Fix issue #13817: Fixed AttributeError in Argument.__repr__ when dest attribute is not set.

AUTHORS

@@ -441,6 +441,7 @@ Sylvain Marié
 Tadek Teleżyński
 Takafumi Arakaki
 Takumi Otani
+Tammy Hartline
 Taneli Hukkinen
 Tanvi Mehta
 Tanya Agarwal

changelog/13817.bugfix.rst

@@ -0,0 +1 @@
+Fixed ``AttributeError`` in ``Argument.__repr__`` when ``dest`` attribute is not set, which occurred when displaying error messages for invalid option names. The error now shows a helpful message instead of masking the original validation error.

src/_pytest/config/argparsing.py

@@ -359,7 +359,7 @@ def __repr__(self) -> str:
             args += ["_short_opts: " + repr(self._short_opts)]
         if self._long_opts:
             args += ["_long_opts: " + repr(self._long_opts)]
-        args += ["dest: " + repr(self.dest)]
+        args += ["dest: " + repr(getattr(self, "dest", NOT_SET))]
         if hasattr(self, "type"):
             args += ["type: " + repr(self.type)]
         if hasattr(self, "default"):

testing/test_argparsing_repr_fix.py

@@ -0,0 +1,79 @@
+"""Test case for issue #13817: AttributeError with invalid flag in pytest_addoption."""
+
+from __future__ import annotations
+
+from _pytest.config.argparsing import ArgumentError
+from _pytest.config.argparsing import Parser
+import pytest
+
+
+# Suppress warning about using private pytest API (we're testing pytest itself)
+@pytest.mark.filterwarnings("ignore::pytest.PytestDeprecationWarning")
+class TestArgumentReprFix:
+    """Test that Argument.__repr__ handles missing dest attribute."""
+
+    def test_invalid_option_without_dashes(self) -> None:
+        """Test that invalid option names produce helpful error messages."""
+        parser = Parser()
+
+        with pytest.raises(ArgumentError) as exc_info:
+            parser.addoption("shuffle")  # Missing required -- prefix
+
+        error_message = str(exc_info.value)
+        assert "invalid long option string" in error_message
+        assert "shuffle" in error_message
+        assert "must start with --" in error_message
+
+        # Ensure no AttributeError is mentioned
+        assert "AttributeError" not in error_message
+        assert "has no attribute 'dest'" not in error_message
+
+    def test_invalid_short_option(self) -> None:
+        """Test that invalid short option names produce helpful error messages."""
+        parser = Parser()
+
+        with pytest.raises(ArgumentError) as exc_info:
+            parser.addoption("-ab")  # 3 chars, treated as invalid long option
+
+        error_message = str(exc_info.value)
+        # -ab is treated as invalid long option (3+ chars)
+        assert (
+            "invalid long option string" in error_message
+            or "invalid short option string" in error_message
+        )
+
+    def test_valid_option_works(self) -> None:
+        """Test that valid options still work correctly."""
+        parser = Parser()
+        parser.addoption("--shuffle", action="store_true", help="Shuffle tests")
+
+        options = parser._anonymous.options
+        assert len(options) > 0
+        assert "--shuffle" in options[0].names()
+
+    def test_repr_with_dest_set(self) -> None:
+        """Test that __repr__ works correctly when dest is set."""
+        parser = Parser()
+        parser.addoption("--valid-option", dest="valid_dest", help="A valid option")
+
+        # Get the argument object and check its repr
+        option = parser._anonymous.options[0]
+        repr_str = repr(option)
+
+        # Should contain the dest
+        assert "dest: 'valid_dest'" in repr_str
+        assert "NOT_SET" not in repr_str
+
+    def test_repr_without_dest(self) -> None:
+        """Test that __repr__ works when dest is not set due to error."""
+        from _pytest.config.argparsing import Argument
+
+        # Create an Argument that will fail during initialization
+        # This triggers the code path where dest is not set
+        try:
+            Argument("invalid")  # No dashes, will fail
+        except ArgumentError as exc:
+            # The repr was called during error creation
+            # Verify it contains NOT_SET representation
+            assert "dest:" in str(exc)
+            assert "NOT_SET" in str(exc) or "<notset>" in str(exc)