[Wasm] Add @JsFun diagnostics (KT-56944)

JsFun target should be top-level external function

compiler/testData/diagnostics/wasmTests/jsInterop/jsFun.kt

@@ -0,0 +1,15 @@
+@JsFun("() => {}")
+external fun topLevelExternalFun(): Unit
+
+external class ExternalClass {
+    <!WRONG_JS_FUN_TARGET!>@JsFun("() => {}")<!>
+    fun memberFun(): Unit
+}
+
+<!WRONG_JS_FUN_TARGET!>@JsFun("() => {}")<!>
+fun topLevelNonExternalFun(): Unit {}
+
+class NonExternalClass {
+    <!WRONG_JS_FUN_TARGET!>@JsFun("() => {}")<!>
+    fun memberFun(): Unit {}
+}

wasm/wasm.frontend/src/org/jetbrains/kotlin/wasm/resolve/WasmPlatformConfigurator.kt

@@ -18,6 +18,7 @@ import org.jetbrains.kotlin.resolve.checkers.ExpectedActualDeclarationChecker
 import org.jetbrains.kotlin.wasm.resolve.diagnostics.WasmExternalDeclarationChecker
 import org.jetbrains.kotlin.wasm.resolve.diagnostics.WasmExternalInheritanceChecker
 import org.jetbrains.kotlin.wasm.resolve.diagnostics.WasmImportAnnotationChecker
+import org.jetbrains.kotlin.wasm.resolve.diagnostics.WasmJsFunAnnotationChecker
 
 // TODO: Review the list of used K/JS checkers.
 //       Refactor useful checkers into common module.
@@ -30,6 +31,7 @@ object WasmPlatformConfigurator : PlatformConfiguratorBase(
         JsExportDeclarationChecker,
         WasmExternalDeclarationChecker,
         WasmImportAnnotationChecker,
+        WasmJsFunAnnotationChecker,
     ),
     additionalCallCheckers = listOf(
         JsModuleCallChecker,

wasm/wasm.frontend/src/org/jetbrains/kotlin/wasm/resolve/diagnostics/DefaultErrorMessagesWasm.kt

@@ -23,6 +23,8 @@ private val DIAGNOSTIC_FACTORY_TO_RENDERER by lazy {
         put(ErrorsWasm.WASM_IMPORT_VARARG_PARAMETER, "Vararg parameters are not supported with @WasmImport")
         put(ErrorsWasm.WASM_IMPORT_UNSUPPORTED_PARAMETER_TYPE, "Unsupported @WasmImport parameter type {0}", Renderers.RENDER_TYPE)
         put(ErrorsWasm.WASM_IMPORT_UNSUPPORTED_RETURN_TYPE, "Unsupported @WasmImport return type {0}", Renderers.RENDER_TYPE)
+
+        put(ErrorsWasm.WRONG_JS_FUN_TARGET, "Only top-level external functions can be implemented using @JsFun")
     }
 }
 

wasm/wasm.frontend/src/org/jetbrains/kotlin/wasm/resolve/diagnostics/ErrorsWasm.java

@@ -26,6 +26,8 @@ public interface ErrorsWasm {
     DiagnosticFactory1<PsiElement, KotlinType> WASM_IMPORT_UNSUPPORTED_PARAMETER_TYPE = DiagnosticFactory1.create(ERROR);
     DiagnosticFactory1<PsiElement, KotlinType> WASM_IMPORT_UNSUPPORTED_RETURN_TYPE = DiagnosticFactory1.create(ERROR);
 
+    DiagnosticFactory0<PsiElement> WRONG_JS_FUN_TARGET = DiagnosticFactory0.create(ERROR);
+
     @SuppressWarnings("UnusedDeclaration")
     Object _initializer = new Object() {
         {

wasm/wasm.frontend/src/org/jetbrains/kotlin/wasm/resolve/diagnostics/WasmJsFunAnnotationChecker.kt

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2010-2016 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.wasm.resolve.diagnostics
+
+import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.psi.KtDeclaration
+import org.jetbrains.kotlin.resolve.DescriptorUtils
+import org.jetbrains.kotlin.resolve.checkers.DeclarationChecker
+import org.jetbrains.kotlin.resolve.checkers.DeclarationCheckerContext
+import org.jetbrains.kotlin.resolve.descriptorUtil.isEffectivelyExternal
+import org.jetbrains.kotlin.resolve.source.getPsi
+
+// TODO: Implement in K2: KT-56849
+object WasmJsFunAnnotationChecker : DeclarationChecker {
+    private val jsFunFqName = FqName("kotlin.JsFun")
+
+    override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
+        if (descriptor !is MemberDescriptor) return
+        val jsFun = descriptor.annotations.findAnnotation(jsFunFqName) ?: return
+        if (!descriptor.isEffectivelyExternal() || !DescriptorUtils.isTopLevelDeclaration(descriptor)) {
+            val jsFunPsi = jsFun.source.getPsi() ?: declaration
+            context.trace.report(ErrorsWasm.WRONG_JS_FUN_TARGET.on(jsFunPsi))
+        }
+    }
+}

wasm/wasm.tests/tests-gen/org/jetbrains/kotlin/wasm/test/diagnostics/DiagnosticsWasmTestGenerated.java

@@ -56,6 +56,12 @@ public class DiagnosticsWasmTestGenerated extends AbstractDiagnosticsWasmTest {
         public void testJsExport() throws Exception {
             runTest("compiler/testData/diagnostics/wasmTests/jsInterop/jsExport.kt");
         }
+
+        @Test
+        @TestMetadata("jsFun.kt")
+        public void testJsFun() throws Exception {
+            runTest("compiler/testData/diagnostics/wasmTests/jsInterop/jsFun.kt");
+        }
     }
 
     @Nested