refactor: work around sign compare warning (hsutter#551)

Author: JohelEGP

include/cpp2util.h

@@ -398,15 +398,16 @@ auto assert_not_null(auto&& p CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT) -> declty
 //
 auto assert_in_bounds(auto&& x, auto&& arg CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT) -> decltype(auto)
     requires (std::is_integral_v<CPP2_TYPEOF(arg)> &&
-             requires { std::ssize(x); x[arg]; std::begin(x) + 2; })
+             requires { std::size(x); std::ssize(x); x[arg]; std::begin(x) + 2; })
 {
-    Bounds.expects(0 <= arg && arg < std::ssize(x), "out of bounds access attempt detected" CPP2_SOURCE_LOCATION_ARG);
+    Bounds.expects(0 <= arg && arg < [&]() -> auto {
+        if constexpr (std::is_signed_v<CPP2_TYPEOF(arg)>) { return std::ssize(x); }
+        else { return std::size(x); }
+    }(), "out of bounds access attempt detected" CPP2_SOURCE_LOCATION_ARG);
     return CPP2_FORWARD(x) [ CPP2_FORWARD(arg) ];
 }
 
 auto assert_in_bounds(auto&& x, auto&& arg CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT) -> decltype(auto)
-    requires (!(std::is_integral_v<CPP2_TYPEOF(arg)> &&
-             requires { std::ssize(x); x[arg]; std::begin(x) + 2; }))
 {
     return CPP2_FORWARD(x) [ CPP2_FORWARD(arg) ];
 }