[Bug c++/86190] [6/7/8/9 Regression] -Wsign-conversion ignores explicit conversion in some cases

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86190

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Further reduced:


typedef unsigned long size_t;

struct vector {
  typedef size_t size_type;
  size_type size();
};

bool func(vector vec, int var)
{
  return vec.size() < static_cast<size_t>(var);
}


sc.cc: In function 'bool func(vector, int)':
sc.cc:10:23: warning: conversion to 'vector::size_type {aka long unsigned int}'
from 'int' may change the sign of the result [-Wsign-conversion]
   return vec.size() < static_cast<size_t>(var);
                       ^~~~~~~~~~~~~~~~~~~~~~~~