Re: Redefine default result from PQhost()?

Magnus Hagander <magnus(at)hagander(dot)net> writes:
> On Wed, Nov 25, 2015 at 11:59 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I think we should [ return DEFAULT_PGSOCKET_DIR not NULL ]

> I agree with this change in genera. But I wonder if there's a risk here
> that we break some applications isnt' it? It's clearly a backwards
> incompatible change, so wouldn't it require a bump of libpq version?

I don't see why it would need a libpq version bump, as it's not an ABI
breakage. As for breaking application logic, it's true that any app code
that is explicitly checking for NULL would become dead code, but that
seems pretty harmless. It's already the case that apps should be prepared
to get back an explicit socket directory path spec; that would merely
become a more common case than before.

Also, given the precedent of yesterday's psql fix, we should not discount
the idea that we will be *removing* not adding corner-case bugs in some
applications. Failure to check for NULL is probably even more common in
other apps than in psql.

On the other side of the coin, it's worth noting that there is no
well-defined way for libpq-using apps to discover the value of
DEFAULT_PGSOCKET_DIR. (psql is getting it by #include'ing an internal
header file; there is no way to get it from PQconndefaults.) So whatever
an app might have been doing if it did check for NULL is arguably
inherently buggy, and bypassing such code will be a good thing.

regards, tom lane