Re: xpath processing brain dead

Robert Haas wrote:
> But the change you're proposing seems like
> it could CONCEIVABLY break a working application that counts on
> PostgreSQL's particular flavor of misbehavior, and therefore it seems
> questionable to put that into a stable branch. The fact that the
> application perhaps should not have been written that way to begin
> with is neither here nor there. We don't want people to be afraid of
> upgrading to the latest point release when we fix, say, a backend
> crash or a data corruption bug.
>
>
>

Let me reiterate the changes that I propose, and again challenge you to
provide a working counter-example if you believe it will break anything
not currently broken, even cases involving fragments.

First, I propose that we abandon this mangling, if, and only if, the xml
is in fact a well formed XML document. Since the whole point of the
mangling is to handle situations where the XML is not a well formed
document, that seems fairly straight-forward. If this change were to
upset any user, it must be because they are relying on undisputably
incorrect results.

Second, I propose that, in the remaining cases, where we do mangle the
XML, if the xpath expression does not begin with a '/', instead of
prepending it with '/x/, which can not possibly be correct under any
circumstance, we prepend it with '/x//' which has some possibility of
giving correct results.

IOW, these proposals will expand the number of correct results from the
code, without contributing any new incorrect cases. These changes are
*very* conservative, as is usual when we fix things on stable branches.

cheers

andrew