Warning Wtype-limits since gcc 10.2

[mjacobse]

Enabling -Wextra leads to several warnings inside span-lite since gcc 10.2, for example (https://godbolt.org/z/7GrYsM):

<source>:1084:25: warning: comparison of unsigned expression in '>= 0' is always true [-Wtype-limits]
 1084 |         span_EXPECTS( 0 <= idx && idx < size() );
      | 

In many places, an index of size_type is checked to be not negative, which results in this warning if the size_type is an unsigned type (which is the default). If size_type is configured to be signed, the check 0 <= idx is of course reasonable. Not quite sure what the best approach would be. Write a helper template function is_negative that checks the type for signedness first and only then performs the check maybe? Or disable the warning entirely, but maybe it could be useful for other cases?

[martinmoene]

Thanks @mjacobse , will have a look at it when back at a real keyboard next week.

[mjacobse]

Thanks 👍