config: move _opt2dest maintenance to Parser

It's a low-level concern so low level should handle it. And one less
thing in the `_processopt` callback which hopefully we can eventually
remove.

Author: bluetech

src/_pytest/config/__init__.py

@@ -1083,7 +1083,6 @@ def __init__(
         self.trace = self.pluginmanager.trace.root.get("config")
         self.hook: pluggy.HookRelay = PathAwareHookProxy(self.pluginmanager.hook)  # type: ignore[assignment]
         self._inicache: dict[str, Any] = {}
-        self._opt2dest: dict[str, str] = {}
         self._cleanup_stack = contextlib.ExitStack()
         self.pluginmanager.register(self, "pytestconfig")
         self._configured = False
@@ -1208,9 +1207,6 @@ def fromdictargs(cls, option_dict: Mapping[str, Any], args: list[str]) -> Config
         return config
 
     def _processopt(self, opt: Argument) -> None:
-        for name in opt.names():
-            self._opt2dest[name] = opt.dest
-
         if not hasattr(self.option, opt.dest):
             setattr(self.option, opt.dest, opt.default)
 
@@ -1842,7 +1838,7 @@ def getoption(self, name: str, default: Any = NOTSET, skip: bool = False):
         :param skip: If ``True``, raise :func:`pytest.skip` if option is undeclared or has a ``None`` value.
             Note that even if ``True``, if a default was specified it will be returned instead of a skip.
         """
-        name = self._opt2dest.get(name, name)
+        name = self._parser._opt2dest.get(name, name)
         try:
             val = getattr(self.option, name)
             if val is None and skip:

src/_pytest/config/argparsing.py

@@ -48,6 +48,8 @@ def __init__(
             anonymous_arggroup, "_anonymous", self, _ispytest=True
         )
         self._groups = [self._anonymous]
+        # Maps option strings -> dest, e.g. "-V" and "--version" to "version".
+        self._opt2dest: dict[str, str] = {}
         file_or_dir_arg = self.optparser.add_argument(FILE_OR_DIR, nargs="*")
         file_or_dir_arg.completer = filescompleter  # type: ignore
 
@@ -368,6 +370,8 @@ def _addoption_inner(
         option = Argument(action)
         self.options.append(option)
         if self.parser:
+            for name in option.names():
+                self.parser._opt2dest[name] = option.dest
             self.parser.processoption(option)