support nodefaults in environment.yml specs

conda_lock/src_parser/environment_yaml.py

@@ -114,6 +114,11 @@ def parse_environment_file(
 
     env_yaml_data = yaml.safe_load(content)
     channels: List[str] = env_yaml_data.get("channels", [])
+    try:
+        # conda-lock will use `--override-channels` so nodefaults is redundant.
+        channels.remove("nodefaults")
+    except ValueError:
+        pass
 
     # These extension fields are nonstandard
     category: str = env_yaml_data.get("category") or "main"

tests/test-env-nodefaults/environment.yml

@@ -0,0 +1,5 @@
+channels:
+  - nodefaults
+  - conda-forge
+dependencies:
+  - python <3.11

tests/test_conda_lock.py

@@ -138,6 +138,11 @@ def filter_conda_environment(tmp_path: Path):
     return x
 
 
+@pytest.fixture
+def nodefaults_environment(tmp_path: Path):
+    return clone_test_dir("test-env-nodefaults", tmp_path).joinpath("environment.yml")
+
+
 @pytest.fixture
 def pip_environment(tmp_path: Path):
     return clone_test_dir("test-pypi-resolve", tmp_path).joinpath("environment.yml")
@@ -400,6 +405,11 @@ def test_parse_environment_file_with_pip(pip_environment: Path):
         ]
 
 
+def test_parse_env_file_with_no_defaults(nodefaults_environment: Path):
+    res = parse_environment_file(nodefaults_environment, DEFAULT_PLATFORMS)
+    assert res.channels == [Channel.from_string("conda-forge")]
+
+
 def test_parse_env_file_with_filters_no_args(filter_conda_environment: Path):
     platforms = parse_platforms_from_env_file(filter_conda_environment)
     res = parse_environment_file(filter_conda_environment, platforms)