r177435 - Objective-C [qoi]: Provide improved parse diagnostics when

[jahanian]

On Mar 19, 2013, at 2:29 PM, Jordan Rose <jordan_rose at apple.com> wrote:

> 
> On Mar 19, 2013, at 14:21 , jahanian <fjahanian at apple.com> wrote:
> 
>> 
>> On Mar 19, 2013, at 1:42 PM, Jordan Rose <jordan_rose at apple.com> wrote:
>> 
>>> 
>>> Would it make sense to not just continue but to pretend instead that the '}' is there? I feel like that will give us better recovery. (You'd eliminate those last two errors: "expected '}'" and "missing '@end'".)
>> 
>> I think by 'pretending' you mean insert a '}' before @end and continue. I thought about this but  I did not want to introduce the bookkeeping
>> overhead for the correct case. Do you have a suggestion how to pretend without adding this overhead?
> 
> Hm, I see what you mean—right now we unilaterally consume a closing brace when we exit the loop. The easiest way to solve this is to extract the parsing loop and the T.consumeClose() into a helper function, with an early return for the @end case...but that's not exactly pretty. I guess I'll let you make the call (or stand by the call you already made).

Problem is not avoiding calling of T.consumeClose() in the incorrect case. Problem is that '@' and 'end" are two tokens and we have consumed
'@' already  (this will cause parse error later).  I see two solutions:
1. When seeing '@', lookahead for 'end' and exit the loop while skipping T.consumeClose() . I think this is what you are suggesting. But it involves unnecessary overhead for the common case.
2. If it is possible,  I can insert a '}' two tokens before current token and reset the lexer to the inserted '}'  for the incorrect case, then problem is solved without introducing any undue overhead for
    the common case.

- Fariborz

> 
> Jordan