[FIR JS] Report NESTED_JS_EXPORT

compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirJsDiagnosticsList.kt

@@ -96,6 +96,10 @@ object JS_DIAGNOSTICS_LIST : DiagnosticList("FirJsErrors") {
         val EXTERNAL_INTERFACE_AS_CLASS_LITERAL by error<KtElement>()
     }
 
+    val EXPORT by object : DiagnosticGroup("Export") {
+        val NESTED_JS_EXPORT by error<KtElement>()
+    }
+
     val DYNAMICS by object : DiagnosticGroup("Dynamics") {
         val DELEGATION_BY_DYNAMIC by error<KtElement>()
     }

compiler/fir/checkers/checkers.js/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/js/FirJsErrors.kt

@@ -79,6 +79,9 @@ object FirJsErrors {
     val UNCHECKED_CAST_TO_EXTERNAL_INTERFACE by warning2<KtElement, ConeKotlinType, ConeKotlinType>()
     val EXTERNAL_INTERFACE_AS_CLASS_LITERAL by error0<KtElement>()
 
+    // Export
+    val NESTED_JS_EXPORT by error0<KtElement>()
+
     // Dynamics
     val DELEGATION_BY_DYNAMIC by error0<KtElement>()
 

compiler/fir/checkers/checkers.js/src/org/jetbrains/kotlin/fir/analysis/diagnostics/js/FirJsErrorsDefaultMessages.kt

@@ -44,6 +44,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.js.FirJsErrors.NATIVE_INDEX
 import org.jetbrains.kotlin.fir.analysis.diagnostics.js.FirJsErrors.NATIVE_SETTER_WRONG_RETURN_TYPE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.js.FirJsErrors.NESTED_CLASS_IN_EXTERNAL_INTERFACE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.js.FirJsErrors.NESTED_EXTERNAL_DECLARATION
+import org.jetbrains.kotlin.fir.analysis.diagnostics.js.FirJsErrors.NESTED_JS_EXPORT
 import org.jetbrains.kotlin.fir.analysis.diagnostics.js.FirJsErrors.NON_ABSTRACT_MEMBER_OF_EXTERNAL_INTERFACE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.js.FirJsErrors.NON_EXTERNAL_DECLARATION_IN_INAPPROPRIATE_FILE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.js.FirJsErrors.OVERRIDING_EXTERNAL_FUN_WITH_OPTIONAL_PARAMS
@@ -167,6 +168,7 @@ object FirJsErrorsDefaultMessages : BaseDiagnosticRendererFactory() {
             FirDiagnosticRenderers.RENDER_TYPE,
         )
         map.put(EXTERNAL_INTERFACE_AS_CLASS_LITERAL, "Can't refer to external interface from class literal")
+        map.put(NESTED_JS_EXPORT, "@JsExport is only allowed on files and top-level declarations")
 
         map.checkMissingMessages(FirJsErrors)
     }

compiler/fir/checkers/checkers.js/src/org/jetbrains/kotlin/fir/analysis/js/checkers/JsDeclarationCheckers.kt

@@ -27,6 +27,7 @@ object JsDeclarationCheckers : DeclarationCheckers() {
             FirJsExternalChecker,
             FirJsExternalFileChecker,
             FirJsNameChecker,
+            FirJsExportAnnotationChecker,
         )
 
     override val classCheckers: Set<FirClassChecker>

compiler/fir/checkers/checkers.js/src/org/jetbrains/kotlin/fir/analysis/js/checkers/declaration/FirJsExportAnnotationChecker.kt

@@ -0,0 +1,27 @@
+/*
+ * 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.js.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.js.FirJsErrors
+import org.jetbrains.kotlin.fir.declarations.FirDeclaration
+import org.jetbrains.kotlin.fir.declarations.FirFile
+import org.jetbrains.kotlin.fir.declarations.getAnnotationByClassId
+import org.jetbrains.kotlin.name.JsStandardClassIds
+
+object FirJsExportAnnotationChecker : FirBasicDeclarationChecker() {
+    override fun check(declaration: FirDeclaration, context: CheckerContext, reporter: DiagnosticReporter) {
+        val jsExport = declaration.getAnnotationByClassId(JsStandardClassIds.Annotations.JsExport, context.session) ?: return
+
+        if (declaration !is FirFile && !context.isTopLevel) {
+            reporter.reportOn(jsExport.source, FirJsErrors.NESTED_JS_EXPORT, context)
+        }
+    }
+}