1 files changed, 7 insertions, 4 deletions
diff --git a/formats/json/commonMain/src/kotlinx/serialization/json/internal/JsonTreeReader.kt b/formats/json/commonMain/src/kotlinx/serialization/json/internal/JsonTreeReader.kt
index 7c01daa8..9cb9bb3c 100644
--- a/formats/json/commonMain/src/kotlinx/serialization/json/internal/JsonTreeReader.kt
+++ b/formats/json/commonMain/src/kotlinx/serialization/json/internal/JsonTreeReader.kt
@@ -13,6 +13,7 @@ internal class JsonTreeReader(
     private val lexer: AbstractJsonLexer
 ) {
     private val isLenient = configuration.isLenient
+    private val trailingCommaAllowed = configuration.allowTrailingComma
     private var stackDepth = 0
 
     private fun readObject(): JsonElement = readObjectImpl {
@@ -44,8 +45,9 @@ internal class JsonTreeReader(
         if (lastToken == TC_BEGIN_OBJ) { // Case of empty object
             lexer.consumeNextToken(TC_END_OBJ)
         } else if (lastToken == TC_COMMA) { // Trailing comma
-            lexer.fail("Unexpected trailing comma")
-        }
+            if (!trailingCommaAllowed) lexer.invalidTrailingComma()
+            lexer.consumeNextToken(TC_END_OBJ)
+        } // else unexpected token?
         return JsonObject(result)
     }
 
@@ -66,7 +68,8 @@ internal class JsonTreeReader(
         if (lastToken == TC_BEGIN_LIST) { // Case of empty object
             lexer.consumeNextToken(TC_END_LIST)
         } else if (lastToken == TC_COMMA) { // Trailing comma
-            lexer.fail("Unexpected trailing comma")
+            if (!trailingCommaAllowed) lexer.invalidTrailingComma("array")
+            lexer.consumeNextToken(TC_END_LIST)
         }
         return JsonArray(result)
     }
@@ -101,7 +104,7 @@ internal class JsonTreeReader(
                 result
             }
             TC_BEGIN_LIST -> readArray()
-            else -> lexer.fail("Cannot begin reading element, unexpected token: $token")
+            else -> lexer.fail("Cannot read Json element because of unexpected ${tokenDescription(token)}")
         }
     }