Remove repeating contexts in CompositeBindingContext creation

compiler/frontend/src/org/jetbrains/kotlin/resolve/CompositeBindingContext.kt

@@ -25,9 +25,10 @@ import com.intellij.openapi.util.ModificationTracker
 import org.jetbrains.kotlin.psi.KtExpression
 import org.jetbrains.kotlin.resolve.diagnostics.Diagnostics
 import org.jetbrains.kotlin.types.KotlinType
+import java.util.*
 
 class CompositeBindingContext private constructor(
-        private val delegates: List<BindingContext>
+        private val delegates: LinkedHashSet<BindingContext>
 ) : BindingContext {
     override fun getType(expression: KtExpression): KotlinType? {
         return delegates.asSequence().map { it.getType(expression) }.firstOrNull { it != null }
@@ -36,8 +37,9 @@ class CompositeBindingContext private constructor(
     companion object {
         fun create(delegates: List<BindingContext>): BindingContext {
             if (delegates.isEmpty()) return BindingContext.EMPTY
-            if (delegates.size == 1) return delegates.first()
-            return CompositeBindingContext(delegates)
+            val delegatesSet = LinkedHashSet(delegates)
+            if (delegatesSet.size == 1) return delegates.first()
+            return CompositeBindingContext(delegatesSet)
         }
     }
 
@@ -51,7 +53,7 @@ class CompositeBindingContext private constructor(
 
     override fun <K, V> getSliceContents(slice: ReadOnlySlice<K, V>): ImmutableMap<K, V> {
         //we need intermediate map cause ImmutableMap doesn't support same entries obtained from different slices
-        var map = hashMapOf<K, V>()
+        val map = hashMapOf<K, V>()
         delegates.forEach { map.putAll(it.getSliceContents(slice)) }
         return ImmutableMap.builder<K, V>().putAll(map).build()
     }
@@ -72,8 +74,8 @@ class CompositeBindingContext private constructor(
             return delegates.fold(emptySequence<Diagnostic>(), { r, t -> r + t.asSequence() }).iterator()
         }
 
-        override val modificationTracker = object : ModificationTracker {
-            override fun getModificationCount() = delegates.fold(0L, { r, t -> r + t.modificationTracker.modificationCount })
+        override val modificationTracker = ModificationTracker {
+            delegates.fold(0L, { r, t -> r + t.modificationTracker.modificationCount })
         }
 
         override fun all(): Collection<Diagnostic> {