Wondering about errors…

[Nick Sabalausky]

On Mon, 27 May 2013 13:32:46 -0700
Walter Bright <newshound2 at digitalmars.com> wrote:

> On 5/27/2013 4:32 AM, Russel Winder wrote:
> > Using rdmd, it appears that the first error in the code can lead the
> > parsing and template handling of everything following to be wrong. I
> > keep finding that I am getting spurious errors about things nothing
> > to do with the actual error, that simply go away when the real
> > error is fixed. This would imply that most errors reported are
> > generally spurious?
> 
> The usual approach to handling errors in a compiler is to guess at
> what the user actually meant, repair the AST according to that guess,
> then continue on. Unfortunately, the guess is usually wrong and the
> result is cascaded errors, of which only the first is meaningful.
> 
> DMD has been gradually switching over to a more novel approach, one
> that I haven't seen elsewhere. Once an error is discovered, the AST
> is marked as "erroneous". That erroneous state propagates upwards to
> the root of the AST, and that any AST that relies on an erroneous AST
> is itself erroneous, and no further error messages are emitted for it.
> 
> The result should be that only "original sin" errors are reported.
> 
> This has already resulted in a great reduction of spurious error
> messages, but clearly we have more work to do.
> 

Is this what all the "error gagging" stuff is all about, or is there
more to that?