nixos/tests/postgresql: test plv8 hardening on non-JIT variants only

PostgreSQL with JIT support enabled doesn't work with plv8. Hence, we'd
get an evaluation failure for each
`nixosTests.postgresql.postgresql.postgresql_jit_X`.

This should be restructured in the future (less VM tests for custom
extensions, but a single VM test for this case to cover). For now, we
should get this fix out and this is a good-enough approach.

nixos/tests/postgresql/postgresql.nix

@@ -14,7 +14,7 @@ let
       postgresql-clauses = makeEnsureTestFor package;
     };
 
-  test-sql = pkgs.writeText "postgresql-test" ''
+  test-sql = enableJIT: pkgs.writeText "postgresql-test" (''
     CREATE EXTENSION pgcrypto; -- just to check if lib loading works
     CREATE TABLE sth (
       id int
@@ -26,6 +26,7 @@ let
     INSERT INTO sth (id) VALUES (1);
     CREATE TABLE xmltest ( doc xml );
     INSERT INTO xmltest (doc) VALUES ('<test>ok</test>'); -- check if libxml2 enabled
+  '' + lib.optionalString enableJIT ''
     -- check if hardening gets relaxed
     CREATE EXTENSION plv8;
     -- try to trigger the V8 JIT, which requires MemoryDenyWriteExecute
@@ -36,24 +37,30 @@ let
       }
       console.log(xs.reduce((acc, x) => acc + x, 0));
     $$ LANGUAGE plv8;
-  '';
+  '');
 
   makeTestForWithBackupAll =
     package: backupAll:
+    let
+      enableJIT = lib.hasInfix "-jit-" package.name;
+    in
     makeTest {
       name = "postgresql${lib.optionalString backupAll "-backup-all"}-${package.name}";
       meta = with lib.maintainers; {
         maintainers = [ zagy ];
       };
 
       nodes.machine =
-        { ... }:
+        { config, ... }:
         {
           services.postgresql = {
-            inherit package;
+            inherit package enableJIT;
             enable = true;
-            enableJIT = lib.hasInfix "-jit-" package.name;
-            extensions = ps: with ps; [ plv8 ];
+            # plv8 doesn't support postgresql with JIT, so we only run the test
+            # for the non-jit variant.
+            # TODO(@Ma27) split this off into its own VM test and move a few other
+            # extension tests to use postgresqlTestExtension.
+            extensions = lib.mkIf (!enableJIT) (ps: with ps; [ plv8 ]);
           };
 
           services.postgresqlBackup = {
@@ -80,7 +87,7 @@ let
 
           with subtest("Postgresql is available just after unit start"):
               machine.succeed(
-                  "cat ${test-sql} | sudo -u postgres psql"
+                  "cat ${test-sql enableJIT} | sudo -u postgres psql"
               )
 
           with subtest("Postgresql survives restart (bug #1735)"):