 2.x to 3.x? Here's a comprehensive list of wh
 
 ### Removed
 
-- Spans no longer have a `description`. Use `name` instead.
 - Dropped support for Python 3.6.
 - The `enable_tracing` `init` option has been removed. Configure `traces_sample_rate` directly.
 - The `propagate_traces` `init` option has been removed. Use `trace_propagation_targets` instead.
@@ -157,11 +156,15 @@ Looking to upgrade from Sentry SDK 2.x to 3.x? Here's a comprehensive list of wh
 - `profiles_sample_rate` and `profiler_mode` were removed from options available via `_experiments`. Use the top-level `profiles_sample_rate` and `profiler_mode` options instead.
 - `Transport.capture_event` has been removed. Use `Transport.capture_envelope` instead.
 - Function transports are no longer supported. Subclass the `Transport` instead.
+- `start_transaction` (`start_span`) no longer takes the following arguments:
+  - `trace_id`, `baggage`: use `continue_trace` for propagation from headers or environment variables
+  - `same_process_as_parent`
+  - `span_id`
+  - `parent_span_id`: you can supply a `parent_span` instead
 - Setting `Scope.transaction` directly is no longer supported. Use `Scope.set_transaction_name()` instead.
 - Passing a list or `None` for `failed_request_status_codes` in the Starlette integration is no longer supported. Pass a set of integers instead.
 - The `span` argument of `Scope.trace_propagation_meta` is no longer supported.
 - Setting `Scope.user` directly is no longer supported. Use `Scope.set_user()` instead.
-- `start_transaction` (`start_span`) no longer takes a `baggage` argument. Use the `continue_trace()` context manager instead to propagate baggage.
 - Dropped support for Django versions below 2.0.
 - Dropped support for trytond versions below 5.0.
 - Dropped support for Falcon versions below 3.0.

sentry_sdk/tracing.py

@@ -239,14 +239,9 @@ def __init__(
         only_if_parent=False,  # type: bool
         parent_span=None,  # type: Optional[Span]
         otel_span=None,  # type: Optional[OtelSpan]
-        **_,  # type: dict[str, object]
     ):
         # type: (...) -> None
         """
-        For backwards compatibility with old the old Span interface, this class
-        accepts arbitrary keyword arguments, in addition to the ones explicitly
-        listed in the signature. These additional arguments are ignored.
-
         If otel_span is passed explicitly, just acts as a proxy.
 
         If only_if_parent is True, just return an INVALID_SPAN
@@ -284,6 +279,8 @@ def __init__(
                     attributes[SentrySpanAttribute.OP] = op
                 if source is not None:
                     attributes[SentrySpanAttribute.SOURCE] = source
+                if description is not None:
+                    attributes[SentrySpanAttribute.DESCRIPTION] = description
                 if sampled is not None:
                     attributes[SentrySpanAttribute.CUSTOM_SAMPLED] = sampled
 
@@ -543,7 +540,7 @@ def timestamp(self):
 
     def start_child(self, **kwargs):
         # type: (**Any) -> Span
-        return Span(sampled=self.sampled, parent_span=self, **kwargs)
+        return Span(parent_span=self, **kwargs)
 
     def iter_headers(self):
         # type: () -> Iterator[Tuple[str, str]]