[Wasm] Port @JsFun checker to K2 (KT-56849)

^KT-62724 Fixed

compiler/fir/checkers/checkers.wasm/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/wasm/FirWasmErrors.kt

@@ -23,6 +23,9 @@ object FirWasmErrors {
     val CALL_TO_DEFINED_EXTERNALLY_FROM_NON_EXTERNAL_DECLARATION by error0<PsiElement>()
     val WRONG_JS_INTEROP_TYPE by error2<KtElement, String, ConeKotlinType>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE_OR_DEFAULT)
 
+    // JsFun
+    val WRONG_JS_FUN_TARGET by error0<PsiElement>()
+
     // Wasm interop
     val NESTED_WASM_EXPORT by error0<KtElement>()
     val WASM_EXPORT_ON_EXTERNAL_DECLARATION by error0<KtElement>()

compiler/fir/checkers/checkers.wasm/src/org/jetbrains/kotlin/fir/analysis/diagnostics/wasm/FirWasmErrorsDefaultMessages.kt

@@ -23,6 +23,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.wasm.FirWasmErrors.WASM_IMP
 import org.jetbrains.kotlin.fir.analysis.diagnostics.wasm.FirWasmErrors.WASM_IMPORT_EXPORT_UNSUPPORTED_RETURN_TYPE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.wasm.FirWasmErrors.WASM_IMPORT_EXPORT_VARARG_PARAMETER
 import org.jetbrains.kotlin.fir.analysis.diagnostics.wasm.FirWasmErrors.WASM_IMPORT_ON_NON_EXTERNAL_DECLARATION
+import org.jetbrains.kotlin.fir.analysis.diagnostics.wasm.FirWasmErrors.WRONG_JS_FUN_TARGET
 import org.jetbrains.kotlin.fir.analysis.diagnostics.wasm.FirWasmErrors.WRONG_JS_INTEROP_TYPE
 
 @Suppress("unused")
@@ -45,6 +46,8 @@ object FirWasmErrorsDefaultMessages : BaseDiagnosticRendererFactory() {
             TO_STRING, FirDiagnosticRenderers.RENDER_TYPE,
         )
 
+        map.put(WRONG_JS_FUN_TARGET, "Only top-level external functions can be implemented using '@JsFun'.")
+
         map.put(NESTED_WASM_EXPORT, "Only top-level functions can be exported with '@WasmExport'.")
         map.put(WASM_EXPORT_ON_EXTERNAL_DECLARATION, "Functions annotated with '@WasmExport' must not be external.")
         map.put(JS_AND_WASM_EXPORTS_ON_SAME_DECLARATION, "Cannot use '@WasmExport' and '@JsExport' for same function.")

compiler/fir/checkers/checkers.wasm/src/org/jetbrains/kotlin/fir/analysis/wasm/checkers/WasmDeclarationCheckers.kt

@@ -20,5 +20,6 @@ object WasmDeclarationCheckers : DeclarationCheckers() {
             FirWasmImportAnnotationChecker,
             FirWasmExportAnnotationChecker,
             FirWasmExternalChecker,
+            FirWasmJsFunAnnotationChecker,
         )
 }

compiler/fir/checkers/checkers.wasm/src/org/jetbrains/kotlin/fir/analysis/wasm/checkers/declaration/FirWasmJsFunAnnotationChecker.kt

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2010-2023 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.fir.analysis.wasm.checkers.declaration
+
+import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.reportOn
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirBasicDeclarationChecker
+import org.jetbrains.kotlin.fir.analysis.checkers.isTopLevel
+import org.jetbrains.kotlin.fir.analysis.diagnostics.wasm.FirWasmErrors
+import org.jetbrains.kotlin.fir.declarations.FirDeclaration
+import org.jetbrains.kotlin.fir.declarations.getAnnotationByClassId
+import org.jetbrains.kotlin.fir.declarations.utils.isEffectivelyExternal
+import org.jetbrains.kotlin.fir.expressions.FirAnnotation
+import org.jetbrains.kotlin.name.WasmStandardClassIds
+
+object FirWasmJsFunAnnotationChecker : FirBasicDeclarationChecker() {
+    override fun check(declaration: FirDeclaration, context: CheckerContext, reporter: DiagnosticReporter) {
+        val annotation: FirAnnotation =
+            declaration.annotations.getAnnotationByClassId(WasmStandardClassIds.Annotations.JsFun, context.session) ?: return
+
+        if (!context.isTopLevel || !declaration.symbol.isEffectivelyExternal(context.session)) {
+            reporter.reportOn(annotation.source, FirWasmErrors.WRONG_JS_FUN_TARGET, context)
+        }
+    }
+}