[JS] Forbid export of interfaces

With the only exception of external interfaces.

See https://youtrack.jetbrains.com/issue/KT-44099

compiler/testData/diagnostics/testsWithJsStdLib/export/extendingNonExportedType.kt

@@ -20,7 +20,7 @@ open class ExportedGenericClass<T>
 class <!NON_EXPORTABLE_TYPE("super; ExportedGenericClass<NonExportedClass>")!>ExportedClass3<!> : ExportedGenericClass<NonExportedClass>()
 
 @JsExport
-interface ExportedGenericInterface<T>
+interface <!WRONG_EXPORTED_DECLARATION!>ExportedGenericInterface<!><T>
 
 @JsExport
 class <!NON_EXPORTABLE_TYPE("super; ExportedGenericInterface<NonExportedClass>")!>ExportedClass4<!> : ExportedGenericInterface<NonExportedClass>

compiler/testData/diagnostics/testsWithJsStdLib/export/unexportableTypesInTypeParameters.kt

@@ -14,4 +14,4 @@ fun <<!NON_EXPORTABLE_TYPE("upper bound; C")!>T : C<!>>foo() { }
 class A<<!NON_EXPORTABLE_TYPE("upper bound; C")!>T : C<!>, <!NON_EXPORTABLE_TYPE("upper bound; I")!>S: I<!>>
 
 @JsExport
-interface I2<<!NON_EXPORTABLE_TYPE("upper bound; C"), NON_EXPORTABLE_TYPE("upper bound; I")!>T<!>> where T : C, T : I
+interface <!WRONG_EXPORTED_DECLARATION!>I2<!><<!NON_EXPORTABLE_TYPE("upper bound; C"), NON_EXPORTABLE_TYPE("upper bound; I")!>T<!>> where T : C, T : I

compiler/testData/diagnostics/testsWithJsStdLib/export/wrongExportedDeclaration.kt

@@ -18,3 +18,9 @@ enum class <!WRONG_EXPORTED_DECLARATION("enum class")!>EnumClass<!> { ENTRY1, EN
 
 @JsExport
 annotation class <!WRONG_EXPORTED_DECLARATION("annotation class")!>AnnotationClass<!>
+
+@JsExport
+interface <!WRONG_EXPORTED_DECLARATION("interface")!>SomeInterface<!>
+
+@JsExport
+external interface GoodInterface

compiler/testData/diagnostics/testsWithJsStdLib/export/wrongExportedDeclaration.txt

@@ -30,4 +30,16 @@ package foo {
         public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): foo.EnumClass
         public final /*synthesized*/ fun values(): kotlin.Array<foo.EnumClass>
     }
+
+    @kotlin.js.JsExport public external interface GoodInterface {
+        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
+    }
+
+    @kotlin.js.JsExport public interface SomeInterface {
+        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
+    }
 }

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsExportDeclarationChecker.kt

@@ -107,14 +107,18 @@ object JsExportDeclarationChecker : DeclarationChecker {
                     checkTypeParameter(typeParameter)
                 }
 
-                if (descriptor.kind == ENUM_CLASS) {
-                    reportWrongExportedDeclaration("enum class")
-                    return
-                }
-                if (descriptor.kind == ANNOTATION_CLASS) {
-                    reportWrongExportedDeclaration("annotation class")
+                val wrongDeclaration: String? = when (descriptor.kind) {
+                    ENUM_CLASS -> "enum class"
+                    INTERFACE -> if (descriptor.isExternal) null else "interface"
+                    ANNOTATION_CLASS -> "annotation class"
+                    else -> null
+                }
+
+                if (wrongDeclaration != null) {
+                    reportWrongExportedDeclaration(wrongDeclaration)
                     return
                 }
+
                 if (descriptor.kind == ENUM_ENTRY) {
                     // Covered by ENUM_CLASS
                     return

js/js.translator/testData/box/inline/inlinedObjectLiteralIsCheck.kt

@@ -1,6 +1,5 @@
 // EXPECTED_REACHABLE_NODES: 1282
 
-@JsExport
 interface I {
     fun ok(): String
 }