Make StripTypeAliasDeclarationsLowering a DeclarationTransformer

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/StripTypeAliasDeclarationsLowering.kt

@@ -5,40 +5,13 @@
 
 package org.jetbrains.kotlin.backend.common.lower
 
-import org.jetbrains.kotlin.backend.common.FileLoweringPass
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.declarations.IrClass
-import org.jetbrains.kotlin.ir.declarations.IrFile
+import org.jetbrains.kotlin.backend.common.DeclarationTransformer
+import org.jetbrains.kotlin.ir.declarations.IrDeclaration
 import org.jetbrains.kotlin.ir.declarations.IrTypeAlias
-import org.jetbrains.kotlin.ir.expressions.IrContainerExpression
-import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
-import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
-import org.jetbrains.kotlin.ir.visitors.acceptVoid
 
-class StripTypeAliasDeclarationsLowering :
-    IrElementVisitorVoid,
-    FileLoweringPass {
+class StripTypeAliasDeclarationsLowering : DeclarationTransformer {
 
-    override fun lower(irFile: IrFile) {
-        irFile.acceptVoid(this)
-    }
-
-    override fun visitElement(element: IrElement) {
-        element.acceptChildrenVoid(this)
-    }
-
-    override fun visitFile(declaration: IrFile) {
-        declaration.acceptChildrenVoid(this)
-        declaration.declarations.removeAll { it is IrTypeAlias }
-    }
-
-    override fun visitClass(declaration: IrClass) {
-        declaration.acceptChildrenVoid(this)
-        declaration.declarations.removeAll { it is IrTypeAlias }
-    }
-
-    override fun visitContainerExpression(expression: IrContainerExpression) {
-        expression.acceptChildrenVoid(this)
-        expression.statements.removeAll { it is IrTypeAlias }
+    override fun transformFlat(declaration: IrDeclaration): List<IrDeclaration>? {
+        return if (declaration is IrTypeAlias) listOf() else null
     }
 }