I wrote:
> We might want to start resolving this by inventing a syntax for
> setting a list GUC to an empty list. I'm not very sure what that
> should look like, except that it mustn't be SET ... TO ''.
I experimented with the idea of allowing
SET var TO ;
and got a bunch of shift-reduce conflicts from bison, which don't
look easy to avoid. It's probably a bit too surprising anyway.
This works from a grammar standpoint:
SET var TO NULL;
Because NULL is fully reserved, this isn't usurping any cases that
weren't syntax errors before. It might still be too surprising.
Another idea is that we could redefine a single '' as meaning an empty
list if we were to forbid empty strings as members of GUC_LIST_QUOTE
variables. This doesn't look like it'd be a big issue for the current
set of such variables:
local_preload_libraries
search_path
session_preload_libraries
shared_preload_libraries
temp_tablespaces
unix_socket_directories
We might break some applications that're relying on the current
behavior that an empty item would be effectively ignored.
But that seems a bit remote, and anyway they could just switch
to some other nonexistent name.
Actually, looking at the small number of GUCs that are marked
GUC_LIST_INPUT but not GUC_LIST_QUOTE, I wonder if we shouldn't
prohibit empty strings across-the-board for GUC_LIST_INPUT GUCs.
I don't see any where it'd be useful to allow them. Then we
could allow '' to mean empty list for all of them.
regards, tom lane
