raises: add missing | metacharacter to is_fully_escaped and unescape

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 +430,22 @@ 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_metacharacter_not_treated_as_literal(self) -> None:
+        """Regression test: | (pipe) must be recognized as a regex metacharacter.
+
+        When match='^foo|bar$' is used, is_fully_escaped should recognize this
+        as a real regex (not a fully-escaped literal), so that pytest does not
+        attempt an exact-string diff against it.
+        """
+        from _pytest.raises import is_fully_escaped
+        from _pytest.raises import unescape
+
+        # Pipe is a metacharacter and should not be treated as escaped
+        assert not is_fully_escaped("foo|bar")
+
+        # Escaped pipe should be treated as a literal
+        assert is_fully_escaped(r"foo\|bar")
+
+        # unescape should remove the backslash from an escaped pipe
+        assert unescape(r"foo\|bar") == "foo|bar"