Revisit ownership of static fields of a resource type

[stephan-herrmann]

A static field of any type implementing AutoCloseable and tagged as @Owning currently triggers this warning:

Class with resource fields tagged as '@Owning' should implement AutoCloseable

However, doing as recommend does not help. In fact, once you add the super interface and implement close(), there's no obligation to actually close any resource in this method, since this part correctly understands, that this instance method is not responsible for closing a resource held in a static field.

So, that recommendation to implement AutoCloseable is bogus when only static resource fields are present.

The sibling warning is borderline:

It is recommended to mark resource fields as '@Owning' to ensure proper closing

Does the annotation help on a static field? Which entity will be responsible for closing? Any? The annotation can still help to signal that assigning a fresh resource to this field is OK without closing. Interestingly, assigning a fresh resource to a @NotOwning field (static or instance) does not raise a warning (but should).

[stephan-herrmann]

With #2281 and when resource annotations are enabled, static resource fields will unconditionally report the following:
It is not recommended to hold a resource in a static field

Should someone still want to do so, the following idiom can be used:
static @SuppressWarnings("resource") @Owning AutoCloseable myResource;

The @SuppressWarnings annotation will suppress the above new warning, whereas the @Owning annotation avoids that clients assigning into this field will be blamed for not closing. Use at your own risk!

Generally, with some additional fixes in #2281 more fields may need to be marked as @Owning.