Re: [PATCH] Use PKG_CHECK_MODULES to detect the libxml2 library

Daniel Gustafsson <daniel(at)yesql(dot)se> writes:
>> On 12 Mar 2020, at 17:39, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I'd originally thought that we might back-patch this, but I'm now of
>> the opinion that we probably should not. If pkg-config is present,
>> this can change the default behavior about where we get libxml from,
>> which seems like something not to do in minor releases. (OTOH, it'd
>> only matter if the default pkg-config choice is different from the
>> default xml2-config choice, so maybe the risk of breakage is small
>> enough to be acceptable?)

> I read this is as a preventative patch to stay ahead of future changes to
> packaging. If these changes do materialize, won't they be equally likely to
> hit installations for backbranch minors as v13?

Yeah, that's the argument *for* back-patching. Question is whether it
outweighs the risk of silently breaking somebody's build by linking
to the wrong libxml2 version.

I could go either way, honestly. The risk doesn't seem large, but
it's not zero.

> We refer to both libxml and libxml2 in these paragraphs. Since upstream is
> consistently referring to it as libxml2, maybe we should take this as
> opportunity to switch to that for the docs?

I think we're kind of stuck with "--with-libxml". Conceivably we
could introduce "--with-libxml2", redefine the old switch as an
obsolete alias, and start saying "libxml2" instead of "libxml".
But I'm not sure that's worth the trouble, and it seems like
material for a different patch anyway.

regards, tom lane