EricWF marked 6 inline comments as done.
EricWF added inline comments.
================
Comment at: include/clang/Basic/DiagnosticSemaKinds.td:2129
+def warn_class_template_argument_deduction_no_user_defined_guides : Warning<
+ "class template argument deduction for %0 that has no user defined deduction
guides" >,
+ InGroup<ImplicitCTADUsage>, DefaultIgnore;
----------------
lebedev.ri wrote:
> Quuxplusone wrote:
> > `s/user defined/user-defined/`, and perhaps `s/that has/with/` for brevity.
> `class template argument deduction <was used? happened?> for %0 that has no
> user`
> the sentence looks incomplete to me.
How about `using class template argument deduction for %0 that has no
user-defined deduction guides`?
================
Comment at: test/SemaCXX/cxx1z-class-template-argument-deduction.cpp:426
+// expected-warning@+1 {{class template argument deduction for 'NoExplicit'
that has no user defined deduction guides}}
+NoExplicit ne(42);
+
----------------
Quuxplusone wrote:
> I suggest that additional (more realistic) motivating examples can be found
> in STL's CppCon 2018 talk. E.g.
>
> ```
> template<class T, class U>
> struct Pair {
> T first; U second;
> explicit Pair(const T& t, const U& u) : first(t), second(u) {}
> };
> Pair p(42, "hello world"); // constructs a Pair<int, char[12]>
>
> template<class T, class U>
> struct Pair2 {
> T first; U second;
> explicit Pair2(T t, U u) : first(t), second(u) {}
> };
> Pair2 p(42, "hello world"); // constructs a Pair2<int, const char*>
> ```
>
> I would expect (and, with your patch, receive) diagnostics for both of these.
>
> But for something like `Vector("a", "b")` your patch gives no diagnostic:
> https://godbolt.org/z/_9zhav
> And for something like [`std::optional o(x);` in generic
> context](https://quuxplusone.github.io/blog/2018/12/11/dont-inherit-from-std-types/)
> your patch gives no diagnostic.
>
> I do have a patch out for a general-purpose `-Wctad` that would give warnings
> on those latter cases as well: D54565
> I think `-Wimplicit-ctad` is a good start, but it doesn't solve all the cases
> I'd like to see solved.
I'll add the tests you described. And indeed, this solution is incomplete.
Can you expand on you `std::optional` example? I don't understand it.
Repository:
rC Clang
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https://reviews.llvm.org/D56731/new/
https://reviews.llvm.org/D56731
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