diff --git a/compiler/testData/diagnostics/tests/j+k/types/arrayList.kt b/compiler/testData/diagnostics/tests/j+k/types/arrayList.kt
index 107e4068059..6e405cc393e 100644
--- a/compiler/testData/diagnostics/tests/j+k/types/arrayList.kt
+++ b/compiler/testData/diagnostics/tests/j+k/types/arrayList.kt
@@ -1,6 +1,6 @@
 // FILE: k.kt
 
-trait ML<T> {
+interface ML<T> {
     public fun foo(): MutableList<T>
 }
 
diff --git a/compiler/testData/diagnostics/tests/j+k/types/arrayList.txt b/compiler/testData/diagnostics/tests/j+k/types/arrayList.txt
index 36f1fa464ad..793d26b1e99 100644
--- a/compiler/testData/diagnostics/tests/j+k/types/arrayList.txt
+++ b/compiler/testData/diagnostics/tests/j+k/types/arrayList.txt
@@ -16,7 +16,7 @@ internal final class K : J<kotlin.String>, ML<kotlin.String> {
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
-internal trait ML</*0*/ T> {
+internal interface ML</*0*/ T> {
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public abstract fun foo(): kotlin.MutableList<T>
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
diff --git a/compiler/testData/diagnostics/tests/j+k/types/returnCollection.kt b/compiler/testData/diagnostics/tests/j+k/types/returnCollection.kt
index 84e5a4b8eb8..4ead28c1794 100644
--- a/compiler/testData/diagnostics/tests/j+k/types/returnCollection.kt
+++ b/compiler/testData/diagnostics/tests/j+k/types/returnCollection.kt
@@ -1,6 +1,6 @@
 // FILE: k.kt
 
-trait K {
+interface K {
     fun foo(): List<String>
 }
 
diff --git a/compiler/testData/diagnostics/tests/j+k/types/returnCollection.txt b/compiler/testData/diagnostics/tests/j+k/types/returnCollection.txt
index d918d8c2f36..198fd3c2834 100644
--- a/compiler/testData/diagnostics/tests/j+k/types/returnCollection.txt
+++ b/compiler/testData/diagnostics/tests/j+k/types/returnCollection.txt
@@ -2,14 +2,14 @@ package
 
 public/*package*/ /*synthesized*/ fun J(/*0*/ function: () -> kotlin.(Mutable)List<kotlin.String!>!): J
 
-public/*package*/ trait J : K {
+public/*package*/ interface J : K {
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public abstract override /*1*/ fun foo(): kotlin.List<kotlin.String>
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
-internal trait K {
+internal interface K {
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     internal abstract fun foo(): kotlin.List<kotlin.String>
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
diff --git a/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPosition.kt b/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPosition.kt
index 33a4d10347f..84c8934b225 100644
--- a/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPosition.kt
+++ b/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPosition.kt
@@ -1,9 +1,9 @@
 // FILE: k.kt
 
-trait G<T>
-trait SubG : G<String>
+interface G<T>
+interface SubG : G<String>
 
-trait K {
+interface K {
     fun foo(): G<String>
     fun bar(): G<String>?
 }
diff --git a/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPosition.txt b/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPosition.txt
index 514a4497b84..36ae41d1de9 100644
--- a/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPosition.txt
+++ b/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPosition.txt
@@ -1,12 +1,12 @@
 package
 
-internal trait G</*0*/ T> {
+internal interface G</*0*/ T> {
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
-public/*package*/ trait J : K {
+public/*package*/ interface J : K {
     public abstract override /*1*/ fun bar(): SubG?
     public abstract fun baz(): SubG!
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
@@ -15,7 +15,7 @@ public/*package*/ trait J : K {
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
-internal trait K {
+internal interface K {
     internal abstract fun bar(): G<kotlin.String>?
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     internal abstract fun foo(): G<kotlin.String>
@@ -23,7 +23,7 @@ internal trait K {
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
-internal trait SubG : G<kotlin.String> {
+internal interface SubG : G<kotlin.String> {
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
diff --git a/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPositionGeneric.kt b/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPositionGeneric.kt
index e07ec6ec4b3..2ab572dca5a 100644
--- a/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPositionGeneric.kt
+++ b/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPositionGeneric.kt
@@ -1,9 +1,9 @@
 // FILE: k.kt
 
