diff --git a/compiler/frontend/src/org/jetbrains/kotlin/analyzer/AnalyzerFacade.kt b/compiler/frontend/src/org/jetbrains/kotlin/analyzer/AnalyzerFacade.kt
index 5155ef5c305..38c468329fb 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/analyzer/AnalyzerFacade.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/analyzer/AnalyzerFacade.kt
@@ -31,17 +31,15 @@ import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.psi.JetFile
 import org.jetbrains.kotlin.resolve.lazy.ResolveSession
-import org.jetbrains.kotlin.storage.StorageManager
 import java.util.ArrayList
 import java.util.HashMap
-import kotlin.properties.Delegates
 
-public trait ResolverForModule {
+public interface ResolverForModule {
     public val lazyResolveSession: ResolveSession
     public val packageFragmentProvider: PackageFragmentProvider
 }
 
-public trait ResolverForProject<M : ModuleInfo,out R : ResolverForModule> {
+public interface ResolverForProject<M : ModuleInfo,out R : ResolverForModule> {
     public fun resolverForModule(moduleInfo: M): R = resolverForModuleDescriptor(descriptorForModule(moduleInfo))
     public fun descriptorForModule(moduleInfo: M): ModuleDescriptor
     public fun resolverForModuleDescriptor(descriptor: ModuleDescriptor): R
@@ -61,7 +59,7 @@ public class ResolverForProjectImpl<M : ModuleInfo, R : ResolverForModule>(
 ) : ResolverForProject<M, R> {
     val resolverByModuleDescriptor: MutableMap<ModuleDescriptor, () -> R> = HashMap()
 
-    override val allModules: Collection<M> by Delegates.lazy {
+    override val allModules: Collection<M> by lazy {
         (descriptorByModule.keySet() + delegateResolver.allModules).toSet()
     }
 
@@ -87,9 +85,9 @@ public data class ModuleContent(
         public val moduleContentScope: GlobalSearchScope
 )
 
-public trait PlatformAnalysisParameters
+public interface PlatformAnalysisParameters
 
-public trait ModuleInfo {
+public interface ModuleInfo {
     public val isLibrary: Boolean
         get() = false
     public val name: Name
@@ -98,7 +96,7 @@ public trait ModuleInfo {
     public fun dependencyOnBuiltins(): DependencyOnBuiltins = DependenciesOnBuiltins.LAST
 
     //TODO: (module refactoring) provide dependency on builtins after runtime in IDEA
-    public trait DependencyOnBuiltins {
+    public interface DependencyOnBuiltins {
         public fun adjustDependencies(builtinsModule: ModuleDescriptorImpl, dependencies: MutableList<ModuleDescriptorImpl>)
     }
 
@@ -122,7 +120,7 @@ public trait ModuleInfo {
     }
 }
 
-public trait AnalyzerFacade<A : ResolverForModule, in P : PlatformAnalysisParameters> {
+public interface AnalyzerFacade<A : ResolverForModule, in P : PlatformAnalysisParameters> {
     public fun <M : ModuleInfo> setupResolverForProject(
             projectContext: ProjectContext,
             modules: Collection<M>,
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeVariableDataCollector.kt b/compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeVariableDataCollector.kt
index 4c34b8844b0..ae91aa6abb2 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeVariableDataCollector.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeVariableDataCollector.kt
@@ -97,10 +97,10 @@ public class PseudocodeVariableDataCollector(
 }
 
 //todo may be a type alias
-trait InstructionDataMergeStrategy<D> :
+interface InstructionDataMergeStrategy<D> :
   (Instruction, Collection<MutableMap<VariableDescriptor, D>>) -> Edges<MutableMap<VariableDescriptor, D>>
 
