move multiple-preserves check to config validation

src/btrfs2s3/_internal/commands/update.py

@@ -378,16 +378,6 @@ def command(*, console: Console, args: argparse.Namespace) -> int:
     s3_endpoint = s3_remote.get("endpoint", {})
 
     sources = config["sources"]
-    assert (  # noqa: S101
-        len(
-            {
-                upload["preserve"]
-                for source in sources
-                for upload in source["upload_to_remotes"]
-            }
-        )
-        == 1
-    )
     assert (  # noqa: S101
         len(
             {

src/btrfs2s3/_internal/config.py

@@ -198,9 +198,17 @@ def load_from_path(path: str | PathLike[str]) -> Config:
         msg = "multiple remotes not supported in this release"
         raise InvalidConfigError(msg)
 
+    all_sources = config["sources"]
+
     # https://github.com/sbrudenell/btrfs2s3/issues/81
-    if len({source["snapshots"] for source in config["sources"]}) > 1:
+    if len({source["snapshots"] for source in all_sources}) > 1:
         msg = "multiple snapshot locations not supported in this release"
         raise InvalidConfigError(msg)
 
+    all_uploads = [up for src in all_sources for up in src["upload_to_remotes"]]
+
+    if len({upload["preserve"] for upload in all_uploads}) > 1:
+        msg = "multiple preserve configurations not supported in this release"
+        raise InvalidConfigError(msg)
+
     return config

tests/config_test.py

@@ -267,3 +267,26 @@ def test_no_multiple_snapshot_locations(path: Path) -> None:
     """)
     with pytest.raises(InvalidConfigError):
         load_from_path(path)
+
+
+def test_no_multiple_preserves(path: Path) -> None:
+    path.write_text("""
+        timezone: a
+        sources:
+        - path: b
+          snapshots: c
+          upload_to_remotes:
+          - id: aws
+            preserve: 1y 1m
+        - path: x
+          snapshots: c
+          upload_to_remotes:
+          - id: aws
+            preserve: 1y
+        remotes:
+        - id: aws
+          s3:
+            bucket: d
+    """)
+    with pytest.raises(InvalidConfigError):
+        load_from_path(path)