[PATCH] make.globals: make FEATURES=-binpkg-multi-instance sticky for existing installs

Add a _compat_upgrade.binpkg_multi_instance script that the ebuild
can call in pkg_preinst in order to maintain a backward-compatible
FEATURES=-binpkg-multi-instance default on existing installs where
enabling binpkg-multi-instance could cause disruption.

Bug: https://bugs.gentoo.org/772785
Signed-off-by: Zac Medico <[email protected]>
---
 .../_compat_upgrade/binpkg_multi_instance.py  | 33 +++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 lib/portage/_compat_upgrade/binpkg_multi_instance.py

diff --git a/lib/portage/_compat_upgrade/binpkg_multi_instance.py b/lib/portage/_compat_upgrade/binpkg_multi_instance.py
new file mode 100644
index 000000000..bfeb72baa
--- /dev/null
+++ b/lib/portage/_compat_upgrade/binpkg_multi_instance.py
@@ -0,0 +1,33 @@
+# Copyright 2021 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+import portage
+from portage import os
+from portage.const import GLOBAL_CONFIG_PATH
+
+COMPAT_FEATURES = 'FEATURES="${FEATURES} -binpkg-multi-instance"'
+
+
+def main():
+	"""
+	If the current installation is still has binpkg-multi-instance
+	disabled, then patch make.globals inside ${ED} to maintain backward
+	compatibility. This is intended to be called from the ebuild as
+	follows:
+
+	pkg_preinst() {
+		python_setup
+		env -u FEATURES
+			PYTHONPATH="${D%/}$(python_get_sitedir)${PYTHONPATH:+:${PYTHONPATH}}" \
+			"${PYTHON}" -m portage._compat_upgrade.binpkg_multi_instance || die
+	}
+	"""
+	if 'binpkg-multi-instance' not in portage.settings.features:
+		portage.output.EOutput().einfo('Setting make.globals default {} for backward compatibility'.format(COMPAT_FEATURES))
+		config_path = os.path.join(os.environ['ED'], GLOBAL_CONFIG_PATH.lstrip(os.sep), 'make.globals')
+		with open(config_path, 'at') as f:
+			f.write("{}\n".format(COMPAT_FEATURES))
+
+
+if __name__ == '__main__':
+	main()
-- 
2.26.2