[Bug c++/88012] New: Expected -Wnarrowing not given inside template class method

[vz-gcc at zeitlins dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88012

            Bug ID: 88012
           Summary: Expected -Wnarrowing not given inside template class
                    method
           Product: gcc
           Version: 8.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vz-gcc at zeitlins dot org
  Target Milestone: ---
              Host: x86_64-linux-gnu
            Target: x86_64-linux-gnu

Using Debian 8.2.0-9 the following code compiles without any errors or
warnings:

% cat -n narrowing.cpp
     1  using Number = unsigned int;
     2
     3  template <int>
     4  struct S {
     5      S() {
     6          const Number x = {-1}; (void)x;
     7      }
     8  };
     9
    10  int main() {
    11      S<1> s;
    12      // const Number y = {-1}; (void)y;
    13  }
% g++-8 -Wall -c narrowing.cpp
% # i.e. no diagnostic output

Uncommenting the line 12 results in the expected error:

% g++-8 -Wall -c narrowing.cpp
narrowing.cpp: In function ‘int main()’:
narrowing.cpp:12:25: error: narrowing conversion of ‘-1’ from ‘int’ to ‘Number’
{aka ‘unsigned int’} inside { } [-Wnarrowing]
     const Number y = {-1}; (void)y;
                         ^

AFAICS the same error should be given for the same code inside S ctor but
somehow the narrowing conversion is not detected there.

Sorry in advance if I'm missing something, but I couldn't find any reason for
this code to be accepted, so reporting it here because it looks like a bug to
me.

FWIW both clang 7 and MSVS 15.7 do report the expected error (and the former
even does it twice for some reason...).