Re: [PATCH/RFC] C++ FE: expression ranges (v2)

[Jakub Jelinek <jakub at redhat dot com>]

On Sat, Nov 21, 2015 at 02:16:49AM -0500, Jason Merrill wrote:
> On 11/19/2015 03:46 PM, Jason Merrill wrote:
> >On 11/15/2015 12:01 AM, David Malcolm wrote:
> >>As with the C frontend, there's an issue with tree nodes that
> >>don't have locations: VAR_DECL, INTEGER_CST, etc:
> >>
> >>   int test (int foo)
> >>   {
> >>     return foo * 100;
> >>            ^^^   ^^^
> >>   }
> >>
> >>where we'd like to access the source spelling ranges of the expressions
> >>during parsing, so that we can use them when reporting parser errors.
> >
> >Hmm, I had been thinking to address this in the C++ front end by
> >wrapping uses in another tree: NOP_EXPR for rvalues, VIEW_CONVERT_EXPR
> >for lvalues.
> 
> On the other hand, my direction seems likely to cause more issues,
> especially with code that doesn't yet know how to handle VIEW_CONVERT_EXPR,
> and could create ambiguity with explicit conversions.  So I guess your
> approach seems reasonable.

But your approach would allow better diagnostics even in places where you
don't have the structures with tree, location_t pairs around.  With that
it will be limited solely to the parser and nothing else, so even template
instantiation if it is something that can be only detected when
instantiating would be too late.

I think using a new tree (rather than using NOP_EXPR/VIEW_CONVERT_EXPR)
that would be just some expression with location and teaching the FE and
folder about it might be even better.

	Jakub