[Wasm] Imporove external interface support

* Support boxing/unboxing when casting to Any
* Support ===, equals, hashCode, toString

* Support adapting String in interop boundary

.idea/artifacts/kotlin_test_wasm_js_1_6_255_SNAPSHOT.xml

@@ -1,6 +1,8 @@
 <component name="ArtifactManager">
   <artifact type="jar" name="kotlin-test-wasm-js-1.6.255-SNAPSHOT">
     <output-path>$PROJECT_DIR$/libraries/kotlin.test/wasm/build/libs</output-path>
-    <root id="archive" name="kotlin-test-wasm-js-1.6.255-SNAPSHOT.jar" />
+    <root id="archive" name="kotlin-test-wasm-js-1.6.255-SNAPSHOT.jar">
+      <element id="module-output" name="kotlin.kotlin-test.kotlin-test-wasm.jsMain" />
+    </root>
   </artifact>
 </component>

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmBackendContext.kt

@@ -35,7 +35,6 @@ class WasmBackendContext(
     override val irBuiltIns: IrBuiltIns,
     symbolTable: SymbolTable,
     irModuleFragment: IrModuleFragment,
-    val additionalExportedDeclarations: Set<FqName>,
     override val configuration: CompilerConfiguration,
 ) : JsCommonBackendContext {
     override val builtIns = module.builtIns

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmLoweringPhases.kt

@@ -66,7 +66,7 @@ private val expectDeclarationsRemovingPhase = makeWasmModulePhase(
     description = "Remove expect declaration from module fragment"
 )
 
-private val stringConstructorLowering = makeWasmModulePhase(
+private val stringConcatenationLowering = makeWasmModulePhase(
     ::StringConcatenationLowering,
     name = "StringConcatenation",
     description = "String concatenation lowering"
@@ -122,6 +122,18 @@ private val tailrecLoweringPhase = makeWasmModulePhase(
     description = "Replace `tailrec` call sites with equivalent loop"
 )
 
+private val jsInteropFunctionsLowering = makeWasmModulePhase(
+    ::JsInteropFunctionsLowering,
+    name = "JsInteropFunctionsLowering",
+    description = "Create delegates for JS interop",
+)
+
+private val jsInteropFunctionCallsLowering = makeWasmModulePhase(
+    ::JsInteropFunctionCallsLowering,
+    name = "JsInteropFunctionCallsLowering",
+    description = "Replace calls to delegates",
+)
+
 private val enumClassConstructorLoweringPhase = makeWasmModulePhase(
     ::EnumClassConstructorLowering,
     name = "EnumClassConstructorLowering",
@@ -134,7 +146,6 @@ private val enumClassConstructorBodyLoweringPhase = makeWasmModulePhase(
     description = "Transform Enum Class into regular Class"
 )
 
-
 private val enumEntryInstancesLoweringPhase = makeWasmModulePhase(
     ::EnumEntryInstancesLowering,
     name = "EnumEntryInstancesLowering",
@@ -431,6 +442,12 @@ private val objectUsageLoweringPhase = makeWasmModulePhase(
     description = "Transform IrGetObjectValue into instance generator call"
 )
 
+private val explicitlyCastExternalTypesPhase = makeWasmModulePhase(
+    ::ExplicitlyCastExternalTypesLowering,
+    name = "ExplicitlyCastExternalTypesLowering",
+    description = "Add explicit casts when converting between external and non-external types"
+)
+
 private val typeOperatorLoweringPhase = makeWasmModulePhase(
     ::WasmTypeOperatorLowering,
     name = "TypeOperatorLowering",
@@ -515,6 +532,9 @@ val wasmPhases = NamedCompilerPhase(
             delegateToPrimaryConstructorLoweringPhase then
             // Common prefix ends
 
+            jsInteropFunctionsLowering then
+            jsInteropFunctionCallsLowering then
+
             enumEntryInstancesLoweringPhase then
             enumEntryInstancesBodyLoweringPhase then
             enumClassCreateInitializerLoweringPhase then
@@ -536,7 +556,7 @@ val wasmPhases = NamedCompilerPhase(
 
             forLoopsLoweringPhase then
             propertyAccessorInlinerLoweringPhase then
-            stringConstructorLowering then
+            stringConcatenationLowering then
 
             defaultArgumentStubGeneratorPhase then
             defaultArgumentPatchOverridesPhase then
@@ -564,6 +584,7 @@ val wasmPhases = NamedCompilerPhase(
             builtInsLoweringPhase0 then
 
             autoboxingTransformerPhase then
+            explicitlyCastExternalTypesPhase then
             objectUsageLoweringPhase then
             typeOperatorLoweringPhase then
 

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmSymbols.kt

@@ -23,6 +23,7 @@ import org.jetbrains.kotlin.ir.types.classifierOrFail
 import org.jetbrains.kotlin.ir.types.defaultType
 import org.jetbrains.kotlin.ir.types.typeWith
 import org.jetbrains.kotlin.ir.util.SymbolTable
+import org.jetbrains.kotlin.ir.util.constructors
 import org.jetbrains.kotlin.ir.util.render
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
@@ -157,9 +158,7 @@ class WasmSymbols(
     val nullableFloatIeee754Equals = getInternalFunction("nullableFloatIeee754Equals")
     val nullableDoubleIeee754Equals = getInternalFunction("nullableDoubleIeee754Equals")
 
-    val exportString = getInternalFunction("exportString")
     val unsafeGetScratchRawMemory = getInternalFunction("unsafeGetScratchRawMemory")
-
     val startCoroutineUninterceptedOrReturnIntrinsics =
         (0..2).map { getInternalFunction("startCoroutineUninterceptedOrReturnIntrinsic$it") }
 
@@ -206,6 +205,29 @@ class WasmSymbols(
         }
     }
 
+    private val wasmDataRefClass = getIrClass(FqName("kotlin.wasm.internal.reftypes.dataref"))
+    val wasmDataRefType by lazy { wasmDataRefClass.defaultType }
+
+
+    inner class JsInteropAdapters {
+        val kotlinToJsStringAdapter = getInternalFunction("kotlinToJsStringAdapter")
+        val kotlinToJsBooleanAdapter = getInternalFunction("kotlinToJsBooleanAdapter")
+        val kotlinToJsAnyAdapter = getInternalFunction("kotlinToJsAnyAdapter")
+        val jsToKotlinAnyAdapter = getInternalFunction("jsToKotlinAnyAdapter")
+        val jsToKotlinStringAdapter = getInternalFunction("jsToKotlinStringAdapter")
+        val jsToKotlinByteAdapter = getInternalFunction("jsToKotlinByteAdapter")
+        val jsToKotlinShortAdapter = getInternalFunction("jsToKotlinShortAdapter")
+        val jsToKotlinCharAdapter = getInternalFunction("jsToKotlinCharAdapter")
+    }
+
+    val jsInteropAdapters = JsInteropAdapters()
+
+    private val jsExportClass = getIrClass(FqName("kotlin.js.JsExport"))
+    val jsExportConstructor by lazy { jsExportClass.constructors.single() }
+
+    private val jsNameClass = getIrClass(FqName("kotlin.js.JsName"))
+    val jsNameConstructor by lazy { jsNameClass.constructors.single() }
+
     private fun findClass(memberScope: MemberScope, name: Name): ClassDescriptor =
         memberScope.getContributedClassifier(name, NoLookupLocation.FROM_BACKEND) as ClassDescriptor
 

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

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.backend.common.phaser.PhaseConfig
 import org.jetbrains.kotlin.backend.common.phaser.invokeToplevel
 import org.jetbrains.kotlin.backend.wasm.ir2wasm.WasmCompiledModuleFragment
 import org.jetbrains.kotlin.backend.wasm.ir2wasm.WasmModuleFragmentGenerator
+import org.jetbrains.kotlin.backend.wasm.lower.markExportedDeclarations
 import org.jetbrains.kotlin.ir.backend.js.MainModule
 import org.jetbrains.kotlin.ir.backend.js.ModulesStructure
 import org.jetbrains.kotlin.ir.backend.js.loadIr
@@ -45,7 +46,7 @@ fun compileWasm(
     }
 
     val moduleDescriptor = moduleFragment.descriptor
-    val context = WasmBackendContext(moduleDescriptor, irBuiltIns, symbolTable, moduleFragment, exportedDeclarations, configuration)
+    val context = WasmBackendContext(moduleDescriptor, irBuiltIns, symbolTable, moduleFragment, configuration)
 
