Improve error messages for parse failures (#732)

Improve command output for cases like parsing helm values that contain
invalid values.

#731

flux_local/kustomize.py

@@ -127,7 +127,12 @@ async def objects(
         self, target_namespace: str | None = None
     ) -> list[dict[str, Any]]:
         """Run the kustomize command and return the result cluster objects as a list."""
-        return [doc async for doc in self._docs(target_namespace=target_namespace)]
+        try:
+            return [doc async for doc in self._docs(target_namespace=target_namespace)]
+        except yaml.YAMLError as err:
+            raise KustomizeException(
+                f"Unable to parse command output: {self._cmds}: {err}"
+            ) from err
 
     def skip_resources(self, kinds: list[str]) -> "Kustomize":
         """Skip resources kinds of the specified types."""

tests/test_kustomize.py

@@ -6,7 +6,7 @@
 from syrupy.assertion import SnapshotAssertion
 import yaml
 
-from flux_local import kustomize, exceptions, manifest
+from flux_local import kustomize, exceptions, manifest, command
 
 TESTDATA_DIR = Path("tests/testdata")
 
@@ -44,6 +44,28 @@ async def test_objects(path: Path, snapshot: SnapshotAssertion) -> None:
     assert result == snapshot
 
 
+INVALID_YAML = """
+---
+foo: !bar
+"""
+
+
+async def test_objects_failure() -> None:
+    """Test loading yaml documents."""
+
+    class FakeTask(command.Task):
+        async def run(self, stdin: bytes | None = None) -> bytes:
+            """Execute the task and return the result."""
+            return INVALID_YAML.encode()
+
+    cmd = kustomize.Kustomize([FakeTask()])
+    with pytest.raises(
+        exceptions.KustomizeException,
+        match=r"Unable to parse.*could not determine a constructor",
+    ):
+        await cmd.objects()
+
+
 @pytest.mark.parametrize(
     "path",
     [TESTDATA_DIR / "repo", (TESTDATA_DIR / "repo").absolute()],
@@ -80,8 +102,7 @@ async def test_validate_pass(path: Path) -> None:
 async def test_validate_fail(path: Path) -> None:
     """Test applying policies to validate resources."""
     cmd = kustomize.grep("kind=ConfigMap", path)
-    with pytest.raises(
-        exceptions.CommandException, match="fail: 1"):
+    with pytest.raises(exceptions.CommandException, match="fail: 1"):
         await cmd.validate(TESTDATA_DIR / "policies/fail.yaml")