-trait G<T>
-trait SubG<A, B> : G<String>
+interface G<T>
+interface SubG<A, B> : G<String>
 
-trait K<KT> {
+interface K<KT> {
     fun foo(): G<KT>
     fun bar(): G<KT>?
 }
diff --git a/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPositionGeneric.txt b/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPositionGeneric.txt
index 5927cab9c4c..84f01f74142 100644
--- a/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPositionGeneric.txt
+++ b/compiler/testData/diagnostics/tests/j+k/types/shapeMismatchInCovariantPositionGeneric.txt
@@ -1,12 +1,12 @@
 package
 
-internal trait G</*0*/ T> {
+internal interface G</*0*/ T> {
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
-public/*package*/ trait J : K<kotlin.String!> {
+public/*package*/ interface J : K<kotlin.String!> {
     public abstract override /*1*/ fun bar(): SubG<kotlin.String!, G<kotlin.String!>!>?
     public abstract fun baz(): SubG<kotlin.String!, G<kotlin.String!>!>!
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
@@ -15,7 +15,7 @@ public/*package*/ trait J : K<kotlin.String!> {
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
-internal trait K</*0*/ KT> {
+internal interface K</*0*/ KT> {
     internal abstract fun bar(): G<KT>?
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     internal abstract fun foo(): G<KT>
@@ -23,7 +23,7 @@ internal trait K</*0*/ KT> {
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
-internal trait SubG</*0*/ A, /*1*/ B> : G<kotlin.String> {
+internal interface SubG</*0*/ A, /*1*/ B> : G<kotlin.String> {
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
diff --git a/compiler/testData/diagnostics/tests/j+k/types/typeParameter.kt b/compiler/testData/diagnostics/tests/j+k/types/typeParameter.kt
index 3aac76a2aad..550b69b506d 100644
--- a/compiler/testData/diagnostics/tests/j+k/types/typeParameter.kt
+++ b/compiler/testData/diagnostics/tests/j+k/types/typeParameter.kt
@@ -1,6 +1,6 @@
 // FILE: k.kt
 
-trait K {
+interface K {
     fun <T> foo(t: T)
 }
 
diff --git a/compiler/testData/diagnostics/tests/j+k/types/typeParameter.txt b/compiler/testData/diagnostics/tests/j+k/types/typeParameter.txt
index 836bc55a09d..d96e7b10deb 100644
--- a/compiler/testData/diagnostics/tests/j+k/types/typeParameter.txt
+++ b/compiler/testData/diagnostics/tests/j+k/types/typeParameter.txt
@@ -1,13 +1,13 @@
 package
 
-public/*package*/ trait J : K {
+public/*package*/ interface J : K {
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public abstract override /*1*/ fun </*0*/ T> foo(/*0*/ t: T): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
-internal trait K {
+internal interface K {
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     internal abstract fun </*0*/ T> foo(/*0*/ t: T): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
diff --git a/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/delegatedProperties.txt b/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/delegatedProperties.txt
index c254131e578..8861f67a667 100644
--- a/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/delegatedProperties.txt
+++ b/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/delegatedProperties.txt
@@ -10,7 +10,7 @@ public open class J {
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 
-    public trait DP {
+    public interface DP {
         public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
         public abstract fun get(/*0*/ a: kotlin.Any!, /*1*/ b: kotlin.Any!): kotlin.String!
         public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
diff --git a/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/invoke.txt b/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/invoke.txt
index 12dc37e9833..2c0af6f063f 100644
--- a/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/invoke.txt
+++ b/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/invoke.txt
@@ -8,7 +8,7 @@ public open class J {
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 
-    public trait Invoke {
+    public interface Invoke {
         public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
         public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
         public abstract fun invoke(): kotlin.Unit
diff --git a/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/multiDeclaration.txt b/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/multiDeclaration.txt
index 6d630b5f0e1..5c7644e6642 100644
--- a/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/multiDeclaration.txt
+++ b/compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/multiDeclaration.txt
@@ -8,7 +8,7 @@ public open class J {
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 
-    public trait Multi {
+    public interface Multi {
         public abstract fun component1(): kotlin.String!
         public abstract fun component2(): kotlin.String!
         public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean