[KT-59294] [wasm] Resolve undefined to null for any nullable types in external functions

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

@@ -328,14 +328,10 @@ class JsInteropFunctionsLowering(val context: WasmBackendContext) : DeclarationT
             )
         } else { //nullable reference should not be checked
             val nullableValueAdapter = valueAdapter?.let(::NullOrAdapter)
-            if (isExternalType(notNullType)) {
+            val undefinedToNullAdapter = FunctionBasedAdapter(adapters.jsCheckIsNullOrUndefinedAdapter.owner)
-                val undefinedToNullAdapter = FunctionBasedAdapter(adapters.jsCheckIsNullOrUndefinedAdapter.owner)
+            nullableValueAdapter
-                nullableValueAdapter
+                ?.let { CombineAdapter(it, undefinedToNullAdapter) }
-                    ?.let { CombineAdapter(it, undefinedToNullAdapter) }
+                ?: undefinedToNullAdapter
-                    ?: undefinedToNullAdapter
-            } else {
-                nullableValueAdapter
-            }
         }
     }
 

compiler/testData/codegen/boxWasmJsInterop/nullableExternRefs.kt

@@ -25,6 +25,10 @@ fun getNull(): EI? =
 fun getUndefined(): EI? =
     js("undefined")
 
+// https://youtrack.jetbrains.com/issue/KT-59294/WASM-localStorage-Cannot-read-properties-of-undefined-reading-length
+fun getStringUndefined(): String? =
+    js("undefined")
+
 fun isJsNull(ref: EI?): Boolean =
     js("ref === null")
 
@@ -55,6 +59,7 @@ fun box(): String {
     assertTrue((jsNull as Any?) == null)
     assertTrue((jsNull as Any?) === null)
     assertTrue(jsUndefined == null)
+    assertTrue(getStringUndefined() == null)
 
     assertTrue(isJsNull(null))
     assertTrue(isJsNull(null as EI?))

js/js.translator/testData/box/native/simpleUndefined.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: WASM
 // EXPECTED_REACHABLE_NODES: 1281
 package foo