[Wasm] Add interop annotation @JsFun

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

@@ -99,14 +99,6 @@ fun compileWasm(
 fun WasmCompiledModuleFragment.generateJs(): String {
     val runtime = """
     const runtime = {
-        String_plus(str1, str2) {
-            return str1 + String(str2);
-        },
-
-        String_getLength(str) {
-            return str.length;
-        },
-
         String_getChar(str, index) {
             return str.charCodeAt(index);
         },
@@ -163,5 +155,8 @@ fun WasmCompiledModuleFragment.generateJs(): String {
     };
     """.trimIndent()
 
-    return runtime + generateStringLiteralsSupport(stringLiterals)
+    val jsCode =
+        "\nconst js_code = {${jsFuns.joinToString(",\n") { "\"" + it.importName + "\" : " + it.jsCode }}};"
+
+    return runtime + generateStringLiteralsSupport(stringLiterals) + jsCode
 }

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

@@ -208,7 +208,7 @@ class BodyGenerator(val context: WasmFunctionCodegenContext) : IrElementVisitorV
 
         // 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) {
+        if (function.getWasmImportAnnotation() != null || function.getJsFunAnnotation() != null) {
             val resT = context.transformResultType(function.returnType)
             if (resT is WasmRefNullType) {
                 generateTypeRTT(function.returnType)

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

@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.backend.wasm.ir2wasm
 
 import org.jetbrains.kotlin.backend.common.ir.isOverridableOrOverrides
 import org.jetbrains.kotlin.backend.wasm.WasmBackendContext
+import org.jetbrains.kotlin.backend.wasm.lower.wasmSignature
 import org.jetbrains.kotlin.backend.wasm.utils.*
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
 import org.jetbrains.kotlin.descriptors.Modality
@@ -35,12 +36,23 @@ class DeclarationGenerator(val context: WasmModuleCodegenContext) : IrElementVis
         // Type aliases are not material
     }
 
+    private fun jsCodeName(declaration: IrFunction): String {
+        return declaration.fqNameWhenAvailable!!.asString() + "_" + (declaration as IrSimpleFunction).wasmSignature(irBuiltIns).hashCode()
+    }
+
     override fun visitFunction(declaration: IrFunction) {
         // Inline class constructors are currently empty
         if (declaration is IrConstructor && backendContext.inlineClassesUtils.isClassInlineLike(declaration.parentAsClass))
             return
 
-        val importedName = declaration.getWasmImportAnnotation()
+        val jsCode = declaration.getJsFunAnnotation()
+        val importedName = if (jsCode != null) {
+            val jsCodeName = jsCodeName(declaration)
+            context.addJsFun(jsCodeName, jsCode)
+            WasmImportPair("js_code", jsCodeName(declaration))
+        } else {
+            declaration.getWasmImportAnnotation()
+        }
 
         val isIntrinsic = declaration.hasWasmReinterpretAnnotation() || declaration.getWasmOpAnnotation() != null
         if (isIntrinsic) {

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

@@ -46,7 +46,10 @@ class WasmCompiledModuleFragment {
         ReferencableAndDefinable<IrClassSymbol, ConstantDataElement>()
     val exports = mutableListOf<WasmExport<*>>()
 
-    //
+    class JsCodeSnippet(val importName: String, val jsCode: String)
+
+    val jsFuns = mutableListOf<JsCodeSnippet>()
+
     var startFunction: WasmFunction? = null
 
     open class ReferencableElements<Ir, Wasm : Any> {

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

@@ -22,6 +22,7 @@ interface WasmModuleCodegenContext : WasmBaseCodegenContext {
     fun defineStructType(irClass: IrClassSymbol, wasmStruct: WasmStructDeclaration)
     fun defineRTT(irClass: IrClassSymbol, wasmGlobal: WasmGlobal)
     fun defineFunctionType(irFunction: IrFunctionSymbol, wasmFunctionType: WasmFunctionType)
+    fun addJsFun(importName: String, jsCode: String)
 
     fun setStartFunction(wasmFunction: WasmFunction)
     fun addExport(wasmExport: WasmExport<*>)

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

@@ -166,4 +166,9 @@ class WasmModuleCodegenContextImpl(
         val fieldId = metadata.fields.indexOf(field)
         return WasmSymbol(fieldId)
     }
+
+    override fun addJsFun(importName: String, jsCode: String) {
+        wasmFragment.jsFuns +=
+            WasmCompiledModuleFragment.JsCodeSnippet(importName = importName, jsCode = jsCode)
+    }
 }

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

@@ -35,3 +35,6 @@ fun IrAnnotationContainer.getWasmImportAnnotation(): WasmImportPair? =
             (it.getValueArgument(1) as IrConst<*>).value as String
         )
     }
+
+fun IrAnnotationContainer.getJsFunAnnotation(): String? =
+    getAnnotation(FqName("kotlin.JsFun"))?.getSingleConstStringArgument()