Re: Making tab-complete.c easier to maintain

On Wed, Dec 09, 2015 at 08:49:22PM +0900, Michael Paquier wrote:
> On Wed, Dec 9, 2015 at 8:17 PM, Thomas Munro
> <thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> > On Mon, Dec 7, 2015 at 8:41 PM, Michael Paquier
> > <michael(dot)paquier(at)gmail(dot)com> wrote:
> >> On Tue, Nov 17, 2015 at 12:19 AM, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
> >> wrote:
> >>> Thomas Munro wrote:
> >>>> New version attached, merging recent changes.
> >>>
> >>> I wonder about the TailMatches and Matches macros --- wouldn't it be
> >>> better to have a single one, renaming TailMatches to Matches and
> >>> replacing the current Matches() with an initial token that corresponds
> >>> to anchoring to start of command? Just wondering, not terribly attached
> >>> to the idea.
> >>
> >> + /* TODO:TM -- begin temporary, not part of the patch! */
> >> + Assert(!word_matches(NULL, ""));
> >> + [...]
> >> + Assert(!word_matches("foo", ""));
> >> + /* TODO:TM -- end temporary */
> >>
> >> Be sure to not forget to remove that later.
> >
> > Thanks for looking at this Michael. It's probably not much fun to
> > review! Here is a new version with that bit removed. More responses
> > inline below.
>
> I had a hard time not sleeping when reading it... That's very mechanical.
>
> > I agree that would probably be better but Alvaro suggested following
> > the existing logic in the first pass, which was mostly based on tails,
> > and then considering simpler head-based patterns in a future pass.
>
> Fine with me.
>
> So what do we do now? There is your patch, which is already quite big,
> but as well a second patch based on regexps, which is far bigger. And
> at the end they provide a similar result:
>
> Here is for example what the regexp patch does for some complex
> checks, like ALTER TABLE RENAME:
> /* ALTER TABLE xxx RENAME yyy */
> - else if (pg_strcasecmp(prev4_wd, "TABLE") == 0 &&
> - pg_strcasecmp(prev2_wd, "RENAME") == 0 &&
> - pg_strcasecmp(prev_wd, "CONSTRAINT") != 0 &&
> - pg_strcasecmp(prev_wd, "TO") != 0)
> + else if (MATCH("TABLE #id RENAME !CONSTRAINT|TO"))
>
> And what Thomas's patch does:
> + else if (TailMatches5("ALTER", "TABLE", MatchAny, "RENAME", MatchAny) &&
> + !TailMatches1("CONSTRAINT|TO"))
>
> The regexp patch makes the negative checks somewhat easier to read
> (there are 19 positions in tab-complete.c doing that), still inventing
> a new langage and having a heavy refactoring just tab completion of
> psql seems a bit too much IMO, so my heart balances in favor of
> Thomas' stuff. Thoughts from others?

Agreed that the "whole new language" aspect seems like way too big a
hammer, given what it actually does.

Cheers,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
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