Allow Soft Overwrite/Override of Super Methods

[gabizou]

I need to provide an explanation for this:

In the case of having classes Foo and Bar extends Foo, I have times where I want to soft override Foo#baz() when I already have MixinFoo and MixinBar.

In code:

public class Foo {
  public void baz() {
    // something
  }
}

public class Bar extends Foo {
  public void fooBar() {
    // something else
  }
}

@Mixin(Foo.class)
public class MixinFoo {
  @Shadow public void baz() {
    // shadowed! Doesn't actually do anything
  }
}

@Mixin(Bar.class)
public class MixinBar extends MixinFoo {
  @Override
  public void baz() {
    // actually do something different?
  }
}

I've come across wanting this functionality, since Generate > Overwrite methods... is available and Generate > Shadow members... is available. In this case, it'd be easier to do something akin to:
Generate > Override target superclass members (name is whatever) where it first generates the shadowed member method as required (for most cases, should just dummy implement with defaults), and then provide the *exact same method from an Overwrite but as a simple @Override in the subclass mixin.

Examples from Sponge include:
MixinEntityLivingBase

https://github.com/SpongePowered/SpongeCommon/blob/06f890888049ff5fa501c84780076a6e0c8346e9/src/main/java/org/spongepowered/common/mixin/core/entity/MixinEntityLivingBase.java#L205-L207
MixinEntityArmorStand

https://github.com/SpongePowered/SpongeCommon/blob/06f890888049ff5fa501c84780076a6e0c8346e9/src/main/java/org/spongepowered/common/mixin/core/entity/item/MixinEntityArmorStand.java#L216

Of course, this is more of a convenience as more and more of the plugin I get to use to do some fancy things with mixins.

[Mumfrey]

public shadows can just be abstract rather than declared with empty body. Empty body shadow method is only needed when the target is private.

[DenWav]

The plugin never actually creates private shadows, instead preferring protected abstract. But I think @gabizou was just making a point that even if you provided a body, it would do nothing.

[gabizou]

public shadows can just be abstract rather than declared with empty body. Empty body shadow method is only needed when the target is private.

Also needs to be declared empty when you need to call super.foo().

[stale]

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