From 49bb5c89a6111d39455482fa415a3fd526b3b497 Mon Sep 17 00:00:00 2001
From: Virendra Patil <70162563+virendrapatil24@users.noreply.github.com>
Date: Wed, 3 Jul 2024 00:28:08 +0530
Subject: [PATCH] Improved handling of invalid regex pattern in pytest.raises
 (#12526)

---
 AUTHORS                    |  1 +
 changelog/12505.bugfix.rst |  1 +
 src/_pytest/python_api.py  |  9 +++++++++
 testing/python/raises.py   | 20 ++++++++++++++++++++
 4 files changed, 31 insertions(+)
 create mode 100644 changelog/12505.bugfix.rst

diff --git a/AUTHORS b/AUTHORS
index 26fa27f9b..7fd388505 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -430,6 +430,7 @@ Victor Rodriguez
 Victor Uriarte
 Vidar T. Fauske
 Vijay Arora
+Virendra Patil
 Virgil Dupras
 Vitaly Lashmanov
 Vivaan Verma
diff --git a/changelog/12505.bugfix.rst b/changelog/12505.bugfix.rst
new file mode 100644
index 000000000..f55a8a17e
--- /dev/null
+++ b/changelog/12505.bugfix.rst
@@ -0,0 +1 @@
+Improve handling of invalid regex patterns in :func:`pytest.raises(match=r'...') <pytest.raises>` by providing a clear error message.
diff --git a/src/_pytest/python_api.py b/src/_pytest/python_api.py
index c1e851391..4174a55b5 100644
--- a/src/_pytest/python_api.py
+++ b/src/_pytest/python_api.py
@@ -7,6 +7,7 @@ from decimal import Decimal
 import math
 from numbers import Complex
 import pprint
+import re
 from types import TracebackType
 from typing import Any
 from typing import Callable
@@ -986,6 +987,14 @@ class RaisesContext(ContextManager[_pytest._code.ExceptionInfo[E]]):
         self.message = message
         self.match_expr = match_expr
         self.excinfo: _pytest._code.ExceptionInfo[E] | None = None
+        if self.match_expr is not None:
+            re_error = None
+            try:
+                re.compile(self.match_expr)
+            except re.error as e:
+                re_error = e
+            if re_error is not None:
+                fail(f"Invalid regex pattern provided to 'match': {re_error}")
 
     def __enter__(self) -> _pytest._code.ExceptionInfo[E]:
         self.excinfo = _pytest._code.ExceptionInfo.for_later()
diff --git a/testing/python/raises.py b/testing/python/raises.py
index 271dd3e5a..2011c8161 100644
--- a/testing/python/raises.py
+++ b/testing/python/raises.py
@@ -132,6 +132,26 @@ class TestRaises:
         result = pytester.runpytest()
         result.stdout.fnmatch_lines(["*2 failed*"])
 
+    def test_raises_with_invalid_regex(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """
+            import pytest
+
+            def test_invalid_regex():
+                with pytest.raises(ValueError, match="invalid regex character ["):
+                    raise ValueError()
+            """
+        )
+        result = pytester.runpytest()
+        result.stdout.fnmatch_lines(
+            [
+                "*Invalid regex pattern provided to 'match': unterminated character set at position 24*",
+            ]
+        )
+        result.stdout.no_fnmatch_line("*Traceback*")
+        result.stdout.no_fnmatch_line("*File*")
+        result.stdout.no_fnmatch_line("*line*")
+
     def test_noclass(self) -> None:
         with pytest.raises(TypeError):
             pytest.raises("wrong", lambda: None)  # type: ignore[call-overload]