D-Bus 1.3.1 (2010) introduced the standard "PropertiesChanged" signal
on "org.freedesktop.DBus.Properties". NetworkManager is old, and predates
this API. From that time, it still had it's own PropertiesChanged signal
that are emitted together with the standard ones. NetworkManager
supports the standard PropertiesChanged signal since it switched to
gdbus library in version 1.2.0 (2016).
These own signals are deprecated for a long time already ([1], 2016), and
are hopefully not used by anybody anymore. libnm-glib was using them and
relied on them, but that library is gone. libnm does not use them and neither
does plasma-nm.
Hopefully no users are left that are affected by this API break.
[1] 6fb917178a
Currently "src/" mostly contains the source code of the daemon.
I say mostly, because that is not true, there are also the device,
settings, wwan, ppp plugins, the initrd generator, the pppd and dhcp
helper, and probably more.
Also we have source code under libnm-core/, libnm/, clients/, and
shared/ directories. That is all confusing.
We should have one "src" directory, that contains subdirectories. Those
subdirectories should contain individual parts (libraries or
applications), that possibly have dependencies on other subdirectories.
There should be a flat hierarchy of directories under src/, which
contains individual modules.
As the name "src/" is already taken, that prevents any sensible
restructuring of the code.
As a first step, move "src/" to "src/core/". This gives space to
reorganize the code better by moving individual components into "src/".
For inspiration, look at systemd's "src/" directory.
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/743
