Make Synapse configuration extensible

roles/matrix-synapse/defaults/main.yml

@@ -295,3 +295,33 @@ matrix_synapse_room_list_publication_rules:
     action: allow
 
 matrix_synapse_default_room_version: "4"
+
+# Default Synapse configuration template which covers the generic use case.
+# You can customize it by controlling the various variables inside it.
+#
+# For a more advanced customization, you can extend the default (see `matrix_synapse_configuration_extension_yaml`)
+# or completely replace this variable with your own template.
+matrix_synapse_configuration_yaml: "{{ lookup('template', 'templates/synapse/homeserver.yaml.j2') }}"
+
+matrix_synapse_configuration_extension_yaml: |
+  # Your custom YAML configuration for Synapse goes here.
+  # This configuration extends the default starting configuration (`matrix_synapse_configuration_yaml`).
+  #
+  # You can override individual variables from the default configuration, or introduce new ones.
+  #
+  # If you need something more special, you can take full control by
+  # completely redefining `matrix_synapse_configuration_yaml`.
+  #
+  # Example configuration extension follows:
+  #
+  # server_notices:
+  #   system_mxid_localpart: notices
+  #   system_mxid_display_name: "Server Notices"
+  #   system_mxid_avatar_url: "mxc://server.com/oumMVlgDnLYFaPVkExemNVVZ"
+  #   room_name: "Server Notices"
+
+matrix_synapse_configuration_extension: "{{ matrix_synapse_configuration_extension_yaml|from_yaml if matrix_synapse_configuration_extension_yaml|from_yaml is mapping else {} }}"
+
+# Holds the final Synapse configuration (a combination of the default and its extension).
+# You most likely don't need to touch this variable. Instead, see `matrix_synapse_configuration_yaml`.
+matrix_synapse_configuration: "{{ matrix_synapse_configuration_yaml|from_yaml|combine(matrix_synapse_configuration_extension, recursive=True) }}"