If $HOME is below a reserved path (for example `/usr/home/thompson`
for Unix traditionalists) or otherwise cannot be shared, or is a
symbolic link to somewhere that cannot be shared, then we will end
up running the app with $HOME not existing. This is unexpected, so
we should make more noise about it.
There are two situations here, both of which get a warning: if we have
--filesystem=home or --filesystem=host then we are trying to share the
real $HOME with the application, and if we do not, then we are trying
to create a directory at the location of the real $HOME and replicate
the chain of symlinks (if any) leading from $HOME to that location.
Unlike the previous commit, this is not expected to happen during unit
testing, so we do not use a g_warning() for this.
Diagnoses: https://github.com/flatpak/flatpak/issues/5035
Signed-off-by: Simon McVittie <smcv@collabora.com>
b85d30365e