Remove unused num_instances() method (#8702)

### What

This has been dead-code in our Python SDK for a very long time. No
longer.

---------

Co-authored-by: Clement Rey <[email protected]>

docs/content/reference/migration/migration-0-22.md

@@ -1,9 +1,9 @@
 ---
-title: Migrating from 0.20 to 0.21
-order: 989
+title: Migrating from 0.21 to 0.22
+order: 988
 ---
 
-### Previously deprecated `DisconnectedSpace` archetype/component got now removed.
+### Previously deprecated `DisconnectedSpace` archetype/component got now removed
 
 The deprecated `DisconnectedSpace` archetype and `DisconnectedSpace` component have been removed.
 To achieve the same effect, you can log any of the following "invalid" transforms:
@@ -16,3 +16,12 @@ Previously, the `DisconnectedSpace` archetype played a double role by governing
 This led to a lot of complexity and often broke or caused confusion (see https://github.com/rerun-io/rerun/issues/6817, https://github.com/rerun-io/rerun/issues/4465, https://github.com/rerun-io/rerun/issues/4221).
 By now, explicit blueprints offer a better way to express which views should be spawned and what content they should query.
 (you can learn more about blueprints [here](https://rerun.io/docs/getting-started/configure-the-viewer/through-code-tutorial)).
+
+
+### Removed `num_instances` keyword argument to `rr.log_components()`
+
+For historical reasons, the `rr.log_components()` function of the Python SDK accepts an optional, keyword-only argument `num_instances`.
+It was no longer used for several releases, so we removed it.
+
+**Note**: although `rr.log_components()` is technically a public API, it is undocumented, and we discourage using it.
+For logging custom components, use [`rr.AnyValue`](https://ref.rerun.io/docs/python/main/common/custom_data/#rerun.AnyValues) and [`rr.AnyBatchValue`](https://ref.rerun.io/docs/python/main/common/custom_data/#rerun.AnyBatchValue).

rerun_py/rerun_sdk/rerun/_baseclasses.py

@@ -147,13 +147,7 @@ def as_arrow_array(self) -> pa.Array:
 
 
 class AsComponents(Protocol):
-    """
-    Describes interface for interpreting an object as a bundle of Components.
-
-    Note: the `num_instances()` function is an optional part of this interface. The method does not need to be
-    implemented as it is only used after checking for its existence. (There is unfortunately no way to express this
-    correctly with the Python typing system, see <https://github.com/python/typing/issues/601>).
-    """
+    """Describes interface for interpreting an object as a bundle of Components."""
 
     def as_component_batches(self) -> Iterable[ComponentBatchLike]:
         """
@@ -198,22 +192,6 @@ def indicator(cls) -> ComponentBatchLike:
 
         return IndicatorComponentBatch(cls.archetype_name())
 
-    def num_instances(self) -> int:
-        """
-        The number of instances that make up the batch.
-
-        Part of the `AsComponents` logging interface.
-        """
-        num_instances = 0
-        for fld in fields(type(self)):
-            if "component" in fld.metadata:
-                try:
-                    num_instances = max(num_instances, len(getattr(self, fld.name)))
-                except TypeError:  # Happens for indicator batches.
-                    num_instances = max(num_instances, 1)
-
-        return num_instances
-
     def as_component_batches(self) -> Iterable[ComponentBatchLike]:
         """
         Return all the component batches that make up the archetype.

rerun_py/rerun_sdk/rerun/_log.py

@@ -172,15 +172,9 @@ def log(
                 f"but got {type(entity)} instead."
             )
 
-    if hasattr(entity, "num_instances"):
-        num_instances = entity.num_instances()
-    else:
-        num_instances = None
-
     log_components(
         entity_path=entity_path,
         components=components,
-        num_instances=num_instances,
         static=static,
         recording=recording,  # NOLINT
     )
@@ -191,7 +185,6 @@ def log_components(
     entity_path: str | list[str],
     components: Iterable[ComponentBatchLike],
     *,
-    num_instances: int | None = None,
     timeless: bool = False,
     static: bool = False,
     recording: RecordingStream | None = None,
@@ -216,11 +209,7 @@ def log_components(
         See <https://www.rerun.io/docs/concepts/entity-path> for more on entity paths.
 
     components:
-        A collection of `ComponentBatchLike` objects that
-
-    num_instances:
-        Optional. The number of instances in each batch. If not provided, the max of all
-        components will be used instead.
+        A collection of `ComponentBatchLike` objects.
 
     timeless:
         Deprecated. Refer to `static` instead.
@@ -263,9 +252,6 @@ def log_components(
     descriptors = [comp.component_descriptor() for comp in components]
     arrow_arrays = [comp.as_arrow_array() for comp in components]
 
-    if num_instances is None:
-        num_instances = max(len(arr) for arr in arrow_arrays)
-
     if isinstance(entity_path, list):
         entity_path = bindings.new_entity_path([str(part) for part in entity_path])
 

rerun_py/rerun_sdk/rerun/components/view_coordinates_ext.py

@@ -36,10 +36,6 @@ def as_component_batches(self) -> Iterable[ComponentBatchLike]:
 
         return ViewCoordinates(cast(ViewCoordinatesComponent, self)).as_component_batches()
 
-    def num_instances(self) -> int:
-        # Always a mono-component
-        return 1
-
     # <BEGIN_GENERATED:declarations>
     # This section is generated by running `scripts/generate_view_coordinate_defs.py --python`
     # The following declarations are replaced in `deferred_patch_class`.