From 0a137e40b7091b8df4118f1ec6c718a51df6ee4b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adri=C3=A1n=20Chaves?= <adrian@chaves.io>
Date: Sat, 15 Mar 2025 00:55:31 +0100
Subject: [PATCH] Complete test coverage for exception scenarios of
 SpiderMiddleware.process_seeds

---
 scrapy/core/spidermw.py                      | 22 ++++--
 tests/test_spidermiddleware_process_seeds.py | 72 ++++++++++++++++++++
 2 files changed, 87 insertions(+), 7 deletions(-)

diff --git a/scrapy/core/spidermw.py b/scrapy/core/spidermw.py
index c949c3784..f94b8025f 100644
--- a/scrapy/core/spidermw.py
+++ b/scrapy/core/spidermw.py
@@ -372,7 +372,11 @@ class SpiderMiddlewareManager(MiddlewareManager):
     def process_seeds(
         self, spider: Spider
     ) -> Generator[Deferred[Any], Any, AsyncIterator[Any] | None]:
-        self._check_deprecated_start_requests_use(spider)
+        try:
+            self._check_deprecated_start_requests_use(spider)
+        except ValueError as exception:
+            logger.error(exception)
+            return None
         seeds: AsyncIterator[Any]
         if self._use_start_requests:
             sync_seeds = iter(spider.start_requests())
@@ -381,15 +385,19 @@ class SpiderMiddlewareManager(MiddlewareManager):
             )
             seeds = as_async_generator(sync_seeds)
         else:
-            if not isasyncgenfunction(spider.yield_seeds):
+            error_found = False
+            for fn in (spider.yield_seeds, *self.methods["process_seeds"]):
+                if isasyncgenfunction(fn):
+                    continue
                 logger.error(
-                    f"{global_object_name(spider.yield_seeds)} must be an "
-                    f"async generator function, i.e. an async def function "
-                    f"with yield statements."
+                    f"{global_object_name(fn)} must be an async generator "
+                    f"function, i.e. an async def function with yield "
+                    f"statements."
                 )
+                error_found = True
+            if error_found:
                 return None
-            seeds = spider.yield_seeds()
-            seeds = yield self._process_chain("process_seeds", seeds)
+            seeds = yield self._process_chain("process_seeds", spider.yield_seeds())
         return seeds
 
     def _check_deprecated_start_requests_use(self, spider: Spider):
diff --git a/tests/test_spidermiddleware_process_seeds.py b/tests/test_spidermiddleware_process_seeds.py
index f7bac17de..fccdca0f1 100644
--- a/tests/test_spidermiddleware_process_seeds.py
+++ b/tests/test_spidermiddleware_process_seeds.py
@@ -102,6 +102,8 @@ class DeprecatedWrapSpiderMiddleware:
 
 
 class MainTestCase(TestCase):
+    # Helper methods
+
     async def _test(self, spider_middlewares, spider_cls, expected_items):
         actual_items = []
 
@@ -117,6 +119,17 @@ class MainTestCase(TestCase):
         assert crawler.stats.get_value("finish_reason") == "finished"
         assert actual_items == expected_items, f"{actual_items=} != {expected_items=}"
 
+    async def _test_process_seeds(self, _process_seeds, expected_items=None):
+        class TestSpiderMiddleware:
+            process_seeds = _process_seeds
+
+        class TestSpider(Spider):
+            name = "test"
+
+        await self._test([TestSpiderMiddleware], TestSpider, expected_items)
+
+    # Deprecation and universal
+
     async def _test_wrap(self, spider_middleware, spider_cls, expected_items=None):
         expected_items = (
             [ITEM_A, ITEM_B, ITEM_C] if expected_items is None else expected_items
@@ -190,6 +203,8 @@ class MainTestCase(TestCase):
         ):
             await self._test_wrap(DeprecatedWrapSpiderMiddleware, DeprecatedWrapSpider)
 
+    # Sleep tests
+
     async def _test_sleep(self, spider_middlewares):
         class TestSpider(Spider):
             name = "test"
@@ -220,3 +235,60 @@ class MainTestCase(TestCase):
         await self._test_sleep(
             [NoOpSpiderMiddleware, TwistedSleepSpiderMiddleware, NoOpSpiderMiddleware]
         )
+
+    # Bad definitions.
+
+    @deferred_f_from_coro_f
+    async def test_async_function(self):
+        async def process_seeds(mw, seeds):
+            return
+
+        with LogCapture() as log:
+            await self._test_process_seeds(process_seeds, [])
+
+        assert ".process_seeds must be an async generator function" in str(log), log
+
+    @deferred_f_from_coro_f
+    async def test_sync_function(self):
+        def process_seeds(mw, spider):
+            return []
+
+        with LogCapture() as log:
+            await self._test_process_seeds(process_seeds, [])
+
+        assert ".process_seeds must be an async generator function" in str(log)
+
+    @deferred_f_from_coro_f
+    async def test_sync_generator(self):
+        def process_seeds(mw, spider):
+            return
+            yield
+
+        with LogCapture() as log:
+            await self._test_process_seeds(process_seeds, [])
+
+        assert ".process_seeds must be an async generator function" in str(log)
+
+    # Exceptions during iteration.
+
+    @deferred_f_from_coro_f
+    async def test_exception_before_yield(self):
+        async def process_seeds(mw, seeds):
+            raise RuntimeError
+            yield
+
+        with LogCapture() as log:
+            await self._test_process_seeds(process_seeds, [])
+
+        assert "in process_seeds\n    raise RuntimeError" in str(log), log
+
+    @deferred_f_from_coro_f
+    async def test_exception_after_yield(self):
+        async def process_seeds(mw, spider):
+            yield ITEM_A
+            raise RuntimeError
+
+        with LogCapture() as log:
+            await self._test_process_seeds(process_seeds, [ITEM_A])
+
+        assert "in process_seeds\n    raise RuntimeError" in str(log), log