Re: [C++ PATCH] Refactor implicit function template implementation and fix 58534, 58536, 58548, 58549 and 58637.

[Adam Butcher <adam at jessamine dot co dot uk>]

On 2013-11-08 18:50, Jason Merrill wrote:
> On 10/31/2013 05:47 AM, Adam Butcher wrote:
> > +         become_template = true;
> >
> > +         push_deferring_access_checks (dk_deferred);
>
> Why is this call here?  I don't see anything in the rest of the
> function that would trigger an access check, or a matching pop.
This is only in the 'fully implicit function template' case; and the 
matching pop is in finish_fully_implicit_template.  It was in the 
original impl which was trying to do all the things that beginning and 
ending an explicit template parameter list did.  Maybe this is 
unnecessary.  I'll see if anything breaks if I remove it.

> > +      /* Create a distinct parameter pack type from the current 
> > parm and add it
> > +        to the replacement args to tsubst below into the generic 
> > function
> > +        parameter.  */
> > +
> > +      tree t = copy_type (TREE_TYPE (TREE_VALUE (TREE_VEC_ELT 
> > (current, i))));
> > +      TYPE_STUB_DECL (t) = TYPE_NAME (t) = TEMPLATE_TYPE_DECL (t);
>
> Is this changing anything?  I'm not sure if we need to copy the decl
> or if we can just reuse it, but either way we need to set the type of
> TEMPLATE_TYPE_DECL (t) to t.
I think it (or at least one of the assignments) is necessary.  It is 
derived from some similar code in tsubst.  I'll have another look into 
it and add TREE_TYPE (TEMPLATE_TYPE_DECL (t)) = t also.  What problem 
will be caused by not setting the latter; is it a consistency issue?  I 
have not seen any probs in testing so far.

> > +      SET_TYPE_STRUCTURAL_EQUALITY (t);
>
> Why not
>
>       TYPE_CANONICAL (t) = canonical_type_parameter (t);
>
> ?
Only for the sake of not exposing this (currently static) function from 
pt.c (or moving the pack convert function into pt.c).  My original impl 
did extern canonical_type_parameter and use that and I think it worked 
as expected.  Would that be preferred?

Cheers,
Adam