     // Load declarations referenced during `context` initialization
     allModules.forEach {
@@ -63,6 +64,8 @@ fun compileWasm(
     deserializer.postProcess()
     symbolTable.noUnboundLeft("Unbound symbols at the end of linker")
 
+    moduleFragment.files.forEach { irFile -> markExportedDeclarations(context, irFile, exportedDeclarations) }
+
     wasmPhases.invokeToplevel(phaseConfig, context, moduleFragment)
 
     val compiledWasmModule = WasmCompiledModuleFragment(context.irBuiltIns)
@@ -89,9 +92,12 @@ fun compileWasm(
 
 
 fun WasmCompiledModuleFragment.generateJs(): String {
+    //language=js
     val runtime = """
     var wasmInstance = null;
     
+    const externrefBoxes = new WeakMap();
+    
     const runtime = {
         identity(x) {
             return x;

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/BodyGenerator.kt

@@ -185,18 +185,6 @@ class BodyGenerator(val context: WasmFunctionCodegenContext) : IrElementVisitorV
             else
                 context.referenceLocal(valueSymbol)
         )
-
-        if (valueSymbol.owner is IrValueParameter) {
-            val parent = valueDeclaration.parent
-            if (parent is IrFunction && parent.isExported(backendContext)) {
-                val type = context.transformType(valueDeclaration.type)
-                if (type is WasmRefNullType) {
-                    // TODO: Add these casts as IR-2-IR lowering instead
-                    generateTypeRTT(valueDeclaration.type)
-                    body.buildRefCast()
-                }
-            }
-        }
     }
 
     override fun visitSetValue(expression: IrSetValue) {
@@ -324,16 +312,6 @@ class BodyGenerator(val context: WasmFunctionCodegenContext) : IrElementVisitorV
             body.buildCall(context.referenceFunction(function.symbol))
         }
 
-        // Return types of imported functions cannot have concrete struct/array references.
-        // Non-primitive return types are represented as eqref which need to be casted back to expected type on call site.
-        if (function.getWasmImportAnnotation() != null || function.getJsFunAnnotation() != null || function.isExternal || function.isExported(backendContext)) {
-            val resT = context.transformResultType(function.returnType)
-            if (resT is WasmRefNullType) {
-                generateTypeRTT(function.returnType)
-                body.buildRefCast()
-            }
-        }
-
         // Unit types don't cross function boundaries
         if (function.returnType == irBuiltIns.unitType)
             body.buildGetUnit()
@@ -460,14 +438,6 @@ class BodyGenerator(val context: WasmFunctionCodegenContext) : IrElementVisitorV
             body.buildGetLocal(context.referenceLocal(0))
         }
 
-        // Handle complex exported parameters.
-        // TODO: This should live as a separate lowering which creates separate shims for each exported function.
-        if (context.irFunction.isExported(context.backendContext) &&
-            expression.value.type.getClass() == irBuiltIns.stringType.getClass()) {
-
-            body.buildCall(context.referenceFunction(wasmSymbols.exportString))
-        }
-
         body.buildInstr(WasmOp.RETURN)
     }
 

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/DeclarationGenerator.kt

@@ -14,6 +14,7 @@ import org.jetbrains.kotlin.ir.IrBuiltIns
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.backend.js.utils.isJsExport
 import org.jetbrains.kotlin.ir.backend.js.utils.findUnitGetInstanceFunction
+import org.jetbrains.kotlin.ir.backend.js.utils.getJsNameOrKotlinName
 import org.jetbrains.kotlin.ir.backend.js.utils.realOverrideTarget
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.IrBlockBody
@@ -69,33 +70,18 @@ class DeclarationGenerator(val context: WasmModuleCodegenContext) : IrElementVis
         // Generate function type
         val watName = declaration.fqNameWhenAvailable.toString()
         val irParameters = declaration.getEffectiveValueParameters()
-        // TODO: Exported types should be transformed in a separate lowering by creating shim functions for each export.
-        val isExported = declaration.isExported(context.backendContext)
         val resultType =
             when {
-                isExported -> context.transformExportedResultType(declaration.returnType)
                 // Unit_getInstance returns true Unit reference instead of "void"
                 declaration == unitGetInstanceFunction -> context.transformType(declaration.returnType)
                 else -> context.transformResultType(declaration.returnType)
             }
 
-        val isExportedOrImported = isExported || importedName != null
         val wasmFunctionType =
             WasmFunctionType(
                 name = watName,
-                parameterTypes = irParameters.map {
+                parameterTypes = irParameters.map { context.transformValueParameterType(it) },
-                    val t = context.transformValueParameterType(it)
+                resultTypes = listOfNotNull(resultType)
-                    if (isExportedOrImported && t is WasmRefNullType) {
-                        WasmRefNullType(WasmHeapType.Simple.Data)
-                    } else {
-                        t
-                    }
-                },
-                resultTypes = listOfNotNull(
-                    resultType.let {
-                        if (isExportedOrImported && it is WasmRefNullType) WasmRefNullType(WasmHeapType.Simple.Data) else it
-                    }
-                )
             )
         context.defineFunctionType(declaration.symbol, wasmFunctionType)
 
@@ -164,12 +150,11 @@ class DeclarationGenerator(val context: WasmModuleCodegenContext) : IrElementVis
         if (initPriority != null)
             context.registerInitFunction(function, initPriority)
 
-        if (declaration.isExported(backendContext)) {
+        if (declaration.isExported()) {
             context.addExport(
                 WasmExport.Function(
                     field = function,
-                    // TODO: Add ability to specify exported name.
+                    name = declaration.getJsNameOrKotlinName().identifier
-                    name = declaration.name.identifier
                 )
             )
         }
@@ -371,7 +356,7 @@ fun generateDefaultInitializerForType(type: WasmType, g: WasmExpressionBuilder)
     WasmF32 -> g.buildConstF32(0f)
     WasmF64 -> g.buildConstF64(0.0)
     is WasmRefNullType -> g.buildRefNull(type.heapType)
-    is WasmExternRef -> g.buildRefNull(WasmHeapType.Simple.Extern)
+    is WasmExternRef, is WasmAnyRef -> g.buildRefNull(WasmHeapType.Simple.Extern)
     WasmUnreachableType -> error("Unreachable type can't be initialized")
     else -> error("Unknown value type ${type.name}")
 }
@@ -381,5 +366,5 @@ fun IrFunction.getEffectiveValueParameters(): List<IrValueParameter> {
     return listOfNotNull(implicitThis, dispatchReceiverParameter, extensionReceiverParameter) + valueParameters
 }
 
-fun IrFunction.isExported(context: WasmBackendContext): Boolean =
+fun IrFunction.isExported(): Boolean =
-    fqNameWhenAvailable in context.additionalExportedDeclarations || isJsExport()
+    isJsExport()

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/TypeTransformer.kt

@@ -12,9 +12,12 @@ import org.jetbrains.kotlin.ir.declarations.IrTypeParameter
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.symbols.IrTypeParameterSymbol
 import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.classOrNull
 import org.jetbrains.kotlin.ir.types.classifierOrNull
 import org.jetbrains.kotlin.ir.types.getClass
 import org.jetbrains.kotlin.ir.util.isInterface
+import org.jetbrains.kotlin.ir.util.packageFqName
+import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.wasm.ir.*
 
 class WasmTypeTransformer(
@@ -93,13 +96,21 @@ class WasmTypeTransformer(
             symbols.voidType ->
                 error("Void type can't be used as a value")
 
-            // this also handles builtIns.stringType
             else -> {
                 val klass = this.getClass()
                 val ic = context.backendContext.inlineClassesUtils.getInlinedClass(this)
 
                 if (klass != null && (klass.hasWasmForeignAnnotation() || klass.isExternal)) {
-                    WasmExternRef
+                    WasmAnyRef
+                } else if (klass != null && isBuiltInWasmRefType(this)) {
+                    when (val name = klass.name.identifier) {
+                        "anyref" -> WasmAnyRef
+                        "eqref" -> WasmEqRef
+                        "dataref" -> WasmRefNullType(WasmHeapType.Simple.Data)
+                        "i31ref" -> WasmI31Ref
+                        "funcref" -> WasmRefNullType(WasmHeapType.Simple.Func)
+                        else -> error("Unknown reference type $name")
+                    }
                 } else if (ic != null) {
                     context.backendContext.inlineClassesUtils.getInlineClassUnderlyingType(ic).toWasmValueType()
                 } else {
@@ -109,6 +120,12 @@ class WasmTypeTransformer(
         }
 }
 
+fun isBuiltInWasmRefType(type: IrType): Boolean {
+    return type.classOrNull?.owner?.packageFqName == FqName("kotlin.wasm.internal.reftypes")
+}
+
+fun isExternalType(type: IrType): Boolean =
+    type.erasedUpperBound?.isExternal ?: false
 
 // Return null if upper bound is Any
 private val IrTypeParameter.erasedUpperBound: IrClass?

