Re: BUG #13832: Syntax errors are extremely unfriendly

On Mon, Dec 28, 2015 at 2:03 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Tim Hutt <tdhutt(at)gmail(dot)com> writes:
> > On 24 Dec 2015 16:11, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> As far as raw syntax errors go, we're pretty much limited by what Bison
> >> will do; we're unlikely to implement our own parser from scratch just
> >> to improve this. We do go to considerable lengths for semantic
> errors...
>
> > Ah OK I guess this is an issue with Bison - theoretically it should be
> able
> > to say what it expects when it gets an invalid token right?
>
> You would think. I've experimented with Bison's %error-verbose directive,
> but if anything its results are worse than doing nothing: it seems to
> mention only a rather randomly-chosen subset of the possible
> continuations. (That seems to be related to their decision to put a
> fairly small hard limit on the length of their error messages, but even
> allowing for that, what you get seems pretty random.) It's also
> depressingly concrete; instead of something useful like "expected a table
> name here", you get "expected IDENT or ABORT or ABSOLUTE or (all possible
> unreserved keywords...) here", or at least that's what you would get if
> not for the aforesaid problem.
>
> There's been some recent chat in the PG mailing lists about whether we
> could extract tab-completion logic from the grammar specification, which
> is sort of related to this issue. We've not gotten far with that idea
> unfortunately.
>
> regards, tom lane
>

​I don't know what you've looked at for the auto-complete, but I ran across
this example which uses GNU readline:
http://cc.byexamples.com/2008/06/16/gnu-readline-implement-custom-auto-complete/
​

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