Document the ITEM_PROCESSOR setting (#7983)

docs/topics/settings.rst

@@ -1529,6 +1529,20 @@ Default: ``{}``
 A dict containing the pipelines enabled by default in Scrapy. You should never
 modify this setting in your project, modify :setting:`ITEM_PIPELINES` instead.
 
+.. setting:: ITEM_PROCESSOR
+
+ITEM_PROCESSOR
+--------------
+
+Default: ``"scrapy.pipelines.ItemPipelineManager"``
+
+The :ref:`component <topics-components>` that builds the :ref:`item pipeline
+<topics-item-pipeline>` from :setting:`ITEM_PIPELINES` and runs scraped items
+through it. It must implement :class:`~scrapy.pipelines.ItemProcessorProtocol`.
+
+.. autoclass:: scrapy.pipelines.ItemProcessorProtocol
+    :members:
+
 
 .. setting:: JOBDIR
 

scrapy/pipelines/__init__.py

@@ -8,7 +8,7 @@ from __future__ import annotations
 
 import asyncio
 import warnings
-from typing import TYPE_CHECKING, Any, cast
+from typing import TYPE_CHECKING, Any, Protocol, cast
 
 from twisted.internet.defer import Deferred, DeferredList, FirstError
 
@@ -28,6 +28,23 @@ if TYPE_CHECKING:
     from scrapy.settings import Settings
 
 
+class ItemProcessorProtocol(Protocol):
+    """Protocol for item processor implementations.
+
+    See :setting:`ITEM_PROCESSOR`.
+    """
+
+    async def open_spider_async(self) -> None:
+        """Get the item processor ready to process items."""
+
+    async def process_item_async(self, item: Any) -> Any:
+        """Return the processed *item*, or raise
+        :exc:`~scrapy.exceptions.DropItem` to drop it."""
+
+    async def close_spider_async(self) -> None:
+        """Release any resource that the item processor is using."""
+
+
 class ItemPipelineManager(MiddlewareManager):
     component_name = "item pipeline"