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/WasmBaseCodegenContext.kt

@@ -43,7 +43,6 @@ interface WasmBaseCodegenContext {
     fun transformBoxedType(irType: IrType): WasmType
     fun transformValueParameterType(irValueParameter: IrValueParameter): WasmType
     fun transformResultType(irType: IrType): WasmType?
-    fun transformExportedResultType(irType: IrType): WasmType?
     fun transformBlockResultType(irType: IrType): WasmType?
 
 

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/WasmModuleCodegenContextImpl.kt

@@ -58,13 +58,6 @@ class WasmModuleCodegenContextImpl(
         return with(typeTransformer) { irType.toWasmResultType() }
     }
 
-    override fun transformExportedResultType(irType: IrType): WasmType? {
-        // Exported strings are passed as pointers to the raw memory
-        if (irType.getClass() == backendContext.irBuiltIns.stringType.getClass())
-            return WasmI32
-        return with(typeTransformer) { irType.toWasmResultType() }
-    }
-
     override fun transformBlockResultType(irType: IrType): WasmType? {
         return with(typeTransformer) { irType.toWasmBlockResultType() }
     }

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

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.backend.wasm.lower
+
+import org.jetbrains.kotlin.backend.wasm.WasmBackendContext
+import org.jetbrains.kotlin.backend.wasm.ir2wasm.isExternalType
+import org.jetbrains.kotlin.ir.backend.js.ir.JsIrBuilder
+import org.jetbrains.kotlin.ir.backend.js.lower.AbstractValueUsageLowering
+import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.types.IrType
+
+/**
+ * Insert casts between external and non-external types
+ */
+class ExplicitlyCastExternalTypesLowering(wasmContext: WasmBackendContext) : AbstractValueUsageLowering(wasmContext) {
+    override fun IrExpression.useExpressionAsType(actualType: IrType, expectedType: IrType): IrExpression {
+        val expectedExternal = isExternalType(expectedType)
+        val actualExternal = isExternalType(actualType)
+
+        if (expectedExternal != actualExternal) {
+            return JsIrBuilder.buildImplicitCast(this, toType = expectedType)
+        }
+
+        return this
+    }
+}

