In general, it is a good idea to make unittests @safe and @nogc
in Phobos. When reviewing a pull request, we should check that.
There is a pull request [0] which annotates @system. Why would
you do that? Is that somehow a desirable thing? Should a reviewer
check for that?
The spec for @system [1] says:
System functions are functions not marked with @safe or
@trusted and are not nested inside @safe functions. System
functions may be marked with the @system attribute. A function
being system does not mean it actually is unsafe, it just means
that the compiler is unable to verify that it cannot exhibit
undefined behavior.
[0] https://github.com/dlang/phobos/pull/4532
[1] https://dlang.org/spec/function.html#property-functions
