fix: Preserve existing config.toml entries that are not managed by this tool

colcon_ros_cargo/task/ament_cargo/build.py

@@ -110,10 +110,23 @@ def write_cargo_config_toml(package_paths):
     :param package_paths: A mapping of package names to paths
     """
     patches = {pkg: {'path': str(path)} for pkg, path in package_paths.items()}
-    content = {'patch': {'crates-io': patches}}
+
     config_dir = Path.cwd() / '.cargo'
     config_dir.mkdir(exist_ok=True)
     cargo_config_toml_out = config_dir / 'config.toml'
+
+    if cargo_config_toml_out.exists():
+        with cargo_config_toml_out.open('r') as toml_file:
+            content = toml.load(toml_file)
+    else:
+        content = {}
+
+    if 'patch' not in content:
+        content['patch'] = {}
+
+    # remove old entries
+    content['patch']['crates-io'] = patches
+
     with cargo_config_toml_out.open('w') as toml_file:
         toml.dump(content, toml_file)
 

test/test_cargo_config_toml.py

 def test_flake8(): 
 def test_flake8(): 
@@ -0,0 +1,112 @@
+import pytest
+from pathlib import Path
+import toml
+import os
+
+from colcon_ros_cargo.task.ament_cargo.build import write_cargo_config_toml
+
+
+@pytest.fixture
+def temp_workspace(tmp_path):
+    """Create a temporary workspace directory."""
+    original_cwd = os.getcwd()
+    os.chdir(tmp_path)
+    yield tmp_path
+    os.chdir(original_cwd)
+
+
+def test_write_cargo_config_toml_creates_new_file(temp_workspace):
+    """Test that config.toml is created when it doesn't exist."""
+    package_paths = {
+        "my_package": Path("/path/to/my_package"),
+        "other_package": Path("/path/to/other_package"),
+    }
+
+    write_cargo_config_toml(package_paths)
+
+    config_file = temp_workspace / ".cargo" / "config.toml"
+    assert config_file.exists()
+
+    with config_file.open("r") as f:
+        content = toml.load(f)
+
+    assert "patch" in content
+    assert "crates-io" in content["patch"]
+    assert content["patch"]["crates-io"]["my_package"] == {
+        "path": "/path/to/my_package"
+    }
+    assert content["patch"]["crates-io"]["other_package"] == {
+        "path": "/path/to/other_package"
+    }
+
+
+def test_write_cargo_config_toml_merges_entries(temp_workspace):
+    """Test that the it merges its changes and preserves existing config."""
+    config_dir = temp_workspace / ".cargo"
+    config_dir.mkdir(exist_ok=True)
+    config_file = config_dir / "config.toml"
+
+    existing_content = {
+        "build": {
+            "target": "x86_64-unknown-linux-gnu",
+            "jobs": 4,
+        },
+        "patch": {
+            "crates-io": {
+                "existing_package": {"path": "/existing/path"},
+            }
+        },
+    }
+
+    with config_file.open("w") as f:
+        toml.dump(existing_content, f)
+
+    package_paths = {
+        "new_package": Path("/path/to/new_package"),
+    }
+
+    write_cargo_config_toml(package_paths)
+
+    with config_file.open("r") as f:
+        content = toml.load(f)
+
+    # Existing config is preserved
+    assert content["build"]["target"] == "x86_64-unknown-linux-gnu"
+    assert content["build"]["jobs"] == 4
+
+    # Old crates-io patch is removed
+    assert "existing_package" not in content["patch"]["crates-io"]
+
+    # New crates-io patch is present
+    assert content["patch"]["crates-io"]["new_package"] == {
+        "path": "/path/to/new_package"
+    }
+
+
+def test_write_cargo_config_toml_updates_existing_patch(temp_workspace):
+    """Test that updating an existing patch overwrites it."""
+    config_dir = temp_workspace / ".cargo"
+    config_dir.mkdir(exist_ok=True)
+    config_file = config_dir / "config.toml"
+
+    existing_content = {
+        "patch": {
+            "crates-io": {
+                "my_package": {"path": "/old/path"},
+            }
+        }
+    }
+
+    with config_file.open("w") as f:
+        toml.dump(existing_content, f)
+
+    package_paths = {
+        "my_package": Path("/new/path"),
+    }
+
+    write_cargo_config_toml(package_paths)
+
+    with config_file.open("r") as f:
+        content = toml.load(f)
+
+    assert content["patch"]["crates-io"]["my_package"] == {"path": "/new/path"}