-public trait LexicalScopeVariableInfo {
+public interface LexicalScopeVariableInfo {
     val declaredIn : Map<VariableDescriptor, LexicalScope>
     val scopeVariables : Map<LexicalScope, Collection<VariableDescriptor>>
 }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/cfg/UnreachableCode.kt b/compiler/frontend/src/org/jetbrains/kotlin/cfg/UnreachableCode.kt
index 1f9a32e9f63..5504c179b56 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/cfg/UnreachableCode.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/cfg/UnreachableCode.kt
@@ -28,7 +28,7 @@ import org.jetbrains.kotlin.lexer.JetTokens
 import com.intellij.psi.util.PsiTreeUtil
 import com.intellij.psi.PsiComment
 
-trait UnreachableCode {
+interface UnreachableCode {
     val elements: Set<JetElement>
     fun getUnreachableTextRanges(element: JetElement): List<TextRange>
 }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/PseudoValue.kt b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/PseudoValue.kt
index 14641ab2fb0..908bbfa0cde 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/PseudoValue.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/PseudoValue.kt
@@ -19,12 +19,12 @@ package org.jetbrains.kotlin.cfg.pseudocode
 import org.jetbrains.kotlin.psi.JetElement
 import org.jetbrains.kotlin.cfg.pseudocode.instructions.eval.InstructionWithValue
 
-public trait PseudoValue {
+public interface PseudoValue {
     public val debugName: String
     public val element: JetElement?
     public val createdAt: InstructionWithValue?
 }
 
-public trait PseudoValueFactory {
+public interface PseudoValueFactory {
     public fun newValue(element: JetElement?, instruction: InstructionWithValue?): PseudoValue
 }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/TypePredicate.kt b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/TypePredicate.kt
index 18251ebb145..5448e91650f 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/TypePredicate.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/TypePredicate.kt
@@ -23,7 +23,7 @@ import org.jetbrains.kotlin.types.JetType
 import org.jetbrains.kotlin.types.TypeUtils
 import org.jetbrains.kotlin.types.checker.JetTypeChecker
 
-public trait TypePredicate: (JetType) -> Boolean {
+public interface TypePredicate: (JetType) -> Boolean {
     override fun invoke(typeToCheck: JetType): Boolean
 }
 
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/Instruction.kt b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/Instruction.kt
index 10f7cb0f64d..9e7e9cb20d4 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/Instruction.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/Instruction.kt
@@ -19,7 +19,7 @@ package org.jetbrains.kotlin.cfg.pseudocode.instructions
 import org.jetbrains.kotlin.cfg.pseudocode.Pseudocode
 import org.jetbrains.kotlin.cfg.pseudocode.PseudoValue
 
-public trait Instruction {
+public interface Instruction {
     public var owner: Pseudocode
 
     public val previousInstructions: Collection<Instruction>
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/JetElementInstruction.kt b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/JetElementInstruction.kt
index 30636e451e6..6e0e14d10d3 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/JetElementInstruction.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/JetElementInstruction.kt
@@ -18,6 +18,6 @@ package org.jetbrains.kotlin.cfg.pseudocode.instructions
 
 import org.jetbrains.kotlin.psi.JetElement
 
-public trait JetElementInstruction : Instruction {
+public interface JetElementInstruction : Instruction {
     public val element: JetElement
 }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/LexicalScope.kt b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/LexicalScope.kt
index f0d21296ab7..7acd15769b9 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/LexicalScope.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/LexicalScope.kt
@@ -16,23 +16,22 @@
 
 package org.jetbrains.kotlin.cfg.pseudocode.instructions
 
-import org.jetbrains.kotlin.psi.JetElement
 import org.jetbrains.kotlin.psi.JetDeclaration
-import kotlin.properties.Delegates
+import org.jetbrains.kotlin.psi.JetElement
 
 public class LexicalScope(val parentScope: LexicalScope?, val element: JetElement) {
     //todo remove after KT-4126
     private val d = (parentScope?.depth ?: 0) + 1
     val depth: Int get() = d
 
