[Bug 1992190] Re: Code builds without -Wall, but not with -Wall

[Julian Andres Klode]

Bug is not reproducible in kinetic with packaged versions of fmt and
boost and g++ 12.

Given library versions are not shipped in 20.04.

** Changed in: gcc-9 (Ubuntu)
       Status: New => Invalid

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Title:
  Code builds without -Wall, but not with -Wall

Status in gcc-9 package in Ubuntu:
  Invalid

Bug description:
  The following code

  ----------------------------------
  #include <boost/safe_numerics/safe_integer.hpp>
  #include <fmt/format.h>
  #include <fmt/ostream.h>

  template<typename Stored,
           Stored Min,
           Stored Max,
           typename P,
           typename E>
  struct fmt::formatter<
      boost::safe_numerics::safe_base<
          Stored, Min, Max, P, E
      >
  > : fmt::ostream_formatter
  {
  };

  void test()
  {
      fmt::print("{}", boost::safe_numerics::safe<int>{ 4 });
  }
  ----------------------------------

  , using fmt 9.1.0 and Boost 1.80, builds in Ubuntu 20.04, with the
  default gcc (9.4.0-1ubuntu1~20.04.1), when using "-std=gnu++17 -Os"
  but not when using "-std=gnu++17 -Os -Wall".

  The problem also exists with g++-10 10.3.0-1ubuntu1~20.04.

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