Holding a `Ref` on a garbage-collected object inherently extends any borrow locks on that object. Since ABC files are references already, taking a `Ref` to them only helps to skip the refcount update. This is less useful than expected: in most situations, using `abc_ref` causes double-borrow panics. The few methods that can use it are going to be fragile in the face of future refactors, so I'm nipping the problem in the bud now.
For good measure, most of the other methods in `value` for retrieving pool primitives now also use `TranslationUnit` instead of `AbcFile`. This is the result of a handful of cascading changes throughout the project, and itself caused a few more.
Interface methods are specifically not allowed to be called: as a result, they don't get a method body. Existing code assumed a 1:1 relationship between methods and bodies, which causes spurious errors.
This is inspired by Dinnerbone's similar PR on the AVM1 side, where the Action half of that VM's `Executable` was reduced from 128 bytes to 16 by shoving it in a `Gc`. This won't be as dramatic but should still save some memory.
In fact, it should save a *lot* of memory in bytecode execution, where thanks to the previous commit's rebase, we now need to clone the current method once *for each instruction executed*. That is terrible, but should stop now.
This also results in a far reduced role for `ReturnValue`, since I also took the liberty of removing most of it's use. Furthermore, I also made it apply equally to native and AVM2 code, which ensures all native implementations of methods don't double-borrow.
In AVM1, `ReturnValue` was actually removed entirely, because it's not needed. I attempted to do the same, but the fact that we're currently embedding `ScriptObjectData` in native objects means that we need it for virtual properties. Otherwise, virtual property implementations will see locked objects, which is bad.
While some code that references pool multinames has zero as a valid index, we cannot validate exactly what the zero index is for a given index. Hence, callers instantiating multinames must check for zero and substitute the correct zero-value interpretation for their given type. If zero is an invalid value, it should ideally throw a different error than what's provided here.
This commit breaks the build: we still need to tell `Avm2` how to turn ABC traits into our own internal `Trait<'gc>`, `Class<'gc>`, and `Method<'gc>` types. We also need something to track which traits have already been instantiated, because `callstatic` would otherwise reinstantiate the trait in a different scope. (In fact, I think it *does* do exactly that right now...)
The intention is to completely replace all usage of `Avm2XYZEntry` with `Class`, `Trait`, and `Method`. This will allow runtime-provided global class traits to coexist with those provided by user code.
Inspired by Dinnerbone's PR doing the exact same thing to AVM1.
On AVM2 we have a bit of a subtle issue: the base implementation of `set_property_local` and `init_property_local` *must* return `ReturnValue`s to avoid double-borrows. Each implementation of `TObject` must resolve them before returning.
David Wendt