hubert.reinterpretcast added inline comments.
================
Comment at: lib/AST/ExprCXX.cpp:1478
+ {
+ // We do not want error diagnostics escaping here.
+ Sema::SFINAETrap Trap(S);
----------------
saar.raz wrote:
> hubert.reinterpretcast wrote:
> > saar.raz wrote:
> > > faisalv wrote:
> > > > Hubert: This needs a TODO: the idea is not to drop SFINAE errors, but
> > > > to avoid instantiation that may trigger errors not in the immediate
> > > > context of instantiation. The substitution needs to happen piecewise.
> > > Could you elaborate/give an example where this handling is inappropriate?
> > Determining satisfaction requires normalization (lazy normalization should
> > be considered).
> > The determination of satisfaction then proceeds by handling the left-hand
> > side of conjunction and disjunction constraints before possibly
> > substituting into the right-hand side; i.e., there is short-circuiting
> > behaviour.
> >
> > Example:
> > ```
> > template <typename T>
> > concept C = true;
> >
> > template <typename T>
> > struct Q { static constexpr T value = nullptr; };
> >
> > template <typename T>
> > requires C<T> || T::value
> > struct A { };
> >
> > template <typename T>
> > requires C<T> || Q<T>::value
> > struct B { };
> >
> > A<int> a; // okay
> > B<int> b; // okay
> > ```
> >
> OK I see your point. You said this should be a TODO - do you think this
> should be delayed to a further patch (namely D41569, where we actually deal
> with diagnostics and stuff)?
> About lazy normalization, I tend to think it is not a good idea - you'll
> probably check satisfaction for every defined constraint expression at some
> point, and do that many more times than you'd define a new one
The status quo of this patch with regards to this topic is not quite something
that I would like to commit onto trunk.
As for normalization: The process is needed for distinct purposes with somewhat
differing output requirements.
The order-dependent form (to check for satisfaction) can be integrated with the
substitution and evaluation: that is, the output of normalization is realized
in control flow, and not "stored".
The order-independent form (to check for subsumption) could be delayed until
overload resolution with a constrained candidate reaches the point where
determining subsumption is necessary.
Repository:
rC Clang
https://reviews.llvm.org/D41217
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