You'll need the following dependencies:
- gnome-settings-daemon >= 3.27
- libaccountsservice-dev
- libgdk-pixbuf2.0-dev
- libgranite-dev >= 5.5.0
- libgtk-3-dev
- libhandy-1-dev >= 0.90.0
- liblightdm-gobject-1-dev
- libmutter-6-dev
- libx11-dev
- meson
- valac
Run meson to configure the build environment and then ninja to build
meson build --prefix=/usr
cd build
ninja
To install, use ninja install
sudo ninja install
Run LightDM in test mode with Xephyr:
lightdm --test-mode --debug
You can then find the debug log in ~/.cache/lightdm/log