From 875e20fb8ed37322b39ce536fbcf369e3672984b Mon Sep 17 00:00:00 2001
From: anthony sottile <asottile@umich.edu>
Date: Sun, 16 Aug 2026 14:48:20 -0400
Subject: [PATCH] prevent reading unrelated configuration due to commonprefix

---
 pycodestyle.py            |  2 +-
 tests/test_pycodestyle.py | 31 +++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/pycodestyle.py b/pycodestyle.py
index 2343f104..7d781706 100755
--- a/pycodestyle.py
+++ b/pycodestyle.py
@@ -2566,7 +2566,7 @@ def read_config(options, args, arglist, parser):
             print('user configuration: %s' % USER_CONFIG)
         config.read(USER_CONFIG)
 
-    parent = tail = args and os.path.abspath(os.path.commonprefix(args))
+    parent = tail = args and os.path.abspath(os.path.commonpath(args))
     while tail:
         if config.read(os.path.join(parent, fn) for fn in PROJECT_CONFIG):
             local_dir = parent
diff --git a/tests/test_pycodestyle.py b/tests/test_pycodestyle.py
index 444d59f0..868081a9 100644
--- a/tests/test_pycodestyle.py
+++ b/tests/test_pycodestyle.py
@@ -6,7 +6,9 @@
 
 from pycodestyle import Checker
 from pycodestyle import expand_indent
+from pycodestyle import get_parser
 from pycodestyle import mute_string
+from pycodestyle import read_config
 
 
 @pytest.mark.parametrize(
@@ -46,3 +48,32 @@ def test_fstring_logical_line():
         assert checker.logical_line == "f'xxxxxxxxx{thing}xxxxxxxxx'"
     else:
         assert checker.logical_line == "f'xxxxxxxxxxxxxxxxxxxxxxxxx'"
+
+
+def test_read_config_prefix(tmp_path):
+    tmp_path.joinpath('setup.cfg').write_text('[pycodestyle]\nexclude = root')
+
+    adir = tmp_path.joinpath('aaa')
+    adir.mkdir()
+    adir.joinpath('setup.cfg').write_text('[pycodestyle]\nexclude = aaa')
+
+    bdir = tmp_path.joinpath('aaabbb')
+    bdir.mkdir()
+    b_t = bdir.joinpath('t.py')
+    b_t.touch()
+    bdir.joinpath('setup.cfg').write_text('[pycodestyle]\nexclude = bbb')
+
+    cdir = tmp_path.joinpath('aaaccc')
+    cdir.mkdir()
+    c_t = cdir.joinpath('t.py')
+    c_t.touch()
+    cdir.joinpath('setup.cfg').write_text('[pycodestyle]\nexclude = ccc')
+
+    arglist = [str(b_t), str(c_t)]
+    parser = get_parser()
+    parser.add_option('--config')
+    opts, args = parser.parse_args(arglist)
+
+    # `aaa/setup.cfg` should not be read -- it is not passed on cmdline
+    opts = read_config(opts, args, arglist, parser)
+    assert opts.exclude == ['root']