python · zooba · Jun 9, 2025 · Jun 9, 2025 · Jun 9, 2025
diff --git a/src/manage/install_command.py b/src/manage/install_command.py
@@ -534,6 +534,26 @@
     LOGGER.verbose("Install complete")
 
 
+def _merge_existing_index(versions, index_json):
+    try:
+        with open(index_json, "r", encoding="utf-8") as f:
+            existing_index = json.load(f)
+        list(existing_index["versions"])
+    except FileNotFoundError:
+        pass
+    except (json.JSONDecodeError, KeyError, ValueError):
+        LOGGER.warn("Existing index file appeared invalid and was overwritten.")
+        LOGGER.debug("TRACEBACK", exc_info=True)
+    else:
+        LOGGER.debug("Merging into existing %s", index_json)
+        current = {i["url"].casefold() for i in versions}
+        added = []
+        for install in existing_index["versions"]:
+            if install.get("url", "").casefold() not in current:
+                LOGGER.debug("Merging %s", install.get("url", "<unspecified>"))
+                versions.append(install)
+
+
 def _fatal_install_error(cmd, ex):
     logfile = cmd.get_log_file()
     if logfile:
@@ -753,6 +773,7 @@
             return _fatal_install_error(cmd, ex)
 
         if cmd.download:
+            _merge_existing_index(download_index["versions"], cmd.download / "index.json")
             with open(cmd.download / "index.json", "w", encoding="utf-8") as f:
                 json.dump(download_index, f, indent=2, default=str)
             LOGGER.info("Offline index has been generated at !Y!%s!W!.", cmd.download)

diff --git a/tests/test_install_command.py b/tests/test_install_command.py
@@ -1,3 +1,4 @@
+import json
 import os
 import pytest
 import secrets
@@ -131,3 +132,60 @@ def get_installs(self):
     assert_log(
         assert_log.skip_until(".*Global shortcuts directory is not on PATH")
     )
+
+
+def test_merge_existing_index(tmp_path):
+    # This function is for multiple downloaded index.jsons, so it merges based
+    # on the url property, which should usually be a local file.
+    existing = tmp_path / "index.json"
+    with open(existing, "w", encoding="utf-8") as f:
+        json.dump({"versions": [
+            {"id": "test-1", "url": "test-file-1.zip"},
+            {"id": "test-2", "url": "test-file-2.zip"},
+            {"id": "test-3", "url": "test-file-3.zip"},
+        ]}, f)
+
+    new = [
+        # Ensure new versions appear first
+        {"id": "test-4", "url": "test-file-4.zip"},
+        # Ensure matching ID doesn't result in overwrite
+        {"id": "test-1", "url": "test-file-1b.zip"},
+        # Ensure matching URL excludes original entry
+        {"id": "test-2b", "url": "test-file-2.zip"},
+    ]
+
+    IC._merge_existing_index(new, existing)
+
+    assert new == [
+        {"id": "test-4", "url": "test-file-4.zip"},
+        {"id": "test-1", "url": "test-file-1b.zip"},
+        {"id": "test-2b", "url": "test-file-2.zip"},
+        {"id": "test-1", "url": "test-file-1.zip"},
+        {"id": "test-3", "url": "test-file-3.zip"},
+    ]
+
+
+def test_merge_existing_index_not_found(tmp_path):
+    existing = tmp_path / "index.json"
+    try:
+        existing.unlink()
+    except FileNotFoundError:
+        pass
+
+    # Expect no failure and no change
+    new = [1, 2, 3]
+    IC._merge_existing_index(new, existing)
+    assert new == [1, 2, 3]
+
+
+def test_merge_existing_index_not_valid(tmp_path):
+    existing = tmp_path / "index.json"
+    with open(existing, "w", encoding="utf-8") as f:
+        print("It's not a list of installs", file=f)
+        print("But more importantly,", file=f)
+        print("it's not valid JSON!", file=f)
+
+    # Expect no failure and no change
+    new = [1, 2, 3]
+    IC._merge_existing_index(new, existing)
+    assert new == [1, 2, 3]