subprojects: Add a README explaining how to manage subprojects

Signed-off-by: Simon McVittie <smcv@collabora.com>

meson.build

@@ -33,7 +33,9 @@ if '@0@.@1@.@2@@3@'.format(
 endif
 
 required_glib = '2.46'
+# Before increasing this, update subprojects/bubblewrap.wrap
 required_bwrap = '0.8.0'
+# Before increasing this, update subprojects/dbus-proxy.wrap
 required_dbus_proxy = '0.1.0'
 required_libostree = '2020.8'
 

subprojects/README.md

@@ -0,0 +1,60 @@
+Subprojects built as part of Flatpak
+====================================
+
+<!-- This document:
+Copyright 2023-2024 Collabora Ltd.
+SPDX-License-Identifier: MIT
+-->
+
+bubblewrap
+----------
+
+Upstream: <https://github.com/containers/bubblewrap>
+
+To use a system copy instead, configure with `-Dsystem_bubblewrap=bwrap`
+or similar.
+
+To update the suggested version, edit bubblewrap.wrap.
+
+dbus-proxy
+----------
+
+Upstream: <https://github.com/flatpak/xdg-dbus-proxy>
+
+To use a system copy instead, configure with
+`-Dsystem_dbus_proxy=xdg-dbus-proxy` or similar.
+
+To update the suggested version, edit dbus-proxy.wrap.
+
+libglnx
+-------
+
+Upstream: <https://gitlab.gnome.org/GNOME/libglnx/>
+
+This is a "copylib", similar to gnulib, which only supports being
+integrated as a subproject and does not guarantee a stable API.
+A suitable version is vendored into Flatpak using `git subtree`, to make
+our source releases self-contained (if system copies of bubblewrap and
+dbus-proxy are used).
+
+To compare with upstream:
+
+    git remote add --no-tags libglnx https://gitlab.gnome.org/GNOME/libglnx.git
+    git fetch libglnx
+    git diff HEAD:subprojects/libglnx libglnx/master
+
+To merge from upstream:
+
+    git fetch libglnx
+    git subtree merge -P subprojects/libglnx libglnx/master
+    git commit --amend -s
+
+variant-schema-compiler
+-----------------------
+
+Upstream: <https://gitlab.gnome.org/alexl/variant-schema-compiler>
+
+This is a "copylib" like libglnx.
+
+To compare with upstream or merge from upstream, the procedure is similar
+to libglnx (see above).