Make the root warning silence flag multi-state (#11035)

Instead of a flag, make the option take an argument like this:

    --root-user-action=ignore

This allows us to add more alternatives in the future, for example to
emit a hard error when a root user is detected.

Also re-label the news fragment to point to the issue instead of the PR
that introduced the option.

src/pip/_internal/cli/cmdoptions.py

@@ -853,13 +853,13 @@ def _handle_no_use_pep517(
     "of pip is available for download. Implied with --no-index.",
 )
 
-warn_about_root_user: Callable[..., Option] = partial(
+root_user_action: Callable[..., Option] = partial(
     Option,
-    "--no-warn-when-using-as-a-root-user",
-    dest="warn_about_root_user",
-    default=True,
-    action="store_false",
-    help="Do not warn when used as a root user",
+    "--root-user-action",
+    dest="root_user_action",
+    default="warn",
+    choices=["warn", "ignore"],
+    help="Action if pip is run as a root user. By default, a warning message is shown.",
 )
 
 

src/pip/_internal/commands/install.py

@@ -227,7 +227,7 @@ def add_options(self) -> None:
         self.cmd_opts.add_option(cmdoptions.prefer_binary())
         self.cmd_opts.add_option(cmdoptions.require_hashes())
         self.cmd_opts.add_option(cmdoptions.progress_bar())
-        self.cmd_opts.add_option(cmdoptions.warn_about_root_user())
+        self.cmd_opts.add_option(cmdoptions.root_user_action())
 
         index_opts = cmdoptions.make_option_group(
             cmdoptions.index_group,
@@ -464,7 +464,7 @@ def run(self, options: Values, args: List[str]) -> int:
             self._handle_target_dir(
                 options.target_dir, target_temp_dir, options.upgrade
             )
-        if options.warn_about_root_user:
+        if options.root_user_action == "warn":
             warn_if_run_as_root()
         return SUCCESS
 

src/pip/_internal/commands/uninstall.py

@@ -54,7 +54,7 @@ def add_options(self) -> None:
             action="store_true",
             help="Don't ask for confirmation of uninstall deletions.",
         )
-        self.cmd_opts.add_option(cmdoptions.warn_about_root_user())
+        self.cmd_opts.add_option(cmdoptions.root_user_action())
         self.parser.insert_option_group(0, self.cmd_opts)
 
     def run(self, options: Values, args: List[str]) -> int:
@@ -101,6 +101,6 @@ def run(self, options: Values, args: List[str]) -> int:
             )
             if uninstall_pathset:
                 uninstall_pathset.commit()
-        if options.warn_about_root_user:
+        if options.root_user_action == "warn":
             warn_if_run_as_root()
         return SUCCESS