-    val lexicalScopeForContainingDeclaration: LexicalScope? by Delegates.lazy { computeLexicalScopeForContainingDeclaration() }
+    val lexicalScopeForContainingDeclaration: LexicalScope? by lazy { computeLexicalScopeForContainingDeclaration() }
     private fun computeLexicalScopeForContainingDeclaration(): LexicalScope? {
         var scope: LexicalScope? = this
         while (scope != null) {
-            if (scope?.element is JetDeclaration) {
+            if (scope.element is JetDeclaration) {
                 return scope
             }
-            scope = scope?.parentScope
+            scope = scope.parentScope
         }
         return null
     }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/eval/InstructionWithReceivers.kt b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/eval/InstructionWithReceivers.kt
index a7ce13ec90f..043dfa35481 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/eval/InstructionWithReceivers.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/eval/InstructionWithReceivers.kt
@@ -20,6 +20,6 @@ import org.jetbrains.kotlin.cfg.pseudocode.PseudoValue
 import org.jetbrains.kotlin.cfg.pseudocode.instructions.Instruction
 import org.jetbrains.kotlin.resolve.scopes.receivers.ReceiverValue
 
-public trait InstructionWithReceivers: Instruction {
+public interface InstructionWithReceivers: Instruction {
     public val receiverValues: Map<PseudoValue, ReceiverValue>
 }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/eval/InstructionWithValue.kt b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/eval/InstructionWithValue.kt
index 95203cc0109..6296332ffd7 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/eval/InstructionWithValue.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/eval/InstructionWithValue.kt
@@ -19,6 +19,6 @@ package org.jetbrains.kotlin.cfg.pseudocode.instructions.eval
 import org.jetbrains.kotlin.cfg.pseudocode.instructions.JetElementInstruction
 import org.jetbrains.kotlin.cfg.pseudocode.PseudoValue
 
-public trait InstructionWithValue : JetElementInstruction {
+public interface InstructionWithValue : JetElementInstruction {
     public val outputValue: PseudoValue?
 }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/jumps/JumpInstruction.kt b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/jumps/JumpInstruction.kt
index 5927d71a69a..82c3b34452d 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/jumps/JumpInstruction.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/cfg/pseudocode/instructions/jumps/JumpInstruction.kt
@@ -18,4 +18,4 @@ package org.jetbrains.kotlin.cfg.pseudocode.instructions.jumps
 
 import org.jetbrains.kotlin.cfg.pseudocode.instructions.Instruction
 
-public trait JumpInstruction : Instruction
+public interface JumpInstruction : Instruction
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/config/ContentRoots.kt b/compiler/frontend/src/org/jetbrains/kotlin/config/ContentRoots.kt
index e04e3c6f6b8..cc90a828cb6 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/config/ContentRoots.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/config/ContentRoots.kt
@@ -18,7 +18,7 @@ package org.jetbrains.kotlin.config
 
 import java.io.File
 
-public trait ContentRoot
+public interface ContentRoot
 
 public data class KotlinSourceRoot(public val path: String): ContentRoot
 
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/extensions/ExternalDeclarationsProvider.kt b/compiler/frontend/src/org/jetbrains/kotlin/extensions/ExternalDeclarationsProvider.kt
index 1f219981b3d..86d7f999f36 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/extensions/ExternalDeclarationsProvider.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/extensions/ExternalDeclarationsProvider.kt
@@ -20,7 +20,7 @@ import org.jetbrains.kotlin.extensions.ProjectExtensionDescriptor
 import org.jetbrains.kotlin.analyzer.ModuleInfo
 import org.jetbrains.kotlin.psi.JetFile
 
-public trait ExternalDeclarationsProvider {
+public interface ExternalDeclarationsProvider {
     companion object : ProjectExtensionDescriptor<ExternalDeclarationsProvider>(
             "org.jetbrains.kotlin.externalDeclarationsProvider",
             javaClass<ExternalDeclarationsProvider>()
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/kdoc/psi/api/KDoc.kt b/compiler/frontend/src/org/jetbrains/kotlin/kdoc/psi/api/KDoc.kt
index 4b354b479ce..186a489ef50 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/kdoc/psi/api/KDoc.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/kdoc/psi/api/KDoc.kt
@@ -22,7 +22,7 @@ import org.jetbrains.kotlin.psi.JetDeclaration
 import org.jetbrains.kotlin.kdoc.parser.KDocKnownTag
 
