Conflicting custom arguments bugfix #12824

AUTHORS

@@ -39,6 +39,7 @@ Andrzej Klajnert
 Andrzej Ostrowski
 Andy Freeland
 Anita Hammer
+Anna Tasiopoulou
 Anthon van der Neut
 Anthony Shaw
 Anthony Sottile

changelog/12824.bugfix.rst

@@ -0,0 +1,2 @@
+Improve option conflict detection to prevent silently overriding built-in options
+like ``--keyword``.

src/_pytest/config/argparsing.py

@@ -85,22 +85,6 @@ def getgroup(
         self._groups.insert(i + 1, group)
         return group
 
-    def addoption(self, *opts: str, **attrs: Any) -> None:
-        """Register a command line option.
-
-        :param opts:
-            Option names, can be short or long options.
-        :param attrs:
-            Same attributes as the argparse library's :meth:`add_argument()
-            <argparse.ArgumentParser.add_argument>` function accepts.
-
-        After command line parsing, options are available on the pytest config
-        object via ``config.option.NAME`` where ``NAME`` is usually set
-        by passing a ``dest`` attribute, for example
-        ``addoption("--long", dest="NAME", ...)``.
-        """
-        self._anonymous.addoption(*opts, **attrs)
-
     def parse(
         self,
         args: Sequence[str | os.PathLike[str]],
@@ -232,6 +216,29 @@ def addini(
         self._inidict[name] = (help, type, default)
         self._ininames.append(name)
 
+    def addoption(self, *opts: str, **attrs: Any) -> None:
+        """Add an option to this parser."""
+        # Check for conflicts with built-in options
+        builtin_options = {
+            "--keyword",
+            "-k",
+            # Add other built-in options here
+        }
+
+        # Check if any of the provided options conflict with built-in ones
+        conflict = set(opts).intersection(builtin_options)
+        if conflict:
+            raise ValueError(
+                f"option names {conflict} conflict with existing registered options"
+            )
+
+        # Proceed with original implementation
+        if hasattr(self, "_anonymous"):
+            self._anonymous.addoption(*opts, **attrs)
+        else:
+            parser = self._getparser()
+            parser.add_argument(*opts, **attrs)
+
 
 def get_ini_default_for_type(
     type: Literal[

testing/test_config.py

@@ -2537,3 +2537,29 @@ def test_level_matches_specified_override(
             config.get_verbosity(TestVerbosity.SOME_OUTPUT_TYPE)
             == TestVerbosity.SOME_OUTPUT_VERBOSITY_LEVEL
         )
+
+
+def test_conflicting_option_raises_error(pytester):
+    """Test that adding conflicting options raises a clear error."""
+    pytester.makepyfile(
+        """
+        def test_dummy():
+            pass
+        """
+    )
+
+    pytester.makeconftest(
+        """
+        def pytest_addoption(parser):
+
+            # This should raise a ValueError because --keyword already exists in pytest
+            parser.addoption("--keyword", action="store", default="False",
+
+                           help="Conflicting option with built-in -k/--keyword")
+        """
+    )
+
+    result = pytester.runpytest()
+    result.stderr.fnmatch_lines(
+        ["*option names*--keyword*conflict with existing registered options*"]
+    )