Notify people if /matrix/postgres/data-auto-upgrade-backup exists

roles/matrix-postgres/tasks/setup_postgres.yml

@@ -120,6 +120,25 @@
         - always
   when: "matrix_postgres_enabled|bool and matrix_postgres_additional_databases|length > 0"
 
+- name: Check existence of matrix-postgres backup data path
+  stat:
+    path: "{{ matrix_postgres_data_path }}-auto-upgrade-backup"
+  register: matrix_postgres_data_backup_path_stat
+  when: "matrix_postgres_enabled|bool"
+
+- name: Inject warning if backup data remains
+  set_fact:
+    matrix_playbook_runtime_results: |
+      {{
+        matrix_playbook_runtime_results|default([])
+        +
+        [
+          "NOTE: You have some Postgres backup data in `{{ matrix_postgres_data_path }}-auto-upgrade-backup`, which was created during the last major Postgres update you ran. If your setup works well after this upgrade, feel free to delete this whole directory."
+        ]
+      }}
+  when: "matrix_postgres_enabled|bool and matrix_postgres_data_backup_path_stat.stat.exists"
+
+
 #
 # Tasks related to getting rid of the internal postgres server (if it was previously enabled)
 #
@@ -155,7 +174,6 @@
   when: "not matrix_postgres_enabled|bool"
 
 # We just want to notify the user. Deleting data is too destructive.
-
 - name: Inject warning if matrix-postgres local data remains
   set_fact:
     matrix_playbook_runtime_results: |