On Mon, Mar 13, 2017 at 5:21 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
"Daniel Verite" <daniel@manitou-mail.org> writes: > Tom Lane wrote: >> when we see \if is that we do nothing but absorb text >> until we see the matching \endif. At that point we could bitch and throw >> everything away if, say, there's \elif after \else, or anything else you >> want to regard as a "compile time error". Otherwise we start execution, >> and from there on it probably has to behave as we've been discussing. >> But this'd be pretty unfriendly from an interactive standpoint, and I'm >> not really convinced that it makes for significantly better error >> reporting.
> On the whole, isn't that a reasonable model to follow for psql?
One thing that occurs to me after more thought is that with such a model, we could not have different lexing rules for live vs not-live branches, since we would not have made those decisions before scanning the input. This seems problematic. Even if you discount the question of whether variable expansion is allowed to change command-boundary decisions, we'd still not want backtick execution to happen everywhere in the block, ISTM.
Maybe we could fix things so that backtick execution happens later, but it would be a pretty significant and invasive change to backslash command execution, I'm afraid.
regards, tom lane
Ok, I've got some time now and I'm starting to dig into this. I'd like to restate what I *think* my feedback is, in case I missed or misunderstood something.
1. Convert perl tests to a single regular regression test.
2. Have MainLoop() pass the cond_stack to the lexer via psql_scan_set_passthrough(scan_state, (void *) cond_stack);
3. Change command scans to scan the whole boolean expression, not just OT_NORMAL.
There's a couple ways to go about this. My gut reaction is to create a new scan type OT_BOOL_EXPR, which for the time being is the same as OT_WHOLE_LINE, but could one day be something different.
4. Change variable expansion and backtick execution in false branches to match new policy.
I've inferred that current preference would be for no expansion and no execution.
5. Allow contextually-correct invalid boolean expressions to map to false.
Out-of-context \endif, \else, and \elif commands remain as errors to be ignored, invalid expressions in an \if or legallyl-placed \elif are just treated as false.
