Add an API for querying inheritance

[coderbot16]

[2:38 PM] coderbot: patchwork needs inheritance information for figuring out when a class extends a given Minecraft class (I want to have a system for automatically detecting forge features used by a mod), and/or figuring out the list of classes that a giuven class extends (for propagating event bus handlers)
[2:39 PM] coderbot: it also needs to know if a mod extends a vanilla class for the purposes for evaluating how a mod uses their ATs for the purposes of remaking them into mixins
[2:39 PM] coderbot: if tiny-remapper had a general purpose API for querying inheritance, that would be great

As Player suggested on Discord, it seems like ClassInstance#children fufills this requirement, but there would need to be a public interface for accessing it.

[liach]

@sfPlayer1 Does this

tiny-remapper/src/main/java/net/fabricmc/tinyremapper/api/TrClass.java

Line 19 in 4d0c5a8

TrClass getSuperClass();

api fulfill the needs? If yes, we can close this issue.

[LogicFan]

You can only get parents through the current API, not the childern. But I think it's possible to add an API for this. This will up to @sfPlayer1 .

[liach]

Querying children is always unreliable, as even the JVM doesn't know the full set of children for any non-final (or non-sealed) class at runtime; new classes can always be loaded to extend an existing class.

[LogicFan]

Querying children is always unreliable, as even the JVM doesn't know the full set of children for any non-final (or non-sealed) class at runtime; new classes can always be loaded to extend an existing class.

What you said is true in general. However, for tiny-remapper, if you give all class files into tiny-remapper, then it does know all the children (ofc limited in what your input is). And there is a field ClassInstance#children that contains this information after the propagation stage.

Just need to add

Collection<TrClass> getChildren() {
  return Collections.unmodifiedList(this.childern);
}

should do the trick. However, some consideration is needed.

1. Should we return TrClass or String?
2. Should we also have getParents?
3. Is this good as an API design?

[liach]

for the purpose seen in the original issue, I think getting the parent is enough.

In addition, we have

tiny-remapper/src/main/java/net/fabricmc/tinyremapper/api/TrClass.java

Line 20 in 4d0c5a8

List<? extends TrClass> getInterfaces();

So I argue that our current api suffices for the use cases.