 // Don't implement JetElement (or it will be treated as statement)
-public trait KDoc : PsiComment {
+public interface KDoc : PsiComment {
     public fun getOwner(): JetDeclaration?
     public fun getDefaultSection(): KDocSection
     public fun findSectionByName(name: String): KDocSection?
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/psi/JetQualifiedExpressionImpl.kt b/compiler/frontend/src/org/jetbrains/kotlin/psi/JetQualifiedExpressionImpl.kt
index e10d716a07f..1d15530d9be 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/psi/JetQualifiedExpressionImpl.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/psi/JetQualifiedExpressionImpl.kt
@@ -33,7 +33,7 @@ object JetQualifiedExpressionImpl {
     }
 
     private fun JetQualifiedExpression.getExpression(afterOperation: Boolean): JetExpression? {
-        return getOperationTokenNode()?.getPsi()?.siblings(afterOperation, false)?.firstOrNull { it is JetExpression } as? JetExpression
+        return getOperationTokenNode().getPsi()?.siblings(afterOperation, false)?.firstOrNull { it is JetExpression } as? JetExpression
     }
 
     public fun JetQualifiedExpression.getReceiverExpression(): JetExpression {
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/psi/ValueArgument.kt b/compiler/frontend/src/org/jetbrains/kotlin/psi/ValueArgument.kt
index b28eef1a954..d4ac812f75b 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/psi/ValueArgument.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/psi/ValueArgument.kt
@@ -19,7 +19,7 @@ package org.jetbrains.kotlin.psi
 import com.intellij.psi.impl.source.tree.LeafPsiElement
 import org.jetbrains.kotlin.name.Name
 
-public trait ValueArgument {
+public interface ValueArgument {
     IfNotParsed
     public fun getArgumentExpression(): JetExpression?
 
@@ -36,7 +36,7 @@ public trait ValueArgument {
     public fun isExternal(): Boolean
 }
 
-public trait FunctionLiteralArgument : ValueArgument {
+public interface FunctionLiteralArgument : ValueArgument {
     public fun getFunctionLiteral(): JetFunctionLiteralExpression
 
     override fun getArgumentExpression(): JetExpression
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/AnnotationUtil.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/AnnotationUtil.kt
index 94fbbebc1e6..868d122f7e2 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/AnnotationUtil.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/AnnotationUtil.kt
@@ -50,7 +50,7 @@ private fun CallableDescriptor.isPlatformStaticIn(predicate: (DeclarationDescrip
         when (this) {
             is PropertyAccessorDescriptor -> {
                 val propertyDescriptor = getCorrespondingProperty()
-                predicate(propertyDescriptor.getContainingDeclaration()!!) &&
+                predicate(propertyDescriptor.getContainingDeclaration()) &&
                 (hasPlatformStaticAnnotation() || propertyDescriptor.hasPlatformStaticAnnotation())
             }
             else -> predicate(getContainingDeclaration()) && hasPlatformStaticAnnotation()
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/CodeAnalyzerInitializer.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/CodeAnalyzerInitializer.kt
index f5540fa887d..a87a79fefe7 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/CodeAnalyzerInitializer.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/CodeAnalyzerInitializer.kt
@@ -21,7 +21,7 @@ import com.intellij.openapi.project.Project
 import com.intellij.openapi.components.ServiceManager
 import org.jetbrains.kotlin.descriptors.ModuleDescriptor
 
-public trait CodeAnalyzerInitializer {
+public interface CodeAnalyzerInitializer {
     public fun initialize(trace: BindingTrace, module: ModuleDescriptor, codeAnalyzer: KotlinCodeAnalyzer?)
     public fun createTrace(): BindingTrace
     
