Spec: Add missing last-column-id

core/src/main/java/org/apache/iceberg/MetadataUpdateParser.java

@@ -397,7 +397,12 @@ private static MetadataUpdate readUpgradeFormatVersion(JsonNode node) {
   private static MetadataUpdate readAddSchema(JsonNode node) {
     JsonNode schemaNode = JsonUtil.get(SCHEMA, node);
     Schema schema = SchemaParser.fromJson(schemaNode);
-    int lastColumnId = JsonUtil.getInt(LAST_COLUMN_ID, node);
+    int lastColumnId;
+    if (node.has(LAST_COLUMN_ID)) {
+      lastColumnId = JsonUtil.getInt(LAST_COLUMN_ID, node);
+    } else {
+      lastColumnId = schema.highestFieldId();
+    }
     return new MetadataUpdate.AddSchema(schema, lastColumnId);
   }
 

core/src/test/java/org/apache/iceberg/TestMetadataUpdateParser.java

@@ -123,6 +123,17 @@ public void testAddSchemaFromJson() {
     assertEquals(action, actualUpdate, MetadataUpdateParser.fromJson(json));
   }
 
+  @Test
+  public void testAddSchemaFromJsonWithoutLastColumnId() {
+    String action = MetadataUpdateParser.ADD_SCHEMA;
+    Schema schema = ID_DATA_SCHEMA;
+    int lastColumnId = schema.highestFieldId();
+    String json =
+        String.format("{\"action\":\"add-schema\",\"schema\":%s}", SchemaParser.toJson(schema));
+    MetadataUpdate actualUpdate = new MetadataUpdate.AddSchema(schema, lastColumnId);
+    assertEquals(action, actualUpdate, MetadataUpdateParser.fromJson(json));
+  }
+
   @Test
   public void testAddSchemaToJson() {
     Schema schema = ID_DATA_SCHEMA;

open-api/rest-catalog-open-api.yaml

@@ -1500,6 +1500,9 @@ components:
           properties:
             schema:
               $ref: '#/components/schemas/Schema'
+            last-column-id:
+              type: integer
+              description: The highest assigned column ID for the table. This is used to ensure columns are always assigned an unused ID when evolving schemas.
 
     SetCurrentSchemaUpdate:
       allOf: