Re: PATCH: psql tab completion for SELECT

Edmund Horner <ejrh00(at)gmail(dot)com> writes:
> On 26 January 2018 at 13:44, Vik Fearing <vik(dot)fearing(at)2ndquadrant(dot)com> wrote:
>> On 01/26/2018 01:28 AM, Edmund Horner wrote:
>>> The patch mentioned attempts to put savepoints around the tab
>>> completion query where appropriate.

>> I am -1 on this idea.

> May I ask why? It doesn't stop psql working against older versions,
> as it checks that the server supports savepoints.

I looked into this patch and was disappointed to discover that it had
only a very ad-hoc solution to the problem of version-dependent tab
completion queries. We need something better --- in particular, the
recent prokind changes mean that there needs to be a way to make
SchemaQuery queries version-dependent.

So ... here is a modest proposal. It invents a VersionedQuery concept
and also extends the SchemaQuery infrastructure to allow those to be
versioned. I have not taken this nearly as far as it could be taken,
since it's mostly just proposing mechanism. To illustrate the
VersionedQuery infrastructure, I fixed it so it wouldn't send
publication/subscription queries to pre-v10 servers, and to illustrate
the versioned SchemaQuery infrastructure, I fixed the prokind problems.

If people like this approach, I propose to commit this more or less
as-is. The select-tab-completion patch would then need to be rewritten
to use this infrastructure, but I think that should be straightforward.
As a separate line of work, the infrastructure could be applied to fix
the pre-existing places where tab completion fails against old servers.
But that's probably work for v12 or beyond, unless somebody's really
motivated to do it right now.

regards, tom lane