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

@@ -0,0 +1,308 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.backend.wasm.lower
+
+import org.jetbrains.kotlin.backend.common.BodyLoweringPass
+import org.jetbrains.kotlin.backend.common.DeclarationTransformer
+import org.jetbrains.kotlin.backend.common.ir.createStaticFunctionWithReceivers
+import org.jetbrains.kotlin.backend.common.lower.DeclarationIrBuilder
+import org.jetbrains.kotlin.backend.common.lower.createIrBuilder
+import org.jetbrains.kotlin.backend.wasm.WasmBackendContext
+import org.jetbrains.kotlin.backend.wasm.ir2wasm.isBuiltInWasmRefType
+import org.jetbrains.kotlin.backend.wasm.ir2wasm.isExported
+import org.jetbrains.kotlin.backend.wasm.ir2wasm.isExternalType
+import org.jetbrains.kotlin.ir.backend.js.utils.getJsNameOrKotlinName
+import org.jetbrains.kotlin.ir.builders.*
+import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrDeclaration
+import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
+import org.jetbrains.kotlin.ir.expressions.IrBody
+import org.jetbrains.kotlin.ir.expressions.IrCall
+import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.makeNullable
+import org.jetbrains.kotlin.ir.util.*
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
+import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
+import org.jetbrains.kotlin.name.Name
+
+/**
+ * Create wrappers for external and @JsExport functions when type adaptation is needed
+ */
+class JsInteropFunctionsLowering(val context: WasmBackendContext) : DeclarationTransformer {
+    val builtIns = context.irBuiltIns
+    val symbols = context.wasmSymbols
+    val adapters = symbols.jsInteropAdapters
+
+    override fun transformFlat(declaration: IrDeclaration): List<IrDeclaration>? {
+        if (declaration.isFakeOverride) return null
+        if (declaration !is IrSimpleFunction) return null
+        val isExported = declaration.isExported()
+        val isExternal = declaration.isExternal
+        if (!isExported && !isExternal) return null
+        check(!(isExported && isExternal)) { "Exported external declarations are not supported: ${declaration.fqNameWhenAvailable}" }
+        check(declaration.parent !is IrClass) { "Interop members are not supported:  ${declaration.fqNameWhenAvailable}" }
+
+        return if (isExternal)
+            transformExternalFunction(declaration)
+        else
+            transformExportFunction(declaration)
+    }
+
+    /**
+     *  external fun foo(x: KotlinType): KotlinType
+     *
+     *  ->
+     *
+     *  external fun foo(x: JsType): JsType
+     *  fun foo__externalAdapter(x: KotlinType): KotlinType = adaptResult(foo(adaptParameter(x)));
+     */
+    fun transformExternalFunction(function: IrSimpleFunction): List<IrDeclaration>? {
+        val valueParametersAdapters = function.valueParameters.map {
+            it.type.kotlinToJsAdapterIfNeeded(isReturn = false)
+        }
+        val resultAdapter =
+            function.returnType.jsToKotlinAdapterIfNeeded(isReturn = true)
+
+        if (resultAdapter == null && valueParametersAdapters.all { it == null })
+            return null
+
+        val newFun = context.irFactory.createStaticFunctionWithReceivers(
+            function.parent,
+            name = Name.identifier(function.name.asStringStripSpecialMarkers() + "__externalAdapter"),
+            function
+        )
+
+        function.valueParameters.forEachIndexed { index, newParameter ->
+            val adapter = valueParametersAdapters[index]
+            if (adapter != null) {
+                newParameter.type = adapter.toType
+            }
+        }
+        resultAdapter?.let {
+            function.returnType = resultAdapter.fromType
+        }
+
+        val builder = context.createIrBuilder(newFun.symbol)
+        newFun.body = createAdapterFunctionBody(builder, newFun, function, valueParametersAdapters, resultAdapter)
+        newFun.annotations = emptyList()
+
+        context.mapping.wasmJsInteropFunctionToWrapper[function] = newFun
+        return listOf(function, newFun)
+    }
+
+    /**
+     *  @JsExport
+     *  fun foo(x: KotlinType): KotlinType { <original-body> }
+     *
+     *  ->
+     *
+     *  @JsExport
+     *  @JsName("foo")
+     *  fun foo__JsExportAdapter(x: JsType): JsType =
+     *      adaptResult(foo(adaptParameter(x)));
+     *
+     *  fun foo(x: KotlinType): KotlinType { <original-body> }
+     */
+    fun transformExportFunction(function: IrSimpleFunction): List<IrDeclaration>? {
+        val valueParametersAdapters = function.valueParameters.map {
+            it.type.jsToKotlinAdapterIfNeeded(isReturn = false)
+        }
+        val resultAdapter =
+            function.returnType.kotlinToJsAdapterIfNeeded(isReturn = true)
+
+        if (resultAdapter == null && valueParametersAdapters.all { it == null })
+            return null
+
+        val newFun = context.irFactory.createStaticFunctionWithReceivers(
+            function.parent,
+            name = Name.identifier(function.name.asStringStripSpecialMarkers() + "__JsExportAdapter"),
+            function
+        )
+
+        newFun.valueParameters.forEachIndexed { index, newParameter ->
+            val adapter = valueParametersAdapters[index]
+            if (adapter != null) {
+                newParameter.type = adapter.fromType
+            }
+        }
+        resultAdapter?.let {
+            newFun.returnType = resultAdapter.toType
+        }
+
+        // Delegate new function to old function:
+        val builder: DeclarationIrBuilder = context.createIrBuilder(newFun.symbol)
+        newFun.body = createAdapterFunctionBody(builder, newFun, function, valueParametersAdapters, resultAdapter)
+
+        newFun.annotations += builder.irCallConstructor(context.wasmSymbols.jsNameConstructor, typeArguments = emptyList()).also {
+            it.putValueArgument(0, builder.irString(function.getJsNameOrKotlinName().identifier))
+        }
+        function.annotations = function.annotations.filter { it.symbol != context.wasmSymbols.jsExportConstructor }
+
+        return listOf(function, newFun)
+    }
+
+    private fun createAdapterFunctionBody(
+        builder: DeclarationIrBuilder,
+        function: IrSimpleFunction,
+        functionToCall: IrSimpleFunction,
+        valueParametersAdapters: List<InteropTypeAdapter?>,
+        resultAdapter: InteropTypeAdapter?
+    ) = builder.irBlockBody {
+        +irReturn(
+            irCall(functionToCall).let { call ->
+                for ((index, valueParameter) in function.valueParameters.withIndex()) {
+                    val get = irGet(valueParameter)
+                    call.putValueArgument(index, valueParametersAdapters[index]?.adapt(get, builder) ?: get)
+                }
+                resultAdapter?.adapt(call, builder) ?: call
+            }
+        )
+    }
+
+    private fun IrType.kotlinToJsAdapterIfNeeded(isReturn: Boolean): InteropTypeAdapter? {
+        if (isReturn && this == builtIns.unitType)
+            return null
+
+        when (this) {
+            builtIns.stringType -> return FunctionBasedAdapter(adapters.kotlinToJsStringAdapter.owner)
+            builtIns.stringType.makeNullable() -> return NullOrAdapter(FunctionBasedAdapter(adapters.kotlinToJsStringAdapter.owner))
+            builtIns.booleanType -> return FunctionBasedAdapter(adapters.kotlinToJsBooleanAdapter.owner)
+            builtIns.anyType -> return FunctionBasedAdapter(adapters.kotlinToJsAnyAdapter.owner)
+
+            builtIns.byteType,
+            builtIns.shortType,
+            builtIns.charType,
+            builtIns.intType,
+            builtIns.longType,
+            builtIns.floatType,
+            builtIns.doubleType,
+            context.wasmSymbols.voidType ->
+                return null
+
+        }
+
+        if (isExternalType(this))
+            return null
+
+        if (isBuiltInWasmRefType(this))
+            return null
+
+        return SendKotlinObjectToJsAdapter(this)
+    }
+
+    private fun IrType.jsToKotlinAdapterIfNeeded(isReturn: Boolean): InteropTypeAdapter? {
+        if (isReturn && this == builtIns.unitType)
+            return null
+
+        when (this) {
+            builtIns.stringType -> return FunctionBasedAdapter(adapters.jsToKotlinStringAdapter.owner)
+            builtIns.anyType -> return FunctionBasedAdapter(adapters.jsToKotlinAnyAdapter.owner)
+            builtIns.byteType -> return FunctionBasedAdapter(adapters.jsToKotlinByteAdapter.owner)
+            builtIns.shortType -> return FunctionBasedAdapter(adapters.jsToKotlinShortAdapter.owner)
+            builtIns.charType -> return FunctionBasedAdapter(adapters.jsToKotlinCharAdapter.owner)
+
+            builtIns.booleanType,
+            builtIns.intType,
+            builtIns.longType,
+            builtIns.floatType,
+            builtIns.doubleType,
+            context.wasmSymbols.voidType ->
+                return null
+        }
+
+        if (isExternalType(this))
+            return null
+
+        if (isBuiltInWasmRefType(this))
+            return null
+
+        return ReceivingKotlinObjectFromJsAdapter(this)
+    }
+
+    interface InteropTypeAdapter {
+        val fromType: IrType
+        val toType: IrType
+        fun adapt(expression: IrExpression, builder: IrBuilderWithScope): IrExpression
+    }
+
+    /**
+     * Adapter implemented as a single function call
+     */
+    class FunctionBasedAdapter(
+        private val function: IrSimpleFunction,
+    ) : InteropTypeAdapter {
+        override val fromType = function.valueParameters[0].type
+        override val toType = function.returnType
+        override fun adapt(expression: IrExpression, builder: IrBuilderWithScope): IrExpression {
+            val call = builder.irCall(function)
+            call.putValueArgument(0, expression)
+            return call
+        }
+    }
+
+    /**
+     * Current V8 Wasm GC mandates dataref type instead of structs and arrays
+     */
+    inner class SendKotlinObjectToJsAdapter(
+        override val fromType: IrType
+    ) : InteropTypeAdapter {
+        override val toType: IrType = context.wasmSymbols.wasmDataRefType
+        override fun adapt(expression: IrExpression, builder: IrBuilderWithScope): IrExpression {
+            return builder.irReinterpretCast(expression, toType)
+        }
+    }
+
+    /**
+     * Current V8 Wasm GC mandates dataref type instead of structs and arrays
+     */
+    inner class ReceivingKotlinObjectFromJsAdapter(
+        override val toType: IrType
+    ) : InteropTypeAdapter {
+        override val fromType: IrType = context.wasmSymbols.wasmDataRefType
+        override fun adapt(expression: IrExpression, builder: IrBuilderWithScope): IrExpression {
+            val call = builder.irCall(context.wasmSymbols.wasmRefCast)
+            call.putValueArgument(0, expression)
+            call.putTypeArgument(0, toType)
+            return call
+        }
+    }
+
+    /**
+     * Effectively `value?.let { adapter(it) }`
+     */
+    inner class NullOrAdapter(
+        val adapter: InteropTypeAdapter
+    ) : InteropTypeAdapter {
+        override val fromType: IrType = adapter.fromType.makeNullable()
+        override val toType: IrType = adapter.toType.makeNullable()
+        override fun adapt(expression: IrExpression, builder: IrBuilderWithScope): IrExpression {
+            return builder.irComposite {
+                val tmp = irTemporary(adapter.adapt(expression, builder))
+                +irIfNull(toType, irGet(tmp), irNull(toType), irImplicitCast(irGet(tmp), toType))
+            }
+        }
+    }
+}
+
+/**
+ * Redirect calls to external and @JsExport functions to created wrappers
+ */
+class JsInteropFunctionCallsLowering(val context: WasmBackendContext) : BodyLoweringPass {
+    override fun lower(irBody: IrBody, container: IrDeclaration) {
+        irBody.transformChildrenVoid(object : IrElementTransformerVoid() {
+            override fun visitCall(expression: IrCall): IrExpression {
+                expression.transformChildrenVoid()
+                val newFun: IrSimpleFunction? = context.mapping.wasmJsInteropFunctionToWrapper[expression.symbol.owner]
+                return if (newFun != null && container != newFun) {
+                    irCall(expression, newFun)
+                } else {
+                    expression
+                }
+            }
+        })
+    }
+}

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

@@ -152,6 +152,8 @@ class WasmBaseTypeOperatorTransformer(val context: WasmBackendContext) : IrEleme
     private fun generateTypeCheckNonNull(argument: IrExpression, toType: IrType): IrExpression {
         assert(!toType.isMarkedNullable())
         return when {
+            // TODO: Use instanceof for classes later
+            toType.eraseToClassOrInterface.isExternal -> builder.irTrue()
             toType.isNothing() -> builder.irFalse()
             toType.isTypeParameter() -> generateTypeCheckWithTypeParameter(argument, toType)
             toType.isInterface() -> generateIsInterface(argument, toType)
@@ -190,7 +192,28 @@ class WasmBaseTypeOperatorTransformer(val context: WasmBackendContext) : IrEleme
             }
         }
 
-        if (fromType.eraseToClassOrInterface.isSubclassOf(toType.eraseToClassOrInterface)) {
+        val fromClass = fromType.eraseToClassOrInterface
+        val toClass = toType.eraseToClassOrInterface
+
+        if (fromClass.isExternal && toClass.isExternal) {
+            return value
+        }
+
+        if (fromClass.isExternal && !toClass.isExternal) {
+            val narrowingToAny = builder.irCall(symbols.jsInteropAdapters.jsToKotlinAnyAdapter).also {
+                it.putValueArgument(0, value)
+            }
+            // Continue narrowing from Any to expected type
+            return narrowType(context.irBuiltIns.anyType, toType, narrowingToAny)
+        }
+
+        if (toClass.isExternal && !fromClass.isExternal) {
+            return builder.irCall(symbols.jsInteropAdapters.kotlinToJsAnyAdapter).also {
+                it.putValueArgument(0, value)
+            }
+        }
+
+        if (fromClass.isSubclassOf(toClass)) {
             return value
         }
         if (toType.isNothing()) {

