[Wasm] Fix access to WebIDL dictionary members

Evaluate external interface companion objects as an empty JS object
instead of null due to null checks on interop boundary.

^KT-59082 Fixed

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/lower/ComplexExternalDeclarationsToTopLevelFunctionsLowering.kt

@@ -156,6 +156,27 @@ class ComplexExternalDeclarationsToTopLevelFunctionsLowering(val context: WasmBa
     private fun StringBuilder.appendExternalClassReference(klass: IrClass) {
         val parent = klass.parent
         if (parent is IrClass) {
+
+            // This is hack to support Kotlin/JS like implementation of IDL string enums bindings
+            // with error suppression:
+            //
+            //    @JsName("null")
+            //    @Suppress("NESTED_CLASS_IN_EXTERNAL_INTERFACE")
+            //    public external interface CanvasFillRule {
+            //        companion object
+            //    }
+            //    public inline val CanvasFillRule.Companion.NONZERO: CanvasFillRule get() = "nonzero".asDynamic().unsafeCast<CanvasFillRule>()
+            //
+            // Kotlin/JS translates access to CanvasFillRule.Companion as `null` due to @JsName("null"),
+            // but Kotlin/Wasm fails to do this due to stricter null checks on interop boundary.
+            //
+            // Instead, as a temporary solution, we evaluate such companion object to an empty JS object.
+            // TODO: Optimize (KT-60661)
+            if (parent.isInterface) {
+                append("({})")
+                return
+            }
+
             appendExternalClassReference(parent)
             if (klass.isCompanion) {
                 // Reference to external companion object is reference to its parent class

compiler/testData/codegen/boxWasmJsInterop/kt59082.kt

@@ -0,0 +1,15 @@
+// TARGET_BACKEND: WASM
+
+@JsName("null")
+@Suppress("NESTED_CLASS_IN_EXTERNAL_INTERFACE")
+public external interface CanvasFillRule : JsAny {
+    companion object
+}
+
+public inline val CanvasFillRule.Companion.EVENODD: CanvasFillRule get() =
+    "evenodd".toJsString().unsafeCast<CanvasFillRule>()
+
+fun box(): String {
+    if (CanvasFillRule.EVENODD.toString() != "evenodd") return "Fail 1"
+    return "OK"
+}

wasm/wasm.tests/tests-gen/org/jetbrains/kotlin/wasm/test/FirWasmCodegenWasmJsInteropTestGenerated.java

@@ -115,6 +115,12 @@ public class FirWasmCodegenWasmJsInteropTestGenerated extends AbstractFirWasmCod
         runTest("compiler/testData/codegen/boxWasmJsInterop/kotlinToJsAdapters.kt");
     }
 
+    @Test
+    @TestMetadata("kt59082.kt")
+    public void testKt59082() throws Exception {
+        runTest("compiler/testData/codegen/boxWasmJsInterop/kt59082.kt");
+    }
+
     @Test
     @TestMetadata("lambdaAdapterNameClash.kt")
     public void testLambdaAdapterNameClash() throws Exception {

wasm/wasm.tests/tests-gen/org/jetbrains/kotlin/wasm/test/K1WasmCodegenWasmJsInteropTestGenerated.java

@@ -115,6 +115,12 @@ public class K1WasmCodegenWasmJsInteropTestGenerated extends AbstractK1WasmCodeg
         runTest("compiler/testData/codegen/boxWasmJsInterop/kotlinToJsAdapters.kt");
     }
 
+    @Test
+    @TestMetadata("kt59082.kt")
+    public void testKt59082() throws Exception {
+        runTest("compiler/testData/codegen/boxWasmJsInterop/kt59082.kt");
+    }
+
     @Test
     @TestMetadata("lambdaAdapterNameClash.kt")
     public void testLambdaAdapterNameClash() throws Exception {