From c762d5a7a7c87bf035aabfec9642d555c9dec7e7 Mon Sep 17 00:00:00 2001
From: Rowan Stein <rowan.stein@agyn.io>
Date: Thu, 25 Dec 2025 20:44:48 +0000
Subject: [PATCH] Fix: preserve '.[' in long report headlines by returning
 modpath unchanged; add regression test for param id with '..[' (#22)

---
 src/_pytest/python.py                     |  2 +-
 testing/test_headline_modpath_param_id.py | 24 +++++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 testing/test_headline_modpath_param_id.py

diff --git a/src/_pytest/python.py b/src/_pytest/python.py
index b8b365ad34d..5f2af31e20a 100644
--- a/src/_pytest/python.py
+++ b/src/_pytest/python.py
@@ -286,7 +286,7 @@ def getmodpath(self, stopatmodule=True, includemodule=False):
             parts.append(name)
         parts.reverse()
         s = ".".join(parts)
-        return s.replace(".[", "[")
+        return s
 
     def reportinfo(self):
         # XXX caching?
diff --git a/testing/test_headline_modpath_param_id.py b/testing/test_headline_modpath_param_id.py
new file mode 100644
index 00000000000..6f8b30a6bd3
--- /dev/null
+++ b/testing/test_headline_modpath_param_id.py
@@ -0,0 +1,24 @@
+import pytest
+
+
+def test_headline_preserves_dot_bracket_in_param_id(testdir):
+    testdir.makepyfile(
+        **{
+            "test_sample.py": (
+                """
+                import pytest
+
+                @pytest.mark.parametrize("arg", [0], ids=["a..[b]"])
+                def test_boo(arg):
+                    assert False
+                """
+            )
+        }
+    )
+    result = testdir.runpytest("-vv")
+    # Ensure the failure headline contains the exact param id text without mutation
+    result.stdout.fnmatch_lines([
+        "*FAILURES*",
+        "*test_boo[a..[b]]*",
+    ])
+    assert result.ret != 0