[PATCH WIP] Use Levenshtein distance for various misspellings in C frontend v2

[David Malcolm]

On Thu, 2015-09-17 at 13:31 -0600, Jeff Law wrote:
> On 09/16/2015 02:34 AM, Richard Biener wrote:
> >
> > Btw, this looks quite expensive - I'm sure we want to limit the effort
> > here a bit.
> A limiter is reasonable, though as it's been pointed out this only fires 
> during error processing, so we probably have more leeway to take time 
> and see if we can do better error recovery.
> 
> FWIW, I've used this algorithm in totally unrelated projects and while 
> it seems expensive, it's worked out quite nicely.
> 
> >
> > So while the idea might be an improvement to selected cases it can cause
> > confusion as well.  And if using the suggestion for further parsing it can
> > cause worse followup errors (unless we can limit such "fixup" use to the
> > cases where we can parse the result without errors).  Consider
> >
> > foo()
> > {
> >    foz = 1;
> > }
> >
> > if we suggest 'foo' instead of foz then we'll get a more confusing followup
> > error if we actually use it.
> True.  This kind of problem is probably inherent in this kind of "I'm 
> going assume you meant..." error recovery mechanisms.
> 
> And just to be clear, even in a successful recovery scenario, we still 
> issue an error.  The error recovery is just meant to try and give the 
> user a hint what might have gone wrong and gracefully handle the case 
> where they just made a minor goof.  

(nods)

> Obviously the idea here is to cut 
> down on the number of iterations of edit-compile cycle one has to do :-)

In my mind it's more about saving the user from having to locate the
field they really meant within the corresponding structure declaration
(either by grep, or by some cross-referencing tool).

A lot of the time I find myself wishing that the compiler had issued a
note saying "here's the declaration of the struct in question", which
would make it easy for me to go straight there in Emacs.

I wonder what proportion of our users use a cross-referencing tool or
have an IDE that can find this stuff for them, vs those that rely on
grep, and if that should mean something for our diagnostics (I tend to
just rely on grep).

This is rather tangential to this RFE, of course.

Dave