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

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.backend.wasm.lower
+
+import org.jetbrains.kotlin.backend.common.lower.createIrBuilder
+import org.jetbrains.kotlin.backend.wasm.WasmBackendContext
+import org.jetbrains.kotlin.ir.builders.irCallConstructor
+import org.jetbrains.kotlin.ir.declarations.IrFile
+import org.jetbrains.kotlin.ir.declarations.IrFunction
+import org.jetbrains.kotlin.ir.util.fqNameWhenAvailable
+import org.jetbrains.kotlin.name.FqName
+
+/**
+ * Mark declarations from [exportedFqNames] with @JsExport annotation
+ */
+fun markExportedDeclarations(context: WasmBackendContext, irFile: IrFile, exportedFqNames: Set<FqName>) {
+    for (declaration in irFile.declarations) {
+        if (declaration is IrFunction && declaration.fqNameWhenAvailable in exportedFqNames) {
+            val builder = context.createIrBuilder(irFile.symbol)
+            declaration.annotations +=
+                builder.irCallConstructor(context.wasmSymbols.jsExportConstructor, typeArguments = emptyList())
+        }
+    }
+}

compiler/ir/serialization.js/src/org/jetbrains/kotlin/ir/backend/js/JsMapping.kt

@@ -40,6 +40,10 @@ class JsMapping(val state: JsMappingState) : DefaultMapping(state) {
         state.newDeclarationToDeclarationMapping<IrSimpleFunction, IrSimpleFunction>()
 
     val suspendArityStore = state.newDeclarationToDeclarationCollectionMapping<IrClass, Collection<IrSimpleFunction>>()
+
+    // Wasm mappings
+    val wasmJsInteropFunctionToWrapper =
+        state.newDeclarationToDeclarationMapping<IrSimpleFunction, IrSimpleFunction>()
 }
 
 

compiler/testData/codegen/boxWasmJsInterop/externalTypeOperators.kt

@@ -0,0 +1,231 @@
+// WITH_RUNTIME
+// FILE: externals.js
+
+const primitives1 = [3.14, "Test string 1",  true, Symbol("symbol"), 131283889534859707199254740992n];
+const primitives2 = [3.15, "Test string 2", false, Symbol("symbol"), 231283889534859707199254740992n];
+
+function getPrimitive1(n) {
+    return primitives1[n];
+}
+
+function getPrimitive2(n) {
+    return primitives2[n];
+}
+
+function testPrimitive(obj, n) {
+    return obj === primitives1[n];
+}
+
+function getNewObject() {
+    return { value: 123 };
+}
+
+function testObject(obj) {
+    return obj.value === 123;
+}
+
+function getNewArray() {
+    return [1, 2, 3];
+}
+
+function testArray(obj) {
+    return Array.isArray(obj) && obj[0] === 1 && obj[1] === 2 && obj [2] === 3;
+}
+
+function roundTrip(x) { return x; }
+
+// FILE: externals.kt
+external interface Obj
+external interface SubObj : Obj
+
+external fun getPrimitive1(n: Int): Obj
+external fun getPrimitive2(n: Int): Obj
+external fun testPrimitive(obj: Obj, n: Int): Boolean
+
+external fun getNewObject(): Obj
+external fun testObject(obj: Obj): Boolean
+
+external fun getNewArray(): Obj
+external fun testArray(obj: Obj): Boolean
+
+external fun roundTrip(x: Obj): Obj
+
+fun assertTrue(x: Boolean) {
+    if (!x) error("assertTrue fail")
+}
+
+fun assertFalse(x: Boolean) {
+    if (x) error("assertFalse fail")
+}
+
+fun multiCast(obj: Obj): Obj =
+    obj
+            as Any as Any
+            as Any as? Any
+            as Any as Any?
+            as Any as? Any?
+            as Any as Obj
+            as Any as? Obj
+            as Any as Obj?
+            as Any as? Obj?
+
+            as Any? as Any
+            as Any? as? Any
+            as Any? as Any?
+            as Any? as? Any?
+            as Any? as Obj
+            as Any? as? Obj
+            as Any? as Obj?
+            as Any? as? Obj?
+
+            as Obj as Any
+            as Obj as? Any
+            as Obj as Any?
+            as Obj as? Any?
+            as Obj as Obj
+            as Obj as? Obj
+            as Obj as Obj?
+            as Obj as? Obj?
+
+            as Obj? as Any
+            as Obj? as? Any
+            as Obj? as Any?
+            as Obj? as? Any?
+            as Obj? as Obj
+            as Obj? as? Obj
+            as Obj? as Obj?
+            as Obj? as? Obj?
+            as Obj
+
+class CustomClass
+interface CustomInterface
+
+fun <T1 : Any, T2 : Any?, T3 : Obj> testWithTypeParameters(obj: Obj, checkObj: (Any?) -> Unit) {
+    checkObj(obj as T1)
+    checkObj(obj as T2)
+    checkObj(obj as T3)
+    checkObj(obj as? T1)
+    checkObj(obj as? T2)
+    checkObj(obj as? T3)
+    checkObj(obj as T1?)
+    checkObj(obj as T2?)
+    checkObj(obj as T3?)
+    checkObj(obj as? T1?)
+    checkObj(obj as? T2?)
+    checkObj(obj as? T3?)
+}
+
+fun test(
+    obj: Obj,
+    anotherObj: Obj,
+    checkObj: (Any?) -> Unit,
+    stableIdentity: Boolean
+) {
+    checkObj(obj)
+    checkObj(obj as Any)
+    checkObj(obj as? Any)
+    checkObj(obj as Any?)
+    checkObj(obj as? Any?)
+    testWithTypeParameters<Any, Any?, Obj>(obj, checkObj)
+    val subObj: SubObj = obj as SubObj
+    checkObj(subObj)
+    checkObj(subObj as Obj)
+    val roundTrippedObj = roundTrip(obj)
+    checkObj(roundTrippedObj)
+    assertTrue(obj == roundTrippedObj)
+    if (stableIdentity)
+        assertTrue(obj === roundTrippedObj)
+
+    val castedObj = multiCast(roundTrippedObj)
+    checkObj(castedObj)
+
+    assertTrue(obj is Any)
+    assertTrue(obj is Any?)
+    assertFalse(obj !is Any)
+    assertFalse(obj !is Any?)
+
+    assertFalse(obj as Any is CustomClass)
+    assertFalse(obj as Any is CustomInterface)
+
+    val objects = listOf<Obj>(obj, roundTrippedObj, castedObj)
+    for (obj1 in objects) {
+        checkObj(obj1)
+        assertTrue(obj1.hashCode() == obj.hashCode())
+        assertTrue(obj1.toString() == obj.toString())
+        assertTrue(obj != anotherObj)
+        assertTrue(obj !== anotherObj)
+        for (obj2 in objects) {
+            assertTrue(obj1 == obj2)
+            if (stableIdentity)
+                assertTrue(obj1 === obj2)
+            assertTrue(obj1.hashCode() == obj2.hashCode())
+            assertTrue(obj1.toString() == obj2.toString())
+        }
+    }
+    assertTrue(objects.size == 3)
+    assertTrue(objects.toSet().size == 1)
+    assertTrue((objects + anotherObj).toSet().size == 2)
+}
+
+fun testPrimitive(n: Int) {
+    test(
+        getPrimitive1(n),
+        getPrimitive2(n),
+        { obj ->
+            if (!testPrimitive(obj as Obj, n)) {
+                error("Fail $n")
+            }
+        },
+        stableIdentity = false,
+    )
+}
+
+class C(val x: Int)
+value class IC(val x: Int)
+
+fun box(): String {
+    for (i in 0..2) { // TODO: Symbols and BigInts are not supprted in Wasm
+        testPrimitive(i)
+    }
+
+    test(
+        getNewObject(),
+        getNewObject(),
+        { obj ->
+            if (!testObject(obj as Obj)) {
+                error("Fail object")
+            }
+        },
+        stableIdentity = true,
+    )
+
+    test(
+        getNewArray(),
+        getNewArray(),
+        { obj ->
+            if (!testArray(obj as Obj)) {
+                error("Fail object")
+            }
+        },
+        stableIdentity = true,
+    )
+
+
+    val kotlinValues = listOf(10, "10", true,  arrayOf(10), intArrayOf(20), C(10), IC(10))
+    val otherValues  = listOf(11, "11", false, arrayOf(12), intArrayOf(22), C(11), IC(11))
+
+    for ((value, otherValue) in kotlinValues.zip(otherValues)) {
+        test(
+            value as Obj,
+            otherValues as Obj,
+            { obj ->
+                if (obj !== value) {
+                    error("Fail custom class")
+                }
+            },
+            stableIdentity = true,
+        )
+    }
+
+    return "OK"
+}

compiler/testData/codegen/boxWasmJsInterop/jsExport.kt

@@ -9,6 +9,20 @@ fun makeC(x: Int): C = C(x)
 @JsExport
 fun getX(c: C): Int = c.x
 
