This is useful for totally terrible stuff that we really dislike, but
for some reason we are afraid to just use `mlog.deprecation()` and
unconditionally tell people so.
Apparently this is because it is totally absolutely vital that, when
telling people something is so broken they should never ever ever use it
no matter what, ever... we can't actually tell them that unless they
bump the minimum version of Meson, because that's our standard way of
introducing a **version number** to tell them when we first started
warning about this.
Sigh. We really want to warn people if they are doing totally broken
stuff no matter what version of Meson they support, because it's not
like fixing the thing that never worked is going to suddenly break old
versions of meson.
So. Here's some new functionality that always warns you, but also tells
you when we started warning.
Use a derived type when passing `subproject` around, so that mypy knows
it's actually a SubProject, not a str. This means that passing anything
other than a handle to the interpreter state's subproject attribute
becomes a type violation, specifically when the order of the *four*
different str arguments is typoed.
This is the final refactoring for extracting the bultin object
logic out of Interpreterbase. I decided to do both arrays and
dicts in one go since splitting it would have been a lot more
confusing.
Another commit in my quest to rid InterpreterBase from all higher
level object processing logic.
Additionally, there is a a logic change here, since `str.join` now
uses varargs and can now accept more than one argument (and supports
list flattening).
This commit introduces a new type of `HoldableObject`: The
`SecondLevelHolder`. The primary purpose of this class is
to handle cases where two (or more) `HoldableObject`s are
stored at the same time (with one default object). The
best (and currently only) example here is the `BothLibraries`
class.