fix: clean up config.py unused imports, null-YAML safety, and add non-default roundtrip test

src/autossh_mgr/config.py

@@ -1,7 +1,6 @@
 import os
-from dataclasses import dataclass, asdict, field
+from dataclasses import dataclass, asdict, fields as dc_fields
 from pathlib import Path
-from typing import Optional
 
 import click
 import yaml
@@ -28,9 +27,11 @@ class TunnelConfig:
     ssh_options: str = ""
 
 
-_DEFAULTS = TunnelConfig(
-    name="", host="", user="", local_port=0, remote_port=0
-)
+_OPTIONAL_DEFAULTS = {
+    f.name: f.default
+    for f in dc_fields(TunnelConfig)
+    if f.name in ("port", "identity_file", "local_host", "remote_host", "ssh_options")
+}
 
 
 def ensure_dirs(config_dir: Path) -> None:
@@ -47,7 +48,7 @@ def load_tunnels(config_dir: Path) -> list[TunnelConfig]:
     if not tunnels_file.exists():
         return []
     data = yaml.safe_load(tunnels_file.read_text()) or {}
-    return [TunnelConfig(**entry) for entry in data.get("tunnels", [])]
+    return [TunnelConfig(**entry) for entry in (data.get("tunnels") or [])]
 
 
 def save_tunnels(config_dir: Path, tunnels: list[TunnelConfig]) -> None:
@@ -55,8 +56,8 @@ def save_tunnels(config_dir: Path, tunnels: list[TunnelConfig]) -> None:
     for t in tunnels:
         d = asdict(t)
         # Omit optional fields that are at their default values
-        for key in ("port", "identity_file", "local_host", "remote_host", "ssh_options"):
-            if d[key] == getattr(_DEFAULTS, key):
+        for key, default in _OPTIONAL_DEFAULTS.items():
+            if d[key] == default:
                 del d[key]
         rows.append(d)
     tmp = config_dir / "tunnels.yaml.tmp"

tests/unit/test_config.py

@@ -2,7 +2,7 @@ import pytest
 import click
 from autossh_mgr.config import (
     TunnelConfig, ensure_dirs, load_tunnels, save_tunnels, get_tunnel
-)
+)  # TunnelConfig kept for test_save_preserves_non_default_values
 
 
 def test_ensure_dirs_creates_structure(tmp_path):
@@ -59,3 +59,22 @@ def test_get_config_dir_env_override(monkeypatch, tmp_path):
     monkeypatch.setenv("AUTOSSH_MGR_CONFIG_DIR", str(tmp_path))
     from autossh_mgr.config import get_config_dir
     assert get_config_dir() == tmp_path
+
+
+def test_save_preserves_non_default_values(config_dir):
+    tunnel = TunnelConfig(
+        name="custom", host="h.com", user="u",
+        local_port=80, remote_port=8080,
+        port=2222,
+        identity_file="~/.ssh/custom_key",
+        local_host="0.0.0.0",
+        remote_host="127.0.0.1",
+        ssh_options="-v",
+    )
+    save_tunnels(config_dir, [tunnel])
+    loaded = load_tunnels(config_dir)[0]
+    assert loaded.port == 2222
+    assert loaded.identity_file == "~/.ssh/custom_key"
+    assert loaded.local_host == "0.0.0.0"
+    assert loaded.remote_host == "127.0.0.1"
+    assert loaded.ssh_options == "-v"