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/DescriptorToSourceUtils.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/DescriptorToSourceUtils.kt
index e5512dc68ff..4436d3e17fe 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/DescriptorToSourceUtils.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/DescriptorToSourceUtils.kt
@@ -83,8 +83,8 @@ public object DescriptorToSourceUtils {
         if (declarationDescriptor is PropertyAccessorDescriptor) {
             descriptor = (descriptor as PropertyAccessorDescriptor).getCorrespondingProperty()
         }
-        while (!(descriptor == null || DescriptorUtils.isTopLevelDeclaration(descriptor!!))) {
-            descriptor = descriptor!!.getContainingDeclaration()
+        while (!(descriptor == null || DescriptorUtils.isTopLevelDeclaration(descriptor))) {
+            descriptor = descriptor.getContainingDeclaration()
         }
         return descriptor
     }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/TypeBinding.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/TypeBinding.kt
index a48d5a6b354..13dc2c5eb0d 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/TypeBinding.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/TypeBinding.kt
@@ -28,13 +28,13 @@ import org.jetbrains.kotlin.descriptors.CallableDescriptor
 import org.jetbrains.kotlin.types.TypeProjectionImpl
 
 
-trait TypeBinding<out P : PsiElement> {
+interface TypeBinding<out P : PsiElement> {
     val psiElement: P
     val jetType: JetType
     fun getArgumentBindings(): List<TypeArgumentBinding<P>?>
 }
 
-trait TypeArgumentBinding<out P: PsiElement> {
+interface TypeArgumentBinding<out P: PsiElement> {
     val typeProjection: TypeProjection
     val typeParameterDescriptor: TypeParameterDescriptor?
     val typeBinding: TypeBinding<P>
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/AdditionalTypeChecker.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/AdditionalTypeChecker.kt
index 63433a8efdc..8809c6cab38 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/AdditionalTypeChecker.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/AdditionalTypeChecker.kt
@@ -23,7 +23,7 @@ import org.jetbrains.kotlin.descriptors.ReceiverParameterDescriptor
 import org.jetbrains.kotlin.resolve.scopes.receivers.ReceiverValue
 import org.jetbrains.kotlin.resolve.calls.context.CallResolutionContext
 
-public trait AdditionalTypeChecker {
+public interface AdditionalTypeChecker {
 
     public class Composite(val checkers: List<AdditionalTypeChecker>): AdditionalTypeChecker {
         override fun checkType(expression: JetExpression, expressionType: JetType, c: ResolutionContext<*>) {
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/InlineCheckerWrapper.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/InlineCheckerWrapper.kt
index 2d2a718bf47..54cf17f2bc7 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/InlineCheckerWrapper.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/InlineCheckerWrapper.kt
@@ -33,14 +33,12 @@ public class InlineCheckerWrapper : CallChecker {
         var parentDescriptor: DeclarationDescriptor? = context.scope.getContainingDeclaration()
 
         while (parentDescriptor != null) {
-            val descriptor = parentDescriptor!!
-
-            if (InlineUtil.isInline(descriptor)) {
-                val checker = getChecker(descriptor as SimpleFunctionDescriptor)
+            if (InlineUtil.isInline(parentDescriptor)) {
+                val checker = getChecker(parentDescriptor as SimpleFunctionDescriptor)
                 checker.check(resolvedCall, context)
             }
 
-            parentDescriptor = parentDescriptor?.getContainingDeclaration()
+            parentDescriptor = parentDescriptor.getContainingDeclaration()
         }
     }
 
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/context/ResolutionResultsCache.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/context/ResolutionResultsCache.kt
index 66e343ad68b..08d34665e13 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/context/ResolutionResultsCache.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/context/ResolutionResultsCache.kt
@@ -24,7 +24,7 @@ import org.jetbrains.kotlin.psi.Call
 import org.jetbrains.kotlin.resolve.calls.tasks.TracingStrategy
 import org.jetbrains.kotlin.resolve.calls.context.ResolutionResultsCache.CachedData
 
