lifetimebound on more functions, including container methods

[higher-performance]

A suggestion that I wanted to relay:

In the spirit of #59900 and #60020, how about adding [[clang::lifetimebound]] to other functions as well?
Containers in particular seem to have many methods that could benefit from this attribute, including back(), begin(), data(), emplace_back(), find(), insert(), operator[], etc., since all of their outputs require the container to be alive for validity.
Beyond containers, I think this could be similarly used for functions such as std::unique_ptr::get(), std::variant::get_if(), etc.

[philnik777]

Do you have any specific cases where -Wdangling-gsl doesn't catch the problem already?

[higher-performance]

I haven't tried this for all of them, but for example this seems to be one:

#include <set>
#include <string>

int main()
{
	auto pair = std::set<std::string>().insert("a");
	return pair.first->at(0) == 'a';
}

[higher-performance]

Another place where lifetimebound could be added is for view types like basic_string_view and span, e.g.:

llvm-project/libcxx/include/string

Lines 1079 to 1080 in 7949ee0

	_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
	operator __self_view() const _NOEXCEPT { return __self_view(data(), size()); }

Though some of these may be already handled by -Wdangling-gsl.

[ddkilzer]

Here's an example using std::unique_ptr<>.get() that isn't found by -Wdangling:

    std::string_view sv = *std::make_unique<std::string>("Hello world!");
    std::cout << sv << std::endl;