+@JsExport
+fun getString(s: String): String = "Test string $s";
+
+@JsExport
+fun isEven(x: Int): Boolean = x % 2 == 0
+
+external interface EI
+
+@JsExport
+fun eiAsAny(ei: EI): Any = ei
+
+@JsExport
+fun anyAsEI(any: Any): EI = any as EI
+
 fun box(): String = "OK"
 
 // FILE: jsExport__after.js
@@ -16,4 +30,16 @@ fun box(): String = "OK"
 const c = main.makeC(300);
 if (main.getX(c) !== 300) {
     throw "Fail 1";
+}
+
+if (main.getString("2") !== "Test string 2") {
+    throw "Fail 2";
+}
+
+if (main.isEven(31) !== false || main.isEven(10) !== true) {
+    throw "Fail 3";
+}
+
+if (main.anyAsEI(main.eiAsAny({x:10})).x !== 10) {
+    throw "Fail 4";
 }

compiler/testData/codegen/boxWasmJsInterop/nullableExternRefs.kt

@@ -0,0 +1,65 @@
+// TARGET_BACKEND: WASM
+// WITH_RUNTIME
+
+// FILE: externals.js
+
+function roundTrip(x) { return x; }
+
+// FILE: externals.kt
+
+external fun roundTrip(x: EI?): EI?
+
+fun assertTrue(x: Boolean) {
+    if (!x) error("assertTrue fail")
+}
+
+fun assertFalse(x: Boolean) {
+    if (x) error("assertFalse fail")
+}
+
+external interface EI
+
+@JsFun("() => null")
+external fun getNull(): EI?
+
+@JsFun("() => undefined")
+external fun getUndefined(): EI?
+
+@JsFun("(ref) => ref === null")
+external fun isJsNull(ref: EI?): Boolean
+
+@JsFun("(ref) => ref === undefined")
+external fun isJsUndefined(ref: EI?): Boolean
+
+@JsFun("() => null")
+external fun getJsNullAsNonNullable(): EI
+
+@JsFun("() => undefined")
+external fun getJsUndefinedAsNonNullable(): EI
+
+fun box(): String {
+    val jsNull = getNull()
+    val jsUndefined = getUndefined()
+
+    assertTrue(jsNull == null)
+    assertTrue((jsNull as Any?) == null)
+    assertTrue((jsNull as Any?) === null)
+    assertTrue(jsUndefined == null)
+
+    assertTrue(isJsNull(null))
+    assertTrue(isJsNull(null as EI?))
+    assertTrue(isJsNull(null as? EI?))
+    assertTrue(isJsNull(roundTrip(null)))
+    assertTrue(isJsNull(jsNull))
+
+    assertFalse(isJsUndefined(null))
+    assertTrue(isJsUndefined(jsUndefined))
+
+    // TODO: Should these fail?
+    val n2 = getJsNullAsNonNullable()
+    val ud2 = getJsUndefinedAsNonNullable()
+    assertTrue(isJsNull(n2))
+    assertTrue(isJsUndefined(ud2))
+
+    return "OK"
+}

compiler/testData/codegen/boxWasmJsInterop/types.kt

@@ -0,0 +1,112 @@
+// FILE: externals.js
+
+// -- Strings --
+
+function isTestString(x) {
+    return x === "Test string";
+}
+
+function getTestString() {
+    return "Test string";
+}
+
+function concatStrings(x, y) {
+    if (typeof x !== "string") return "Fail 1";
+    if (typeof y !== "string") return "Fail 2";
+    return x + y;
+}
+
+function concatStringsNullable(x, y) {
+    return concatStrings(x ?? "<null>", y ?? "<null>")
+}
+
+// -- Booleans --
+
+function isTrueBoolean(x) {
+    if (typeof x !== "boolean") return "Fail";
+    return x === true;
+}
+
+function isFalseBoolean(x) {
+    if (typeof x !== "boolean") return "Fail";
+    return x === false;
+}
+
+function getTrueBoolean(x) {
+    return true;
+}
+
+function getFalseBoolean(x) {
+    return false;
+}
+
+// -- Any --
+
+function createJsObjectAsAny() {
+    return { value: "object created by createJsObjectAsAny" };
+}
+
+function createJsObjectAsExternalInterface() {
+    return { value: "object created by createJsObjectAsExternalInterface" };
+}
+
+function getObjectValueEI(x) {
+    return x.value;
+}
+
+function getObjectValueAny(x) {
+    return x.value;
+}
+
+// FILE: externals.kt
+
+external fun isTestString(x: String): Boolean
+external fun getTestString(): String
+external fun concatStrings(x: String, y: String): String
+//external fun concatStringsNullable(x: String?, y: String?): String?
+
+external fun isTrueBoolean(x: Boolean): Boolean
+external fun isFalseBoolean(x: Boolean): Boolean
+external fun getTrueBoolean(): Boolean
+external fun getFalseBoolean(): Boolean
+
+external interface EI
+
+external fun createJsObjectAsAny(): Any
+external fun createJsObjectAsExternalInterface(): EI
+external fun getObjectValueEI(x: EI): String
+external fun getObjectValueAny(x: Any): String
+
+fun box(): String {
+    // Strings
+    if (!isTestString("Test string")) return "Fail !isTestString"
+    if (isTestString("Test string 2")) return "Fail isTestString"
+    if (getTestString() != "Test string") return "Fail getTestString"
+    if (concatStrings("A", "B") != "AB") return "Fail concatStrings 1"
+    if (concatStrings("Привет ", "😀\uD83D") != "Привет 😀\uD83D") return "Fail concatStrings 2"
+//    if (concatStringsNullable("A", "B") != "AB") return "Fail concatStringsNullable 1"
+
+    // Boolean
+    if (!isTrueBoolean(true)) return "Fail !isTrueBoolean"
+    if (isTrueBoolean(false)) return "Fail isTrueBoolean"
+    if (!isFalseBoolean(false)) return "Fail !isFalseBoolean"
+    if (isFalseBoolean(true)) return "Fail isFalseBoolean"
+    if (getTrueBoolean() != true) return "Fail getTrueBoolean"
+    if (getFalseBoolean() != false) return "Fail getFalseBoolean"
+
+    // External interface
+    val objAsEI: EI = createJsObjectAsExternalInterface()
+    if (getObjectValueEI(objAsEI) != "object created by createJsObjectAsExternalInterface")
+        return "Fail createJsObjectAsExternalInterface + getObjectValueEI"
+    if (getObjectValueAny(objAsEI) != "object created by createJsObjectAsExternalInterface")
+        return "Fail createJsObjectAsExternalInterface + getObjectValueAny"
+
+    // Any
+    val objAsAny: Any = createJsObjectAsAny()
+    if (getObjectValueAny(objAsAny) != "object created by createJsObjectAsAny")
+        return "Fail createJsObjectAsAny + getObjectValueAny"
+    if (getObjectValueEI(objAsAny as EI) != "object created by createJsObjectAsAny")
+        return "Fail createJsObjectAsAny + getObjectValueEI"
+
+    return "OK"
+}

js/js.tests/test/org/jetbrains/kotlin/js/test/BasicWasmBoxTest.kt

@@ -195,7 +195,7 @@ abstract class BasicWasmBoxTest(
             
             wasmInstance.exports.startUnitTests?.();
 
-            const actualResult = importStringFromWasm(wasmInstance.exports.$testFunction());
+            const actualResult = wasmInstance.exports.$testFunction();
             if (actualResult !== "OK")
                 throw `Wrong box result '${'$'}{actualResult}'; Expected "OK"`;
         """.trimIndent()

js/js.tests/test/org/jetbrains/kotlin/js/test/ir/semantics/abstractClassesForGeneratedIrTests.kt

@@ -23,3 +23,9 @@ abstract class AbstractIrJsCodegenInlineTest : BasicIrBoxTest(
     "compiler/testData/codegen/boxInline/",
     "codegen/irBoxInline/"
 )
+
+
+abstract class AbstractIrCodegenWasmJsInteropJsTest : BasicIrBoxTest(
+    "compiler/testData/codegen/wasmJsInterop",
+    "codegen/wasmJsInteropJs"
+)

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/abstractClassesForGeneratedTests.kt

@@ -24,11 +24,6 @@ abstract class AbstractJsCodegenInlineTest : BasicBoxTest(
     "codegen/boxInline"
 )
 