-public trait ResolutionResultsCache {
+public interface ResolutionResultsCache {
     public data class CachedData(
             val resolutionResults: OverloadResolutionResultsImpl<*>,
             val deferredComputation: BasicCallResolutionContext,
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/model/ArgumentMapping.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/model/ArgumentMapping.kt
index 39caf37c688..57a13ca7bd5 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/model/ArgumentMapping.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/model/ArgumentMapping.kt
@@ -38,7 +38,7 @@ public enum class ArgumentMatchStatus(val isError: Boolean = true) {
     UNKNOWN()
 }
 
-public trait ArgumentMatch : ArgumentMapping {
+public interface ArgumentMatch : ArgumentMapping {
     public val valueParameter: ValueParameterDescriptor
     public val status: ArgumentMatchStatus
 
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/model/VariableAsFunctionResolvedCall.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/model/VariableAsFunctionResolvedCall.kt
index 119000225e6..31db54d9bd8 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/model/VariableAsFunctionResolvedCall.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/model/VariableAsFunctionResolvedCall.kt
@@ -21,7 +21,7 @@ import org.jetbrains.kotlin.descriptors.VariableDescriptor
 import org.jetbrains.kotlin.resolve.calls.results.ResolutionStatus
 import org.jetbrains.kotlin.resolve.DelegatingBindingTrace
 
-public trait VariableAsFunctionResolvedCall {
+public interface VariableAsFunctionResolvedCall {
     public val functionCall: ResolvedCall<FunctionDescriptor>
     public val variableCall: ResolvedCall<VariableDescriptor>
 }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tasks/CallableDescriptorCollectors.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tasks/CallableDescriptorCollectors.kt
index 2625c5d35de..5f27d80f715 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tasks/CallableDescriptorCollectors.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tasks/CallableDescriptorCollectors.kt
@@ -31,7 +31,7 @@ import org.jetbrains.kotlin.types.ErrorUtils
 import org.jetbrains.kotlin.types.JetType
 import org.jetbrains.kotlin.types.expressions.OperatorConventions
 
-public trait CallableDescriptorCollector<D : CallableDescriptor> {
+public interface CallableDescriptorCollector<D : CallableDescriptor> {
 
     public fun getNonExtensionsByName(scope: JetScope, name: Name, bindingTrace: BindingTrace): Collection<D>
 
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tasks/ResolutionTaskHolder.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tasks/ResolutionTaskHolder.kt
index edafbdb4cd4..70e23a65651 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tasks/ResolutionTaskHolder.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tasks/ResolutionTaskHolder.kt
@@ -67,7 +67,7 @@ public class ResolutionTaskHolder<D : CallableDescriptor, F : D>(
         return internalTasks!!
     }
 
-    public trait PriorityProvider<D> {
+    public interface PriorityProvider<D> {
         public fun getPriority(candidate: D): Int
 
         public fun getMaxPriority(): Int
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/diagnostics/Diagnostics.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/diagnostics/Diagnostics.kt
index a14056e7678..f5057120367 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/diagnostics/Diagnostics.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/diagnostics/Diagnostics.kt
@@ -20,7 +20,7 @@ import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.diagnostics.Diagnostic
 import com.intellij.openapi.util.ModificationTracker
 
-public trait Diagnostics : Iterable<Diagnostic> {
+public interface Diagnostics : Iterable<Diagnostic> {
     //should not be called on readonly views
     //any Diagnostics object returned by BindingContext#getDiagnostics() should implement this property
     public val modificationTracker: ModificationTracker
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/LazyClassContext.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/LazyClassContext.kt
index 1bf4105b137..b890d2007d8 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/LazyClassContext.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/LazyClassContext.kt
@@ -21,7 +21,7 @@ import org.jetbrains.kotlin.resolve.*
 import org.jetbrains.kotlin.resolve.lazy.declarations.DeclarationProviderFactory
 import org.jetbrains.kotlin.storage.StorageManager
 
