shafik added inline comments.
================
Comment at: clang/test/CXX/temp/temp.arg/temp.arg.nontype/p1-11.cpp:31
IP<&tl> ip7; // expected-error{{non-type template argument of type 'int *' is
not a constant expression}}
+IP<(int*)1> ip8; // expected-error {{non-type template argument does not refer
to any declaration}}
----------------
rsmith wrote:
> efriedma wrote:
> > erichkeane wrote:
> > > shafik wrote:
> > > > shafik wrote:
> > > > > It looks like in C++17 mode we catch this case:
> > > > > https://godbolt.org/z/s43oE5qWE
> > > > Another case to check for:
> > > >
> > > > ```
> > > > IP<(int*)(1-1)> ip9;
> > > > ```
> > > >
> > > > In C++11 the wording use to allow `integer constant expressions`
> > > The new diagnostic here is unfortunate. That 'does not refer to any
> > > declaration' doesn't really let me know that it is illegal because that
> > > isn't a NPE.
> > >
> > > The 'treat it as a null ptr' here is obviously awful, but I find myself
> > > wondering if we can do better on this diagnostic trivially enough?
> > It's easy enough to use a different message; we just need to detect the
> > particular case we're considering, print an error, and return NPV_Error.
> > But I'm not sure what a better diagnostic looks like. "standard C++ does
> > not allow using '(int*)1' as a non-type template argument"? (The fact that
> > null is allowed isn't really relevant here.)
> > It looks like in C++17 mode we catch this case:
> > https://godbolt.org/z/s43oE5qWE
>
> That's diagnosing the cast, not the template argument value. You can get
> around the cast diagnostic by forcing constant folding with a
> `__builtin_constant_p` conditional
> ([example](https://godbolt.org/z/8f8WWTGeM)). Then we diagnose as
> > <source>:7:4: error: non-type template argument refers to subobject '(int
> > *)1'
> ... which seems like a worse diagnostic than the C++11 one, because it's not
> even true.
> That's diagnosing the cast, not the template argument value. You can get
> around the cast diagnostic by forcing constant folding with a
> `__builtin_constant_p` conditional
> ([example](https://godbolt.org/z/8f8WWTGeM)). Then we diagnose as
> > <source>:7:4: error: non-type template argument refers to subobject '(int
> > *)1'
> ... which seems like a worse diagnostic than the C++11 one, because it's not
> even true.
Great point, I missed that earlier.
My point was that if we are catching this in C++17 mode maybe we can reuse the
machinery to catch this other modes as well and fix the diagnostic quality as
well. Although I realize that may not be easy but worth at least understanding.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D134928/new/
https://reviews.llvm.org/D134928
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