-abstract class AbstractIrCodegenWasmJsInteropJsTest : BasicBoxTest(
-    "compiler/testData/codegen/wasmJsInterop",
-    "codegen/wasmJsInteropWasm"
-)
-
 
 abstract class AbstractJsLegacyPrimitiveArraysBoxTest : BasicBoxTest(
     "compiler/testData/codegen/box/arrays/",

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

@@ -3,7 +3,7 @@
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
-package org.jetbrains.kotlin.js.test.semantics;
+package org.jetbrains.kotlin.js.test.ir.semantics;
 
 import com.intellij.testFramework.TestDataPath;
 import org.jetbrains.kotlin.test.JUnit3RunnerWithInners;
@@ -30,6 +30,11 @@ public class IrCodegenWasmJsInteropJsTestGenerated extends AbstractIrCodegenWasm
         KtTestUtil.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/codegen/boxWasmJsInterop"), Pattern.compile("^(.+)\\.kt$"), null, TargetBackend.JS_IR, true);
     }
 
+    @TestMetadata("externalTypeOperators.kt")
+    public void testExternalTypeOperators() throws Exception {
+        runTest("compiler/testData/codegen/boxWasmJsInterop/externalTypeOperators.kt");
+    }
+
     @TestMetadata("externals.kt")
     public void testExternals() throws Exception {
         runTest("compiler/testData/codegen/boxWasmJsInterop/externals.kt");
@@ -39,4 +44,9 @@ public class IrCodegenWasmJsInteropJsTestGenerated extends AbstractIrCodegenWasm
     public void testJsExport() throws Exception {
         runTest("compiler/testData/codegen/boxWasmJsInterop/jsExport.kt");
     }
+
+    @TestMetadata("types.kt")
+    public void testTypes() throws Exception {
+        runTest("compiler/testData/codegen/boxWasmJsInterop/types.kt");
+    }
 }

js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/wasm/semantics/IrCodegenWasmJsInteropWasmTestGenerated.java

@@ -30,6 +30,11 @@ public class IrCodegenWasmJsInteropWasmTestGenerated extends AbstractIrCodegenWa
         KtTestUtil.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/codegen/boxWasmJsInterop"), Pattern.compile("^(.+)\\.kt$"), null, TargetBackend.WASM, true);
     }
 
+    @TestMetadata("externalTypeOperators.kt")
+    public void testExternalTypeOperators() throws Exception {
+        runTest("compiler/testData/codegen/boxWasmJsInterop/externalTypeOperators.kt");
+    }
+
     @TestMetadata("externals.kt")
     public void testExternals() throws Exception {
         runTest("compiler/testData/codegen/boxWasmJsInterop/externals.kt");
@@ -39,4 +44,14 @@ public class IrCodegenWasmJsInteropWasmTestGenerated extends AbstractIrCodegenWa
     public void testJsExport() throws Exception {
         runTest("compiler/testData/codegen/boxWasmJsInterop/jsExport.kt");
     }
+
+    @TestMetadata("nullableExternRefs.kt")
+    public void testNullableExternRefs() throws Exception {
+        runTest("compiler/testData/codegen/boxWasmJsInterop/nullableExternRefs.kt");
+    }
+
+    @TestMetadata("types.kt")
+    public void testTypes() throws Exception {
+        runTest("compiler/testData/codegen/boxWasmJsInterop/types.kt");
+    }
 }

libraries/stdlib/wasm/internal/kotlin/wasm/internal/ExternalWrapper.kt

@@ -0,0 +1,191 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.wasm.internal
+
+import kotlin.wasm.internal.reftypes.anyref
+
+internal external interface ExternalInterfaceType
+
+internal class JsExternalBox(val ref: ExternalInterfaceType) {
+    override fun toString(): String =
+        externrefToString(ref)
+
+    override fun equals(other: Any?): Boolean =
+        if (other is JsExternalBox) {
+            externrefEquals(ref, other.ref)
+        } else {
+            false
+        }
+
+    override fun hashCode(): Int =
+        externrefHashCode(ref)
+}
+
+//language=js
+@JsFun("""
+(() => {
+const dataView = new DataView(new ArrayBuffer(8));
+function numberHashCode(obj) {
+    if ((obj | 0) === obj) {
+        return obj | 0;
+    } else {
+        dataView.setFloat64(0, obj, true);
+        return (dataView.getInt32(0, true) * 31 | 0) + dataView.getInt32(4, true) | 0;
+    }
+}
+
+const hashCodes = new WeakMap();
+function getObjectHashCode(obj) {
+    const res = hashCodes.get(obj);
+    if (res === undefined) {
+        const POW_2_32 = 4294967296;
+        const hash = (Math.random() * POW_2_32) | 0;
+        hashCodes.set(obj, hash);
+        return hash;
+    }
+    return res;
+}
+
+function getStringHashCode(str) {
+    var hash = 0;
+    for (var i = 0; i < str.length; i++) {
+        var code  = str.charCodeAt(i);
+        hash  = (hash * 31 + code) | 0;
+    }
+    return hash;
+}
+
+return (obj) => {
+    if (obj == null) {
+        return 0;
+    }
+    switch (typeof obj) {
+        case "object":
+        case "function":
+            return getObjectHashCode(obj);
+        case "number":
+            return numberHashCode(obj);
+        case "boolean":
+            return obj;
+        default:
+            return getStringHashCode(String(obj)); 
+    }
+}
+})()"""
+)
+private external fun externrefHashCode(ref: ExternalInterfaceType): Int
+
+@JsFun("ref => String(ref)")
+private external fun externrefToString(ref: ExternalInterfaceType): String
+
+@JsFun("(lhs, rhs) => lhs === rhs")
+private external fun externrefEquals(lhs: ExternalInterfaceType, rhs: ExternalInterfaceType): Boolean
+
+@JsFun("(ref) => (typeof ref !== 'object' || ref === null) ? null : (externrefBoxes.get(ref) ?? null)")
+private external fun getExternrefBoxOrNull(ref: ExternalInterfaceType): JsExternalBox?
+
+@JsFun("(ref, box) => { if (typeof ref === 'object' && ref !== null) { externrefBoxes.set(ref, box); } }")
+private external fun setExternrefBox(ref: ExternalInterfaceType, box: JsExternalBox)
+
+@WasmNoOpCast
+@Suppress("unused")
+internal fun Any?.asWasmAnyref(): anyref =
+    implementedAsIntrinsic
+
+@WasmNoOpCast
+@Suppress("unused")
+internal fun ExternalInterfaceType.externAsWasmAnyref(): anyref =
+    implementedAsIntrinsic
+
+@WasmNoOpCast
+@Suppress("unused")
+internal fun Any?.asWasmExternRef(): ExternalInterfaceType =
+    implementedAsIntrinsic
+
+
+@JsFun("(ref) => ref == null")
+internal external fun isNullish(ref: ExternalInterfaceType): Boolean
+
+internal fun externRefToAny(ref: ExternalInterfaceType): Any? {
+    // If ref is an instance of kotlin class -- return it cased to Any
+    val refAsAnyref = ref.externAsWasmAnyref()
+    if (wasm_ref_is_data(refAsAnyref)) {
+        val refAsDataRef = wasm_ref_as_data(refAsAnyref)
+        if (wasm_ref_test<Any>(refAsDataRef)) {
+            return wasm_ref_cast<Any>(refAsDataRef)
+        }
+    }
+
+    if (isNullish(ref))
+        return null
+
+    // If we already have a box -- return it,
+    // otherwise -- create a new box and remember it.
+    return getExternrefBoxOrNull(ref)
+        ?: JsExternalBox(ref).also {
+            setExternrefBox(ref, it)
+        }
+}
+
+
+internal fun anyToExternRef(x: Any): ExternalInterfaceType {
+    return if (x is JsExternalBox)
+        x.ref
+    else
+        x.asWasmExternRef()
+}
+
+internal external fun importStringFromWasm(addr: Int): ExternalInterfaceType
+
+@JsFun("x => x.length")
+internal external fun stringLength(x: ExternalInterfaceType): Int
+
+internal fun convertJsStringToKotlinString(x: ExternalInterfaceType): String {
+    val length = stringLength(x)
+    val addr = unsafeGetScratchRawMemory(INT_SIZE_BYTES + length * CHAR_SIZE_BYTES)
+    jsWriteStringIntoMemory(x, addr)
+    return kotlin.String(unsafeRawMemoryToCharArray(addr, length))
+}
+
+
+//language=js
+@JsFun(
+""" (str, addr) => { 
+    const memory = new DataView(wasmInstance.exports.memory.buffer);
+    for (var i = 0; i < str.length; i++) {
+        memory.setInt16(addr + i * 2, str.charCodeAt(i), true);
+    }
+}
+"""
+)
+internal external fun jsWriteStringIntoMemory(str: ExternalInterfaceType, addr: Int)
+
+
+internal fun kotlinToJsStringAdapter(x: String): ExternalInterfaceType {
+    return importStringFromWasm(exportString(x))
+}
+
+@JsFun("() => true")
+internal external fun jsTrue(): ExternalInterfaceType
+
+@JsFun("() => false")
+internal external fun jsFalse(): ExternalInterfaceType
+
+internal fun kotlinToJsBooleanAdapter(x: Boolean): ExternalInterfaceType =
+    if (x) jsTrue() else jsFalse()
+
+internal fun kotlinToJsAnyAdapter(x: Any): ExternalInterfaceType =
+    anyToExternRef(x)
+
+internal fun jsToKotlinAnyAdapter(x: ExternalInterfaceType): Any? =
+    externRefToAny(x)
+
+internal fun jsToKotlinStringAdapter(x: ExternalInterfaceType): String =
+    convertJsStringToKotlinString(x)
+
+internal fun jsToKotlinByteAdapter(x: Int): Byte = x.toByte()
+internal fun jsToKotlinShortAdapter(x: Int): Short = x.toShort()
+internal fun jsToKotlinCharAdapter(x: Int): Char = x.toChar()