-public trait LazyClassContext {
+public interface LazyClassContext {
     val declarationScopeProvider: DeclarationScopeProvider
 
     val storageManager: StorageManager
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/LazyImportScope.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/LazyImportScope.kt
index 8b2d59de4f0..0093a919144 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/LazyImportScope.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/LazyImportScope.kt
@@ -35,9 +35,8 @@ import org.jetbrains.kotlin.types.JetType
 import org.jetbrains.kotlin.util.collectionUtils.concat
 import org.jetbrains.kotlin.utils.Printer
 import java.util.LinkedHashSet
-import kotlin.properties.Delegates
 
-trait IndexedImports {
+interface IndexedImports {
     val imports: List<JetImportDirective>
     fun importsForName(name: Name): Collection<JetImportDirective>
 }
@@ -50,7 +49,7 @@ class AllUnderImportsIndexed(allImports: Collection<JetImportDirective>) : Index
 class AliasImportsIndexed(allImports: Collection<JetImportDirective>) : IndexedImports {
     override val imports = allImports.filter { !it.isAllUnder() }
 
-    private val nameToDirectives: ListMultimap<Name, JetImportDirective> by Delegates.lazy {
+    private val nameToDirectives: ListMultimap<Name, JetImportDirective> by lazy {
         val builder = ImmutableListMultimap.builder<Name, JetImportDirective>()
 
         for (directive in imports) {
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/ResolveSession.java b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/ResolveSession.java
index eac97c6719c..45358ac7b8f 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/ResolveSession.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/ResolveSession.java
@@ -144,6 +144,7 @@ public class ResolveSession implements KotlinCodeAnalyzer, LazyClassContext {
 
         this.packages =
                 storageManager.createMemoizedFunctionWithNullableValues(new Function1<FqName, LazyPackageDescriptor>() {
+                    @Override
                     @Nullable
                     public LazyPackageDescriptor invoke(FqName fqName) {
                         return createPackage(fqName);
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/TopLevelDescriptorProvider.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/TopLevelDescriptorProvider.kt
index be578e44e37..46d65407d75 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/TopLevelDescriptorProvider.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/TopLevelDescriptorProvider.kt
@@ -22,7 +22,7 @@ import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.psi.JetScript
 import org.jetbrains.kotlin.resolve.lazy.descriptors.LazyPackageDescriptor
 
-public trait TopLevelDescriptorProvider {
+public interface TopLevelDescriptorProvider {
     fun getPackageFragment(fqName: FqName): LazyPackageDescriptor?
 
     fun getScriptDescriptor(script: JetScript): ScriptDescriptor
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/ClassMemberDeclarationProvider.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/ClassMemberDeclarationProvider.kt
index c9c4b39aff0..47ddc75405e 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/ClassMemberDeclarationProvider.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/ClassMemberDeclarationProvider.kt
@@ -18,6 +18,6 @@ package org.jetbrains.kotlin.resolve.lazy.declarations
 
 import org.jetbrains.kotlin.resolve.lazy.data.JetClassLikeInfo
 
-public trait ClassMemberDeclarationProvider : DeclarationProvider {
+public interface ClassMemberDeclarationProvider : DeclarationProvider {
     public fun getOwnerInfo(): JetClassLikeInfo
 }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/DeclarationProvider.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/DeclarationProvider.kt
index 97789132168..034f6854b20 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/DeclarationProvider.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/DeclarationProvider.kt
@@ -23,7 +23,7 @@ import org.jetbrains.kotlin.resolve.lazy.data.JetClassLikeInfo
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.scopes.DescriptorKindFilter
 
