emerge: add --update-if-installed

This adds a new emerge option '--update-if-installed'.

The use case for such an option is as follows:
- User finds out libfoo-1.2 is buggy.
- They want to upgrade all their systems if libfoo is installed.
- They don't want to install libfoo if it's not already installed.

  Unfortunately, --update fails this last point, hence
  the need for a new option.

Closes: https://github.com/gentoo/portage/pull/988
Signed-off-by: Sam James <sam@gentoo.org>

1 files changed, 16 insertions, 1 deletions

diff --git a/lib/_emerge/depgraph.py b/lib/_emerge/depgraph.py
index 1631ed1264b..412dc7b6f2e 100644
--- a/lib/_emerge/depgraph.py
+++ b/lib/_emerge/depgraph.py
@@ -1,4 +1,4 @@
-# Copyright 1999-2021 Gentoo Authors
+# Copyright 1999-2023 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 import errno
@@ -5019,6 +5019,21 @@ class depgraph:
                     pkg, existing_node = self._select_package(
                         myroot, atom, onlydeps=onlydeps
                     )
+
+                    # Is the package installed (at any version)?
+                    if pkg and "update_if_installed" in self._dynamic_config.myparams:
+                        package_is_installed = any(
+                            self._iter_match_pkgs(
+                                self._frozen_config.roots[myroot], "installed", atom
+                            )
+                        )
+
+                        # This package isn't eligible for selection in the
+                        # merge list as the user passed --update-if-installed
+                        # and it isn't installed.
+                        if not package_is_installed:
+                            continue
+
                     if not pkg:
                         pprovided_match = False
                         for virt_choice in virtuals.get(atom.cp, []):