libraries/stdlib/wasm/internal/kotlin/wasm/internal/WasmInstructions.kt

@@ -9,6 +9,11 @@
 
 package kotlin.wasm.internal
 
+import kotlin.wasm.internal.reftypes.anyref
+import kotlin.wasm.internal.reftypes.dataref
+import kotlin.wasm.internal.reftypes.funcref
+import kotlin.wasm.internal.reftypes.i31ref
+
 @WasmOp(WasmOp.UNREACHABLE)
 internal fun wasm_unreachable(): Nothing =
     implementedAsIntrinsic
@@ -329,4 +334,25 @@ public external fun wasm_i64_clz(a: Long): Long
 public external fun wasm_i64_popcnt(a: Long): Long
 
 @WasmOp(WasmOp.I64_CTZ)
-public external fun wasm_i64_ctz(a: Long): Long
+public external fun wasm_i64_ctz(a: Long): Long
+
+
+// Reference type operators
+
+@WasmOp(WasmOp.REF_IS_FUNC)
+internal external fun wasm_ref_is_func(x: anyref): Boolean
+
+@WasmOp(WasmOp.REF_IS_DATA)
+internal external fun wasm_ref_is_data(x: anyref): Boolean
+
+@WasmOp(WasmOp.REF_IS_I31)
+internal external fun wasm_ref_is_i31(x: anyref): Boolean
+
+@WasmOp(WasmOp.REF_AS_FUNC)
+internal external fun wasm_ref_as_func(x: anyref): funcref
+
+@WasmOp(WasmOp.REF_AS_DATA)
+internal external fun wasm_ref_as_data(x: anyref): dataref
+
+@WasmOp(WasmOp.REF_AS_I31)
+internal external fun wasm_ref_as_i31(x: anyref): i31ref

libraries/stdlib/wasm/internal/kotlin/wasm/internal/reftypes/WasmReferenceTypes.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+@file:ExcludedFromCodegen
+
+package kotlin.wasm.internal.reftypes
+
+import kotlin.wasm.internal.*
+
+// These interfaces correspond to Wasm GC reference types with the same name.
+// They are not proper Kotlin interfaces and should be used with care.
+//
+// WARNING! Do not upcast to Any, nullable types, type parameters, etc.
+//          Do not use Any methods
+//          Do not use type operators `is`, `as`, etc.
+//          Do not use ==, ===
+//
+// Use dedicated intrinsics instead.
+
+internal interface anyref
+internal interface eqref : anyref
+internal interface dataref : eqref
+internal interface i31ref : eqref
+internal interface funcref : anyref

libraries/stdlib/wasm/src/generated/_WasmOp.kt

@@ -216,6 +216,12 @@ internal annotation class WasmOp(val name: String) {
         const val RETURN = "RETURN"
         const val CALL = "CALL"
         const val CALL_INDIRECT = "CALL_INDIRECT"
+        const val TRY = "TRY"
+        const val CATCH = "CATCH"
+        const val CATCH_ALL = "CATCH_ALL"
+        const val DELEGATE = "DELEGATE"
+        const val THROW = "THROW"
+        const val RETHROW = "RETHROW"
         const val DROP = "DROP"
         const val SELECT = "SELECT"
         const val SELECT_TYPED = "SELECT_TYPED"
@@ -255,5 +261,19 @@ internal annotation class WasmOp(val name: String) {
         const val REF_TEST = "REF_TEST"
         const val REF_CAST = "REF_CAST"
         const val BR_ON_CAST = "BR_ON_CAST"
+        const val BR_ON_CAST_FAIL = "BR_ON_CAST_FAIL"
+        const val REF_IS_FUNC = "REF_IS_FUNC"
+        const val REF_IS_DATA = "REF_IS_DATA"
+        const val REF_IS_I31 = "REF_IS_I31"
+        const val REF_AS_FUNC = "REF_AS_FUNC"
+        const val REF_AS_DATA = "REF_AS_DATA"
+        const val REF_AS_I31 = "REF_AS_I31"
+        const val BR_ON_FUNC = "BR_ON_FUNC"
+        const val BR_ON_DATA = "BR_ON_DATA"
+        const val BR_ON_I31 = "BR_ON_I31"
+        const val BR_ON_NON_FUNC = "BR_ON_NON_FUNC"
+        const val BR_ON_NON_DATA = "BR_ON_NON_DATA"
+        const val BR_ON_NON_I31 = "BR_ON_NON_I31"
+        const val GET_UNIT = "GET_UNIT"
     }
 }

libraries/stdlib/wasm/src/kotlin/js/annotations.kt

@@ -13,4 +13,18 @@ package kotlin.js
 @ExperimentalJsExport
 @Retention(AnnotationRetention.BINARY)
 @Target(AnnotationTarget.FUNCTION)
-public actual annotation class JsExport
+public actual annotation class JsExport
+
+/**
+ * Specifies JavaScript name for external and imported declarations
+ */
+@Retention(AnnotationRetention.BINARY)
+@Target(
+    AnnotationTarget.CLASS,
+    AnnotationTarget.FUNCTION,
+    AnnotationTarget.PROPERTY,
+    AnnotationTarget.CONSTRUCTOR,
+    AnnotationTarget.PROPERTY_GETTER,
+    AnnotationTarget.PROPERTY_SETTER
+)
+public actual annotation class JsName(actual val name: String)

wasm/wasm.ir/src/org/jetbrains/kotlin/wasm/ir/Operators.kt

@@ -368,6 +368,23 @@ enum class WasmOp(
 
     BR_ON_CAST("br_on_cast", 0xFB_42, listOf(LABEL_IDX)),
 
+    BR_ON_CAST_FAIL("br_on_cast_fail", 0xfb43, listOf(LABEL_IDX)),
+
+    REF_IS_FUNC("ref.is_func", 0xfb50),
+    REF_IS_DATA("ref.is_data", 0xfb51),
+    REF_IS_I31("ref.is_i31", 0xfb52),
+    REF_AS_FUNC("ref.as_func", 0xfb58),
+    REF_AS_DATA("ref.as_data", 0xfb59),
+    REF_AS_I31("ref.as_i31", 0xfb5a),
+
+    BR_ON_FUNC("br_on_func", 0xfb60, listOf(LABEL_IDX)),
+    BR_ON_DATA("br_on_data", 0xfb61, listOf(LABEL_IDX)),
+    BR_ON_I31("br_on_i31", 0xfb62, listOf(LABEL_IDX)),
+
+    BR_ON_NON_FUNC("br_on_non_func", 0xfb63, listOf(LABEL_IDX)),
+    BR_ON_NON_DATA("br_on_non_data", 0xfb64, listOf(LABEL_IDX)),
+    BR_ON_NON_I31("br_on_non_i31", 0xfb65, listOf(LABEL_IDX)),
+
     // Pseudo-instruction, just alias for a normal call. It's used to easily spot get_unit on the wasm level.
     GET_UNIT("call", 0x10, FUNC_IDX)
     ;