From 0292d23d7a0ad89432c17b6920a6c9f7a01aa85a Mon Sep 17 00:00:00 2001
From: Adrian Chaves <adrian@zyte.com>
Date: Fri, 19 Jun 2026 17:46:22 +0200
Subject: [PATCH] Improve deprecation messaging around
 SCRAPER_SLOT_MAX_ACTIVE_SIZE

---
 scrapy/core/downloader/__init__.py | 42 ++++++++++++++++++++----------
 tests/test_downloader.py           | 31 +++++++++++++++-------
 2 files changed, 50 insertions(+), 23 deletions(-)

diff --git a/scrapy/core/downloader/__init__.py b/scrapy/core/downloader/__init__.py
index d0239414d..23a563d41 100644
--- a/scrapy/core/downloader/__init__.py
+++ b/scrapy/core/downloader/__init__.py
@@ -142,24 +142,38 @@ class Downloader:
             "SCRAPER_SLOT_MAX_ACTIVE_SIZE"
         )
         assert deprecated_setting_priority is not None
-        if deprecated_setting_priority > 0:
-            warn(
-                (
-                    "The SCRAPER_SLOT_MAX_ACTIVE_SIZE setting is deprecated, "
-                    "use RESPONSE_MAX_ACTIVE_SIZE instead."
-                ),
-                ScrapyDeprecationWarning,
-                stacklevel=2,
-            )
         setting_priority = self.settings.getpriority("RESPONSE_MAX_ACTIVE_SIZE")
         assert setting_priority is not None
-        if setting_priority >= deprecated_setting_priority:
-            self._response_max_active_size = self.settings.getint(
-                "RESPONSE_MAX_ACTIVE_SIZE"
-            )
+        if deprecated_setting_priority > 0:
+            if setting_priority >= deprecated_setting_priority:
+                warn(
+                    (
+                        "The SCRAPER_SLOT_MAX_ACTIVE_SIZE setting is deprecated "
+                        "and is being ignored because RESPONSE_MAX_ACTIVE_SIZE is "
+                        "set with an equal or higher priority. Remove "
+                        "SCRAPER_SLOT_MAX_ACTIVE_SIZE from your settings."
+                    ),
+                    ScrapyDeprecationWarning,
+                    stacklevel=2,
+                )
+                self._response_max_active_size = self.settings.getint(
+                    "RESPONSE_MAX_ACTIVE_SIZE"
+                )
+            else:
+                warn(
+                    (
+                        "The SCRAPER_SLOT_MAX_ACTIVE_SIZE setting is deprecated, "
+                        "use RESPONSE_MAX_ACTIVE_SIZE instead."
+                    ),
+                    ScrapyDeprecationWarning,
+                    stacklevel=2,
+                )
+                self._response_max_active_size = self.settings.getint(
+                    "SCRAPER_SLOT_MAX_ACTIVE_SIZE"
+                )
         else:
             self._response_max_active_size = self.settings.getint(
-                "SCRAPER_SLOT_MAX_ACTIVE_SIZE"
+                "RESPONSE_MAX_ACTIVE_SIZE"
             )
         self._response_max_active_size_warned = False
 
diff --git a/tests/test_downloader.py b/tests/test_downloader.py
index 2808fdc2e..095873715 100644
--- a/tests/test_downloader.py
+++ b/tests/test_downloader.py
@@ -26,23 +26,35 @@ class OfflineSpider(Spider):
         pass
 
 
-def _assert_scraper_slot_deprecation(warning_messages):
+def _assert_scraper_slot_deprecation(warning_messages, *, ignored=False):
     """Assert that a crawl emitted exactly one Scrapy deprecation warning, the
     one about SCRAPER_SLOT_MAX_ACTIVE_SIZE.
 
     Only Scrapy deprecation warnings are counted: a crawl may emit unrelated
     warnings (e.g. a ResourceWarning for a socket garbage-collected while the
-    recorder is active), and those must not make the assertion flaky."""
+    recorder is active), and those must not make the assertion flaky.
+
+    Pass ``ignored=True`` when RESPONSE_MAX_ACTIVE_SIZE is set with an equal or
+    higher priority and therefore SCRAPER_SLOT_MAX_ACTIVE_SIZE is being
+    ignored."""
     deprecations = [
         message
         for message in warning_messages
         if issubclass(message.category, ScrapyDeprecationWarning)
     ]
     assert len(deprecations) == 1
-    assert str(deprecations[0].message) == (
-        "The SCRAPER_SLOT_MAX_ACTIVE_SIZE setting is deprecated, use "
-        "RESPONSE_MAX_ACTIVE_SIZE instead."
-    )
+    if ignored:
+        assert str(deprecations[0].message) == (
+            "The SCRAPER_SLOT_MAX_ACTIVE_SIZE setting is deprecated and is "
+            "being ignored because RESPONSE_MAX_ACTIVE_SIZE is set with an "
+            "equal or higher priority. Remove SCRAPER_SLOT_MAX_ACTIVE_SIZE "
+            "from your settings."
+        )
+    else:
+        assert str(deprecations[0].message) == (
+            "The SCRAPER_SLOT_MAX_ACTIVE_SIZE setting is deprecated, use "
+            "RESPONSE_MAX_ACTIVE_SIZE instead."
+        )
 
 
 class gt:
@@ -110,8 +122,9 @@ class TestResponseMaxActiveSize:
     async def test_both(self):
         """Setting RESPONSE_MAX_ACTIVE_SIZE and SCRAPER_SLOT_MAX_ACTIVE_SIZE to
         different values with the same setting priority triggers a deprecation
-        warning about SCRAPER_SLOT_MAX_ACTIVE_SIZE and makes the value of
-        RESPONSE_MAX_ACTIVE_SIZE the effective response max active size."""
+        warning about SCRAPER_SLOT_MAX_ACTIVE_SIZE being ignored, and makes
+        the value of RESPONSE_MAX_ACTIVE_SIZE the effective response max active
+        size."""
         crawler = get_crawler(
             OfflineSpider,
             settings_dict={
@@ -122,7 +135,7 @@ class TestResponseMaxActiveSize:
         with pytest.warns(ScrapyDeprecationWarning) as warning_messages:
             await maybe_deferred_to_future(crawler.crawl())
         assert crawler.engine.downloader._response_max_active_size == 1
-        _assert_scraper_slot_deprecation(warning_messages)
+        _assert_scraper_slot_deprecation(warning_messages, ignored=True)
 
     @coroutine_test
     async def test_both_deprecated_priority(self):