[JS] Keep interfaces

^KT-54173 fixed

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/dce/JsUsefulDeclarationProcessor.kt

@@ -127,7 +127,8 @@ internal class JsUsefulDeclarationProcessor(
 
     override fun processSuperTypes(irClass: IrClass) {
         irClass.superTypes.forEach {
-            if (!it.isInterface()) {
+            val shouldClassBeKept = it.classOrNull?.let { context.keeper.shouldKeep(it.owner) } ?: false
+            if (!it.isInterface() || shouldClassBeKept) {
                 (it.classifierOrNull as? IrClassSymbol)?.owner?.enqueue(irClass, "superTypes")
             }
         }

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/dce/UselessDeclarationsRemover.kt

@@ -63,7 +63,7 @@ class UselessDeclarationsRemover(
 
     private fun IrClassSymbol.collectUsedSuperTypes(): Set<IrClassSymbol> {
         return savedTypesCache.getOrPut(this) {
-            if (owner in usefulDeclarations) {
+            if (owner in usefulDeclarations || context.keeper.shouldKeep(owner)) {
                 setOf(this)
             } else {
                 owner.superTypes

js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/ir/FirJsTestGenerated.java

@@ -7290,6 +7290,12 @@ public class FirJsTestGenerated extends AbstractFirJsTest {
             runTest("js/js.translator/testData/box/keep/keepClass.kt");
         }
 
+        @Test
+        @TestMetadata("keepInterface.kt")
+        public void testKeepInterface() throws Exception {
+            runTest("js/js.translator/testData/box/keep/keepInterface.kt");
+        }
+
         @Test
         @TestMetadata("keepMethod.kt")
         public void testKeepMethod() throws Exception {
@@ -7313,6 +7319,12 @@ public class FirJsTestGenerated extends AbstractFirJsTest {
         public void testKeepOverriddenMethod() throws Exception {
             runTest("js/js.translator/testData/box/keep/keepOverriddenMethod.kt");
         }
+
+        @Test
+        @TestMetadata("keepVarAnonymousClass.kt")
+        public void testKeepVarAnonymousClass() throws Exception {
+            runTest("js/js.translator/testData/box/keep/keepVarAnonymousClass.kt");
+        }
     }
 
     @Nested

js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/ir/IrBoxJsTestGenerated.java

@@ -7290,6 +7290,12 @@ public class IrBoxJsTestGenerated extends AbstractIrBoxJsTest {
             runTest("js/js.translator/testData/box/keep/keepClass.kt");
         }
 
+        @Test
+        @TestMetadata("keepInterface.kt")
+        public void testKeepInterface() throws Exception {
+            runTest("js/js.translator/testData/box/keep/keepInterface.kt");
+        }
+
         @Test
         @TestMetadata("keepMethod.kt")
         public void testKeepMethod() throws Exception {
@@ -7313,6 +7319,12 @@ public class IrBoxJsTestGenerated extends AbstractIrBoxJsTest {
         public void testKeepOverriddenMethod() throws Exception {
             runTest("js/js.translator/testData/box/keep/keepOverriddenMethod.kt");
         }
+
+        @Test
+        @TestMetadata("keepVarAnonymousClass.kt")
+        public void testKeepVarAnonymousClass() throws Exception {
+            runTest("js/js.translator/testData/box/keep/keepVarAnonymousClass.kt");
+        }
     }
 
     @Nested

js/js.translator/testData/box/keep/keepInterface.kt

@@ -0,0 +1,34 @@
+// TARGET_BACKEND: JS_IR
+// ONLY_IR_DCE
+// RUN_PLAIN_BOX_FUNCTION
+// INFER_MAIN_MODULE
+// KEEP: DenotedFace
+
+// MODULE: keep_interface
+// FILE: lib.kt
+
+interface DenotedFace {
+    fun keepMeA() = 7
+    fun keepMeB(): Int
+}
+
+class A : DenotedFace {
+    override fun keepMeB(): Int {
+        return 8
+    }
+}
+
+@JsExport
+fun foo(): A {
+    return A()
+}
+
+// FILE: test.js
+function box() {
+    var a = this["keep_interface"].foo()
+
+    if (a.keepMeA_ds0nq4_k$() != 7) return "fail 1"
+    if (a.keepMeB_ds0nq3_k$() != 8) return "fail 2"
+
+    return "OK"
+}

js/js.translator/testData/box/keep/keepVarAnonymousClass.kt

@@ -0,0 +1,26 @@
+// TARGET_BACKEND: JS_IR
+// ONLY_IR_DCE
+// RUN_PLAIN_BOX_FUNCTION
+// INFER_MAIN_MODULE
+// KEEP: DenotedFace
+
+// MODULE: keep_var
+// FILE: lib.kt
+
+interface DenotedFace {
+    fun keepMeA() = 7
+    fun keepMeB(): Int
+}
+
+@JsExport
+val denotedFaceTrigger = object : DenotedFace { override fun keepMeB() = 8 }
+
+// FILE: test.js
+function box() {
+    var a = this["keep_var"].denotedFaceTrigger
+
+    if (a.keepMeA_ds0nq4_k$() != 7) return "fail 1"
+    if (a.keepMeB_ds0nq3_k$() != 8) return "fail 2"
+
+    return "OK"
+}