[JS IR] Make JsExport not fail on companion objects (KT-37829)

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/export/ExportModelGenerator.kt

@@ -171,8 +171,11 @@ class ExportModelGenerator(val context: JsIrBackendContext) {
                 }
 
                 is IrField -> {
-                    assert(candidate.correspondingPropertySymbol != null) {
-                        "Properties without fields are not supported ${candidate.fqNameWhenAvailable}"
+                    assert(
+                        candidate.origin == IrDeclarationOrigin.FIELD_FOR_OBJECT_INSTANCE
+                                || candidate.correspondingPropertySymbol != null
+                    ) {
+                        "Unexpected field without property ${candidate.fqNameWhenAvailable}"
                     }
                 }
 

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/ObjectLowering.kt

@@ -19,10 +19,7 @@ import org.jetbrains.kotlin.ir.backend.js.ir.JsIrBuilder
 import org.jetbrains.kotlin.ir.builders.*
 import org.jetbrains.kotlin.ir.builders.declarations.buildField
 import org.jetbrains.kotlin.ir.builders.declarations.buildFun
-import org.jetbrains.kotlin.ir.declarations.IrClass
-import org.jetbrains.kotlin.ir.declarations.IrConstructor
-import org.jetbrains.kotlin.ir.declarations.IrDeclaration
-import org.jetbrains.kotlin.ir.declarations.IrVariable
+import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.types.makeNullable
 import org.jetbrains.kotlin.ir.util.*
@@ -47,6 +44,7 @@ class ObjectDeclarationLowering(
             name = Name.identifier(declaration.name.asString() + "_instance")
             type = declaration.defaultType.makeNullable()
             isStatic = true
+            origin = IrDeclarationOrigin.FIELD_FOR_OBJECT_INSTANCE
         }.apply {
             parent = declaration.parent
             initializer = null  // Initialized with 'undefined'

js/js.translator/testData/typescript-export/declarations/declarations.d.ts

@@ -49,5 +49,11 @@ declare namespace JS_TESTS {
             foo(): number;
         };
         function takesO(o: typeof foo.O): number;
+        class KT_37829 {
+            constructor();
+            readonly Companion: {
+                readonly x: number;
+            };
+        }
     }
 }

js/js.translator/testData/typescript-export/declarations/declarations.kt

@@ -93,4 +93,12 @@ object O {
 }
 
 fun takesO(o: O): Int =
-    O.x + O.foo()
+    O.x + O.foo()
+
+// Test that JsExport with companion object compiles without error.
+// Usage is not supported yet.
+class KT_37829 {
+    companion object {
+        val x = 10
+    }
+}