-public trait DeclarationProvider {
+public interface DeclarationProvider {
     public fun getDeclarations(kindFilter: DescriptorKindFilter, nameFilter: (Name) -> Boolean): List<JetDeclaration>
 
     public fun getFunctionDeclarations(name: Name): Collection<JetNamedFunction>
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/PackageMemberDeclarationProvider.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/PackageMemberDeclarationProvider.kt
index c87db23831a..627f346ea18 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/PackageMemberDeclarationProvider.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/PackageMemberDeclarationProvider.kt
@@ -21,10 +21,7 @@ import org.jetbrains.kotlin.psi.JetFile
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 
-public trait PackageMemberDeclarationProvider : DeclarationProvider {
-    /**
-     * Implementation of this method are not obliged to use the filters but may do so when it gives any performance advantage
-     */
+public interface PackageMemberDeclarationProvider : DeclarationProvider {
     public fun getAllDeclaredSubPackages(nameFilter: (Name) -> Boolean): Collection<FqName>
 
     public fun getPackageFiles(): Collection<JetFile>
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyClassMemberScope.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyClassMemberScope.kt
index 281951e026c..99ef7bf309e 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyClassMemberScope.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyClassMemberScope.kt
@@ -83,7 +83,7 @@ public open class LazyClassMemberScope(
         return result
     }
 
-    private trait MemberExtractor<T : CallableMemberDescriptor> {
+    private interface MemberExtractor<T : CallableMemberDescriptor> {
         public fun extract(extractFrom: JetType, name: Name): Collection<T>
     }
 
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/scopes/WritableScope.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/scopes/WritableScope.kt
index 69225fe4c70..1bb532b9205 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/scopes/WritableScope.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/scopes/WritableScope.kt
@@ -20,7 +20,7 @@ import com.google.common.collect.Multimap
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.name.Name
 
-public trait WritableScope : JetScope {
+public interface WritableScope : JetScope {
     public enum class LockLevel {
         WRITING,
         BOTH,
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/scopes/receivers/Qualifier.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/scopes/receivers/Qualifier.kt
index ade9e49fdcc..a945b62d5fd 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/scopes/receivers/Qualifier.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/scopes/receivers/Qualifier.kt
@@ -42,7 +42,7 @@ import org.jetbrains.kotlin.utils.addIfNotNull
 import java.util.ArrayList
 import kotlin.properties.Delegates
 
-public trait Qualifier: ReceiverValue {
+public interface Qualifier: ReceiverValue {
 
     public val expression: JetExpression
 
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/source/PsiSourceElement.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/source/PsiSourceElement.kt
index 982200e972f..f211e5c19ce 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/source/PsiSourceElement.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/source/PsiSourceElement.kt
@@ -19,6 +19,6 @@ package org.jetbrains.kotlin.resolve.source
 import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.descriptors.SourceElement
 
-public trait PsiSourceElement : SourceElement {
+public interface PsiSourceElement : SourceElement {
     public val psi: PsiElement?
 }
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/validation/SymbolUsageValidator.kt b/compiler/frontend/src/org/jetbrains/kotlin/resolve/validation/SymbolUsageValidator.kt
index 8dd87fd7486..89cd16d67e8 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/validation/SymbolUsageValidator.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/validation/SymbolUsageValidator.kt
@@ -22,7 +22,7 @@ import org.jetbrains.kotlin.descriptors.ClassifierDescriptor
 import org.jetbrains.kotlin.resolve.BindingTrace
 import kotlin.platform.platformStatic
 
-public trait SymbolUsageValidator {
+public interface SymbolUsageValidator {
 
     public fun validateTypeUsage(targetDescriptor: ClassifierDescriptor, trace: BindingTrace, element: PsiElement) { }
 
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/ExpressionTypingVisitorDispatcher.java b/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/ExpressionTypingVisitorDispatcher.java
index 586ec8986e4..6be683dc526 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/ExpressionTypingVisitorDispatcher.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/types/expressions/ExpressionTypingVisitorDispatcher.java
@@ -307,6 +307,7 @@ public class ExpressionTypingVisitorDispatcher extends JetVisitor<JetTypeInfo, E
 
 //////////////////////////////////////////////////////////////////////////////////////////////
 
+    @Override
     public JetTypeInfo visitSimpleNameExpression(@NotNull JetSimpleNameExpression expression, ExpressionTypingContext data) {
         return basic.visitSimpleNameExpression(expression, data);
     }