Add UnusedMethodTransformer

The transformer does _not_ check for use via reflection. The only cases
in the 550 and OSRS clients where methods are accessed via reflection
are either 1) JRE classes, 2) when the method name is sent from the
server.

PSVM and methods declared in TypedRemapper.EXCLUDED_METHODS are never
removed.

Signed-off-by: Major <major@emulate.rs>

common/src/main/java/dev/openrs2/common/collect/IterableUtils.kt

@@ -0,0 +1,13 @@
+package dev.openrs2.common.collect
+
+inline fun <T> MutableIterable<T>.removeFirst(predicate: (T) -> Boolean): Boolean {
+    val iterator = iterator()
+    for (element in iterator) {
+        if (predicate(element)) {
+            iterator.remove()
+            return true
+        }
+    }
+
+    return false
+}

deob/src/main/java/dev/openrs2/deob/Deobfuscator.kt

@@ -32,6 +32,7 @@ import dev.openrs2.deob.transform.RemapTransformer
 import dev.openrs2.deob.transform.ResetTransformer
 import dev.openrs2.deob.transform.StaticScramblingTransformer
 import dev.openrs2.deob.transform.UnusedArgTransformer
+import dev.openrs2.deob.transform.UnusedMethodTransformer
 import dev.openrs2.deob.transform.VisibilityTransformer
 import java.nio.file.Files
 import java.nio.file.Path
@@ -168,6 +169,7 @@ class Deobfuscator(private val input: Path, private val output: Path) {
             DummyArgTransformer(),
             DummyLocalTransformer(),
             UnusedArgTransformer(),
+            UnusedMethodTransformer(),
             CounterTransformer(),
             ResetTransformer(),
             ClassLiteralTransformer(),

deob/src/main/java/dev/openrs2/deob/transform/UnusedMethodTransformer.kt

@@ -0,0 +1,86 @@
+package dev.openrs2.deob.transform
+
+import com.github.michaelbull.logging.InlineLogger
+import com.google.common.collect.HashMultimap
+import com.google.common.collect.Multimap
+import dev.openrs2.asm.MemberRef
+import dev.openrs2.asm.classpath.ClassPath
+import dev.openrs2.asm.classpath.Library
+import dev.openrs2.asm.transform.Transformer
+import dev.openrs2.common.collect.DisjointSet
+import dev.openrs2.common.collect.removeFirst
+import dev.openrs2.deob.remap.TypedRemapper
+import org.objectweb.asm.Opcodes
+import org.objectweb.asm.tree.ClassNode
+import org.objectweb.asm.tree.MethodInsnNode
+import org.objectweb.asm.tree.MethodNode
+
+class UnusedMethodTransformer : Transformer() {
+    private lateinit var inheritedMethodSets: DisjointSet<MemberRef>
+    private val methodReferences = HashMultimap.create<DisjointSet.Partition<MemberRef>, MemberRef>()
+
+    override fun preTransform(classPath: ClassPath) {
+        inheritedMethodSets = classPath.createInheritedMethodSets()
+        methodReferences.clear()
+    }
+
+    override fun transformCode(classPath: ClassPath, library: Library, clazz: ClassNode, method: MethodNode): Boolean {
+        for (insn in method.instructions) {
+            if (insn is MethodInsnNode) {
+                addReference(methodReferences, inheritedMethodSets, MemberRef(insn), MemberRef(clazz, method))
+            }
+        }
+
+        return false
+    }
+
+    override fun postTransform(classPath: ClassPath) {
+        var methodsRemoved = 0
+
+        for (library in classPath.libraries) {
+            for (clazz in library) {
+                val methods = clazz.methods.iterator()
+
+                for (method in methods) {
+                    if (method.access and Opcodes.ACC_NATIVE != 0 || method.name in TypedRemapper.EXCLUDED_METHODS) {
+                        continue
+                    }
+
+                    val member = MemberRef(clazz, method)
+                    val partition = inheritedMethodSets[member]!!
+
+                    if (partition.any { classPath[it.owner]!!.dependency }) {
+                        continue
+                    }
+
+                    val references = methodReferences[partition]
+                    if (references.isEmpty() || references.size == 1 && references.first() == member) {
+                        methods.remove()
+                        methodsRemoved++
+
+                        for (ref in partition) {
+                            val owner = library[ref.owner]!!
+                            owner.methods.removeFirst { it.name == ref.name && it.desc == ref.desc }
+                        }
+                    }
+                }
+            }
+        }
+
+        logger.info { "Removed $methodsRemoved unused methods" }
+    }
+
+    private companion object {
+        private val logger = InlineLogger()
+
+        private fun addReference(
+            references: Multimap<DisjointSet.Partition<MemberRef>, MemberRef>,
+            disjointSet: DisjointSet<MemberRef>,
+            member: MemberRef,
+            className: MemberRef
+        ) {
+            val partition = disjointSet[member] ?: return
+            references.put(partition, className)
+        }
+    }
+}