feat: test pg_upgrade compatibility with older extension versions

Add test to verify that all extension versions from PostgreSQL 15 can successfully upgrade to PostgreSQL 17 using pg_upgrade.

The test now validates:

- Each PG 15 extension version can be upgraded to PG 17
- Extension update scripts are properly generated during upgrade
- Version handling works correctly with and without update scripts
- Final extension versions match expected values after upgrade

Author: jfroche

nix/ext/tests/default.nix

@@ -129,17 +129,16 @@ let
         };
       testScript =
         { nodes, ... }:
-        let
-          pg17-configuration = "${nodes.server.system.build.toplevel}/specialisation/postgresql17";
-        in
         ''
           from pathlib import Path
           versions = {
             "15": [${lib.concatStringsSep ", " (map (s: ''"${s}"'') (versions "15"))}],
             "17": [${lib.concatStringsSep ", " (map (s: ''"${s}"'') (versions "17"))}],
           }
           extension_name = "${pname}"
-          pg17_configuration = "${pg17-configuration}"
+          system = "${nodes.server.system.build.toplevel}"
+          pg15_configuration = system
+          pg17_configuration = f"{system}/specialisation/postgresql17"
           ext_has_background_worker = ${
             if (installedExtension "15") ? hasBackgroundWorker then "True" else "False"
           }
@@ -191,6 +190,34 @@ let
 
           with subtest("Check pg_regress with postgresql 17 after installing the last version"):
             test.check_pg_regress(Path("${psql_17}/lib/pgxs/src/test/regress/pg_regress"), "17", pg_regress_test_name)
+
+          with subtest("Test pg_upgrade from postgresql 15 to 17 with older extension version"):
+            # Test that all extension versions from postgresql 15 can be upgraded to postgresql 17 using pg_upgrade
+            for version in versions["15"]:
+              server.systemctl("stop postgresql.service")
+              server.succeed("rm -fr /var/lib/postgresql/update_extensions.sql /var/lib/postgresql/17")
+              server.succeed(
+                f"{pg15_configuration}/bin/switch-to-configuration test >&2"
+              )
+              test.drop_extension()
+              test.install_extension(version)
+              server.succeed(
+                f"{pg17_configuration}/bin/switch-to-configuration test >&2"
+              )
+              has_update_script = server.succeed(
+                "test -f /var/lib/postgresql/update_extensions.sql && echo 'yes' || echo 'no'"
+              ).strip() == "yes"
+              if has_update_script:
+                # Run the extension update script generated during the upgrade
+                test.run_sql_file("/var/lib/postgresql/update_extensions.sql")
+              if has_update_script:
+                # If there was an update script, the last version should be installed
+                test.assert_version_matches(versions["17"][-1])
+              else:
+                # Otherwise, the version should match the version from postgresql 15
+                test.assert_version_matches(version)
+
+              test.check_pg_regress(Path("${psql_17}/lib/pgxs/src/test/regress/pg_regress"), "17", pg_regress_test_name)
         '';
     };
 in