raises: fix regex escaping warning not considering | as needs escaping

The pipe character is a regex metacharacter (alternation operator) but
is_fully_escaped did not include it, so a match pattern like '^foo|bar$'
would be wrongly identified as a fully-escaped literal. This causes
rawmatch to be set incorrectly, leading to misleading diff output on
match failure.

Also add | to the unescape function's character class for consistency.

Author: bysiber

changelog/13192.bugfix.rst

@@ -0,0 +1 @@
+Fixed `|` (pipe) not being treated as a regex meta-character that needs escaping in :func:`pytest.raises(match=...) <pytest.raises>`.

src/_pytest/raises.py

@@ -363,14 +363,14 @@ def _check_raw_type(
 
 def is_fully_escaped(s: str) -> bool:
     # we know we won't compile with re.VERBOSE, so whitespace doesn't need to be escaped
-    metacharacters = "{}()+.*?^$[]"
+    metacharacters = "{}()+.*?^$[]|"
     return not any(
         c in metacharacters and (i == 0 or s[i - 1] != "\\") for (i, c) in enumerate(s)
     )
 
 
 def unescape(s: str) -> str:
-    return re.sub(r"\\([{}()+-.*?^$\[\]\s\\])", r"\1", s)
+    return re.sub(r"\\([{}()+-.*?^$\[\]\s\\|])", r"\1", s)
 
 
 # These classes conceptually differ from ExceptionInfo in that ExceptionInfo is tied, and

testing/python/raises.py

@@ -430,3 +430,12 @@ def test_raises_match_compiled_regex(self) -> None:
         pattern_with_flags = re.compile(r"INVALID LITERAL", re.IGNORECASE)
         with pytest.raises(ValueError, match=pattern_with_flags):
             int("asdf")
+
+    def test_pipe_is_treated_as_regex_metacharacter(self) -> None:
+        """| (pipe) must be recognized as a regex metacharacter."""
+        from _pytest.raises import is_fully_escaped
+        from _pytest.raises import unescape
+
+        assert not is_fully_escaped("foo|bar")
+        assert is_fully_escaped(r"foo\|bar")
+        assert unescape(r"foo\|bar") == "foo|bar"