Re: [pushed] c++: build initializer_list<string> in a loop [PR105838]

[Stephan Bergmann <sbergman@redhat.com>]

On 08/12/2022 19:45, Jason Merrill via Gcc-patches wrote:
> Tested x86_64-pc-linux-gnu, applying to trunk.

Bisecting shows this started to break

> $ cat test.cc
> #include <initializer_list>
> template<typename> struct ConstCharArrayDetector;
> template<int N> struct ConstCharArrayDetector<char const[N]> { using Type = int; };
> struct OUString {
>     template<typename T> OUString(T &, typename ConstCharArrayDetector<T>::Type = 0);
> };
> struct Sequence { Sequence(std::initializer_list<OUString>); };
> Sequence f() { return {""}; }

> $ g++ -fsyntax-only test.cc
> test.cc: In function ‘Sequence f()’:
> test.cc:8:26: error: no matching function for call to ‘OUString::OUString(const char* const)’
>     8 | Sequence f() { return {""}; }
>       |                          ^
> test.cc:5:26: note: candidate: ‘template<class T> OUString::OUString(T&, typename ConstCharArrayDetector<T>::Type)’
>     5 |     template<typename T> OUString(T &, typename ConstCharArrayDetector<T>::Type = 0);
>       |                          ^~~~~~~~
> test.cc:5:26: note:   template argument deduction/substitution failed:
> test.cc: In substitution of ‘template<class T> OUString::OUString(T&, typename ConstCharArrayDetector<T>::Type) [with T = const char* const]’:
> test.cc:8:26:   required from here
> test.cc:5:26: error: invalid use of incomplete type ‘struct ConstCharArrayDetector<const char* const>’
> test.cc:2:27: note: declaration of ‘struct ConstCharArrayDetector<const char* const>’
>     2 | template<typename> struct ConstCharArrayDetector;
>       |                           ^~~~~~~~~~~~~~~~~~~~~~
> test.cc:4:8: note: candidate: ‘constexpr OUString::OUString(const OUString&)’
>     4 | struct OUString {
>       |        ^~~~~~~~
> test.cc:4:8: note:   no known conversion for argument 1 from ‘const char* const’ to ‘const OUString&’
> test.cc:4:8: note: candidate: ‘constexpr OUString::OUString(OUString&&)’
> test.cc:4:8: note:   no known conversion for argument 1 from ‘const char* const’ to ‘OUString&&’
> test.cc:8:26: error: conversion from ‘const char* const’ to non-scalar type ‘const OUString’ requested
>     8 | Sequence f() { return {""}; }
>       |                          ^