From ca4c16ea50b94c2c0c190dc95f2a59c0964dc029 Mon Sep 17 00:00:00 2001
From: justavibedev <213012880+justavibedev@users.noreply.github.com>
Date: Thu, 22 Oct 2026 11:23:07 -0700
Subject: [PATCH] fix(database): initialize new island maps when resuming
 checkpoints

---
 openevolve/database.py           |  5 ++
 tests/test_checkpoint_islands.py | 88 ++++++++++++++++++++++++++++++++
 2 files changed, 93 insertions(+)
 create mode 100644 tests/test_checkpoint_islands.py

diff --git a/openevolve/database.py b/openevolve/database.py
index ab1dad21b..f06786cf4 100644
--- a/openevolve/database.py
+++ b/openevolve/database.py
@@ -856,6 +856,11 @@ def _reconstruct_islands(self, saved_islands: List[List[str]]) -> None:
         num_islands = max(len(saved_islands), self.config.num_islands)
         self.islands = [set() for _ in range(num_islands)]
 
+        # Retain saved cells and initialize maps for any newly configured islands.
+        self.island_feature_maps.extend(
+            {} for _ in range(num_islands - len(self.island_feature_maps))
+        )
+
         missing_programs = []
         restored_programs = 0
 
diff --git a/tests/test_checkpoint_islands.py b/tests/test_checkpoint_islands.py
new file mode 100644
index 000000000..c0e0e98cc
--- /dev/null
+++ b/tests/test_checkpoint_islands.py
@@ -0,0 +1,88 @@
+"""Tests for resuming checkpoints with a different configured island count."""
+
+import json
+import os
+import tempfile
+import unittest
+
+from openevolve.config import DatabaseConfig
+from openevolve.database import Program, ProgramDatabase
+
+
+class TestCheckpointIslands(unittest.TestCase):
+    def setUp(self):
+        checkpoint = tempfile.TemporaryDirectory()
+        self.addCleanup(checkpoint.cleanup)
+        self.checkpoint_path = checkpoint.name
+        self.database = ProgramDatabase(DatabaseConfig(in_memory=True, num_islands=2))
+        for island in range(2):
+            self.database.add(self.make_program(island), target_island=island)
+        self.database.save(self.checkpoint_path)
+
+    @staticmethod
+    def make_program(index):
+        return Program(
+            id=f"program_{index}",
+            code=f"def solve(): return {index}",
+            metrics={"combined_score": index + 1.0},
+        )
+
+    def load_database(self, num_islands):
+        return ProgramDatabase(
+            DatabaseConfig(
+                in_memory=True,
+                num_islands=num_islands,
+                db_path=self.checkpoint_path,
+            )
+        )
+
+    def test_resume_with_more_islands(self):
+        resumed = self.load_database(num_islands=4)
+
+        # Exercise both new islands; their feature maps must not share cells.
+        for island in (2, 3):
+            resumed.add(self.make_program(island), target_island=island)
+            self.assertEqual(resumed.islands[island], {f"program_{island}"})
+            self.assertEqual(
+                set(resumed.island_feature_maps[island].values()), {f"program_{island}"}
+            )
+
+        self.assertEqual(resumed.island_feature_maps[:2], self.database.island_feature_maps)
+        self.assertEqual(len(resumed.island_feature_maps), 4)
+        self.assertIsNot(resumed.island_feature_maps[2], resumed.island_feature_maps[3])
+        self.assertEqual(set(resumed.island_feature_maps[2].values()), {"program_2"})
+
+        resumed.save(self.checkpoint_path)
+        reloaded = ProgramDatabase(DatabaseConfig(in_memory=True, num_islands=4))
+        reloaded.load(self.checkpoint_path)
+        self.assertEqual(reloaded.island_feature_maps, resumed.island_feature_maps)
+        self.assertEqual(reloaded.islands, resumed.islands)
+
+    def test_resume_preserves_saved_islands(self):
+        for num_islands in (1, 2):
+            with self.subTest(num_islands=num_islands):
+                resumed = self.load_database(num_islands)
+                self.assertEqual(resumed.islands, self.database.islands)
+                self.assertEqual(resumed.island_feature_maps, self.database.island_feature_maps)
+                resumed.add(self.make_program(2), target_island=1)
+                self.assertIn("program_2", resumed.islands[1])
+                self.assertIn("program_2", resumed.island_feature_maps[1].values())
+
+    def test_resume_without_saved_feature_maps(self):
+        metadata_path = os.path.join(self.checkpoint_path, "metadata.json")
+        with open(metadata_path) as metadata_file:
+            metadata = json.load(metadata_file)
+        del metadata["island_feature_maps"]
+        with open(metadata_path, "w") as metadata_file:
+            json.dump(metadata, metadata_file)
+
+        resumed = self.load_database(num_islands=1)
+        resumed.add(self.make_program(2), target_island=1)
+
+        self.assertEqual(len(resumed.island_feature_maps), 2)
+        self.assertEqual(resumed.island_feature_maps[0], {})
+        self.assertEqual(set(resumed.island_feature_maps[1].values()), {"program_2"})
+
+
+if __name__ == "__main__":
+    unittest.main()