anchor.diff:      psqlSchema = "10.0"; # should be 10, but changing it is invasive
       sha256 = "0zhzj9skag1pgqas2rnd217vj41ilaalqna17j47gyngpvhbqmjr";
       this = self.postgresql_10;
  +    thisAttr = "postgresql_10";
       inherit self;
     };
   
  
positive.code:     psqlSchema = "12";
      sha256 = "15gzg778da23sbfmy7sqg443f9ny480301lm7i3vay4m3ls2a3dx";
      this = self.postgresql_12;
      inherit self;
    };
  
  
negative.code:       , this, self, newScope, buildEnv
  
        # source specification
        , version, sha256, psqlSchema,
  
        # for tests
        nixosTests, thisAttr
      }:
    let
      atLeast = lib.versionAtLeast version;
  