Support defining Spider.start() as a sync generator

scrapy/core/spidermw.py

@@ -8,7 +8,12 @@ from __future__ import annotations
 
 import logging
 from collections.abc import AsyncIterable, Callable, Iterable
-from inspect import isasyncgenfunction, iscoroutine, iscoroutinefunction
+from functools import wraps
+from inspect import (
+    isasyncgenfunction,
+    iscoroutine,
+    isgeneratorfunction,
+)
 from itertools import islice
 from typing import TYPE_CHECKING, Any, TypeVar, Union, cast
 from warnings import warn
@@ -49,6 +54,21 @@ def _isiterable(o: Any) -> bool:
     return isinstance(o, (Iterable, AsyncIterable))
 
 
+def _sync_generator_to_async(f: Callable) -> Callable:
+    @wraps(f)
+    async def wrapper(*args, **kwargs):
+        for item in f(*args, **kwargs):
+            yield item
+
+    return wrapper
+
+
+def _maybe_sync_generator_to_async(f: Callable) -> Callable:
+    if isgeneratorfunction(f):
+        return _sync_generator_to_async(f)
+    return f
+
+
 class SpiderMiddlewareManager(MiddlewareManager):
     component_name = "spider middleware"
 
@@ -380,7 +400,7 @@ class SpiderMiddlewareManager(MiddlewareManager):
             )
             seeds = as_async_generator(sync_seeds)
         else:
-            seeds = yield self._iter_seeds(spider)
+            seeds = yield _maybe_sync_generator_to_async(spider.start)()
             seeds = yield self._process_chain("process_start", seeds)
         return seeds
 
@@ -454,14 +474,6 @@ class SpiderMiddlewareManager(MiddlewareManager):
                 f"https://docs.scrapy.org/en/VERSION/news.html"
             )
 
-    @staticmethod
-    def _iter_seeds(spider: Spider):
-        fn = spider.start
-        if isasyncgenfunction(fn):
-            return fn().__aiter__()
-        assert iscoroutinefunction(fn)
-        return deferred_from_coro(fn())
-
     # This method is only needed until _async compatibility methods are removed.
     @staticmethod
     def _get_async_method_pair(

tests/test_spider_start.py

@@ -75,6 +75,16 @@ class MainTestCase(TestCase):
 
         await self._test_spider(TestSpider, [ITEM_A])
 
+    @deferred_f_from_coro_f
+    async def test_start_sync(self):
+        class TestSpider(Spider):
+            name = "test"
+
+            def start(self):
+                yield ITEM_A
+
+        await self._test_spider(TestSpider, [ITEM_A])
+
     @deferred_f_from_coro_f
     async def test_deprecated(self):
         class TestSpider(Spider):