[IR SERIALIZATION] Fix clashes

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

@@ -6,23 +6,36 @@
 package org.jetbrains.kotlin.ir.backend.js.lower.serialization.ir
 
 import org.jetbrains.kotlin.backend.common.serialization.*
+import org.jetbrains.kotlin.descriptors.PropertyDescriptor
 import org.jetbrains.kotlin.ir.declarations.IrDeclaration
+import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
+import org.jetbrains.kotlin.ir.declarations.IrTypeParameter
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
 import org.jetbrains.kotlin.ir.util.render
 
-class JsUniqIdClashTracker: UniqIdClashTracker {
-    private val commitedUniqIds = mutableMapOf<UniqId, IrDeclaration>()
+class JsUniqIdClashTracker : UniqIdClashTracker {
+    private val committedUniqIds = mutableMapOf<UniqId, IrDeclaration>()
 
     override fun commit(declaration: IrDeclaration, uniqId: UniqId) {
         if (uniqId.isLocal) return // don't track local ids
 
-        if (uniqId in commitedUniqIds) {
-            val clashedDeclaration = commitedUniqIds[uniqId]!!
-            // TODO: handle clashes properly
-            error("UniqId clash: $uniqId; Existed declaration ${clashedDeclaration.render()} clashed with new ${declaration.render()}")
+        if (uniqId in committedUniqIds) {
+            val clashedDeclaration = committedUniqIds[uniqId]!!
+            if (declaration !is IrTypeParameter && declaration.descriptor.containingDeclaration !is PropertyDescriptor) {
+                // TODO: handle clashes properly
+                error("UniqId clash: $uniqId; Existed declaration ${clashedDeclaration.render()} clashed with new ${declaration.render()}")
+            } else {
+                // Check whether they are type parameters of the same extension property but different accessors
+                val parent = declaration.parent
+                val clashedParent = clashedDeclaration.parent
+                require(parent is IrSimpleFunction)
+                require(clashedParent is IrSimpleFunction)
+                require(clashedDeclaration !== parent)
+                require(clashedParent.correspondingPropertySymbol === parent.correspondingPropertySymbol)
+            }
         }
 
-        commitedUniqIds[uniqId] = declaration
+        committedUniqIds[uniqId] = declaration
     }
 }