feat(postgresql): add configurable PostgreSQL version for build and CI

Make the Docker image PostgreSQL version configurable via POSTGRES_TAG
build arg, and run CI tests against both PG 17 and PG 15. Print the
PostgreSQL server version in test output for easier debugging.

Author: andinux

.github/workflows/main.yml

@@ -240,8 +240,12 @@ jobs:
 
   postgres-test:
     runs-on: ubuntu-22.04
-    name: postgresql build + test
+    name: postgresql ${{ matrix.postgres_tag }} build + test
     timeout-minutes: 10
+    strategy:
+      fail-fast: false
+      matrix:
+        postgres_tag: ['17', '15']
 
     steps:
 
@@ -250,7 +254,7 @@ jobs:
           submodules: true
 
       - name: build and start postgresql container
-        run: make postgres-docker-rebuild
+        run: POSTGRES_TAG=${{ matrix.postgres_tag }} make postgres-docker-rebuild
 
       - name: wait for postgresql to be ready
         run: |

docker/postgresql/Dockerfile

@@ -1,10 +1,12 @@
 # PostgreSQL Docker image with CloudSync extension pre-installed
-FROM postgres:17
+ARG POSTGRES_TAG=17
+FROM postgres:${POSTGRES_TAG}
 
-# Install build dependencies
+# Derive the major version from PG_MAJOR (set by the official postgres image)
+# and install the matching server-dev package
 RUN apt-get update && apt-get install -y \
     build-essential \
-    postgresql-server-dev-17 \
+    postgresql-server-dev-${PG_MAJOR} \
     git \
     make \
     && rm -rf /var/lib/apt/lists/*

docker/postgresql/docker-compose.yml

@@ -3,6 +3,8 @@ services:
     build:
       context: ../..
       dockerfile: docker/postgresql/Dockerfile
+      args:
+        POSTGRES_TAG: ${POSTGRES_TAG:-17}
     container_name: cloudsync-postgres
     environment:
       POSTGRES_USER: postgres

test/postgresql/01_unittest.sql

@@ -17,7 +17,8 @@ CREATE EXTENSION IF NOT EXISTS cloudsync;
 
 -- 'Test version visibility'
 SELECT cloudsync_version() AS version \gset
-\echo [PASS] (:testid) Test cloudsync_version: :version
+SELECT current_setting('server_version') AS pg_version \gset
+\echo [PASS] (:testid) Test cloudsync_version: :version (PostgreSQL :pg_version)
 
 -- Test uuid generation
 SELECT cloudsync_uuid() AS uuid1 \gset