Return single element from coroutine callback (#4609)

scrapy/utils/spider.py

@@ -1,5 +1,5 @@
-import logging
 import inspect
+import logging
 
 from scrapy.spiders import Spider
 from scrapy.utils.defer import deferred_from_coro
@@ -18,7 +18,11 @@ def iterate_spider_output(result):
         d = deferred_from_coro(collect_asyncgen(result))
         d.addCallback(iterate_spider_output)
         return d
-    return arg_to_iter(deferred_from_coro(result))
+    elif inspect.iscoroutine(result):
+        d = deferred_from_coro(result)
+        d.addCallback(iterate_spider_output)
+        return d
+    return arg_to_iter(result)
 
 
 def iter_spider_classes(module):

tests/spiders.py

@@ -119,6 +119,17 @@ class AsyncDefAsyncioReturnSpider(SimpleSpider):
         return [{'id': 1}, {'id': 2}]
 
 
+class AsyncDefAsyncioReturnSingleElementSpider(SimpleSpider):
+
+    name = "asyncdef_asyncio_return_single_element"
+
+    async def parse(self, response):
+        await asyncio.sleep(0.1)
+        status = await get_from_asyncio_queue(response.status)
+        self.logger.info("Got response %d" % status)
+        return {"foo": 42}
+
+
 class AsyncDefAsyncioReqsReturnSpider(SimpleSpider):
 
     name = 'asyncdef_asyncio_reqs_return'

tests/test_crawl.py

@@ -21,6 +21,7 @@ from scrapy.utils.python import to_unicode
 from tests.mockserver import MockServer
 from tests.spiders import (
     AsyncDefAsyncioReqsReturnSpider,
+    AsyncDefAsyncioReturnSingleElementSpider,
     AsyncDefAsyncioReturnSpider,
     AsyncDefAsyncioSpider,
     AsyncDefSpider,
@@ -364,6 +365,21 @@ with multiples lines
         self.assertIn({'id': 1}, items)
         self.assertIn({'id': 2}, items)
 
+    @mark.only_asyncio()
+    @defer.inlineCallbacks
+    def test_async_def_asyncio_parse_items_single_element(self):
+        items = []
+
+        def _on_item_scraped(item):
+            items.append(item)
+
+        crawler = self.runner.create_crawler(AsyncDefAsyncioReturnSingleElementSpider)
+        crawler.signals.connect(_on_item_scraped, signals.item_scraped)
+        with LogCapture() as log:
+            yield crawler.crawl(self.mockserver.url("/status?n=200"), mockserver=self.mockserver)
+        self.assertIn("Got response 200", str(log))
+        self.assertIn({"foo": 42}, items)
+
     @mark.skipif(sys.version_info < (3, 6), reason="Async generators require Python 3.6 or higher")
     @mark.only_asyncio()
     @defer.inlineCallbacks