sdkrystian wrote:
@AaronBallman @cor3ntin @mizvekov So, I've made improvements to our
implementation of `isTemplateArgumentList` that allow us to issue a warning
instead of an error for most of the cases where applying the DR breaks existing
code:
```cpp
template<int I>
struct A { int x; };
template<int I, bool J>
struct B { int x; };
template<int I, typename T, int J>
struct C { int x; };
template<int I>
constexpr inline int V = I;
int y;
template<typename T>
void f(T t)
{
t.A<0>::x; // warning: use 'template' keyword to treat 'A' as
a dependent template name
t.B<1, true>::x; // warning: use 'template' keyword to treat 'B' as
a dependent template name
t.C<2, int, 4>::x; // warning: use 'template' keyword to treat 'C' as
a dependent template name
t.A<V<0>>::x; // warning: use 'template' keyword to treat 'A' as
a dependent template name
t.B<1, V<1>>::x; // warning: use 'template' keyword to treat 'B' as
a dependent template name
t.C<V<2>, int, V<3>>::x; // warning: use 'template' keyword to treat 'C' as
a dependent template name
t.A<(1 > 2)>::x; // warning: use 'template' keyword to treat 'A' as
a dependent template name
t.A<(1 < 3)>::x; // warning: use 'template' keyword to treat 'A' as
a dependent template name
t.A<1 < 4>::x; // error: no member named 'x' in the global
namespace
// error: missing 'template' keyword prior to
dependent template name 'A'
t.A<1 > 4>::x; // error: no member named 'x' in the global
namespace
t.A<0>::y; // ok, parsed as '((t.A) < 0) > ::y'
}
```
This is accomplished by (attempting to) look past the end of the potential
_template-argument-list_, and if the token following the `>` is `::`, we try to
parse it as an _id-expression_/type. If it ends up being invalid, then we
consider it being an intended template name and we issue the warning.
Since we can look past the potential _template-argument-list_ in most cases, we
could probably apply CWG1835 in all language modes with minimal impact on
existing code.
https://github.com/llvm/llvm-project/pull/100425
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