Is it invalid to call CommandEncoder::finish in a prepare callback function

[ACGNnsj]

I‘m a newer to egui, so I tried to follow other's examples. And I found that the function item type of CallbackFn::prepare had been changed. Here's a new parameter of type &mut CommandEncoder and a new return type Vec<wgpu::CommandBuffer>.
I tried to invoke CommandEncoder::finish but failed, because the CommandEncoder in the closure is a mutable reference which can't be moved by CommandEncoder::finish.
I have to steal the ownership from the reference or edit CommandEncoder::finish to make it work.
If it's allowed to call CommandEncoder::finish here, CommandEncoder should be changed to value type I think.

[emilk]

NOTE: @Wumpf rewrote this recently in #3253

[Wumpf]

didn't see this ticket so far, don't think the mechanism has changed there much
@ACGNnsj the command encoder you get in is the one that is later on used to record egui render passes, as such you're not allowed to finish it inside of prepare since it is still used later. However, you can create new command encoders (or pass them in), finish those and return the resulting CommandBuffer. These command buffers will be executed prior to the egui command encoder but in the same wgpu::Queue::submit call which can make things quite a bit more efficient.