From d2aa91f63ce2fa749e4d8835ea7b771ead29e54a Mon Sep 17 00:00:00 2001
From: Adam Turner <9087854+aa-turner@users.noreply.github.com>
Date: Tue, 25 Apr 2023 11:31:57 +0100
Subject: Revert the default type of ``nitpick_ignore[_regex]`` to ``list``

---
 CHANGES              |  3 +++
 sphinx/config.py     |  4 ++--
 tests/test_config.py | 15 +++++++++++++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/CHANGES b/CHANGES
index f8327b8ea..28cc885b6 100644
--- a/CHANGES
+++ b/CHANGES
@@ -16,6 +16,9 @@ Features added
 Bugs fixed
 ----------
 
+* #11355: Revert the default type of :confval:`nitpick_ignore` and
+  :confval:`nitpick_ignore_regex` to ``list``.
+
 Testing
 --------
 
diff --git a/sphinx/config.py b/sphinx/config.py
index 625746937..ad7c3b568 100644
--- a/sphinx/config.py
+++ b/sphinx/config.py
@@ -132,8 +132,8 @@ class Config:
         'needs_extensions': ({}, None, []),
         'manpages_url': (None, 'env', []),
         'nitpicky': (False, None, []),
-        'nitpick_ignore': (set(), None, [set, list, tuple]),
-        'nitpick_ignore_regex': (set(), None, [set, list, tuple]),
+        'nitpick_ignore': ([], None, [set, list, tuple]),
+        'nitpick_ignore_regex': ([], None, [set, list, tuple]),
         'numfig': (False, 'env', []),
         'numfig_secnum_depth': (1, 'env', []),
         'numfig_format': ({}, 'env', []),  # will be initialized in init_numfig_format()
diff --git a/tests/test_config.py b/tests/test_config.py
index cf42e5c27..ec5d0948f 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -427,3 +427,18 @@ def test_conf_py_no_language(tempdir):
 
     # Then the language is coerced to English
     assert cfg.language == "en"
+
+
+def test_conf_py_nitpick_ignore_list(tempdir):
+    """Regression test for #11355."""
+
+    # Given a conf.py file with no language attribute
+    (tempdir / 'conf.py').write_text("", encoding='utf-8')
+
+    # When we load conf.py into a Config object
+    cfg = Config.read(tempdir, {}, None)
+    cfg.init_values()
+
+    # Then the default nitpick_ignore[_regex] is an empty list
+    assert cfg.nitpick_ignore == []
+    assert cfg.nitpick_ignore_regex == []
-- 
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