fix: Windows Path Handling and Normalize Cross-Platform Path Resolution in AgentLoader

Merge https://github.com/google/adk-python/pull/3609

Co-authored-by: George Weale <gweale@google.com>
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/3609 from p-kris10:fix/windows-cmd 8cb0310bd4450097a0a7714eaac6521b6a447442
PiperOrigin-RevId: 836395714

tests/unittests/agents/test_agent_config.py

@@ -12,14 +12,19 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import ntpath
+import os
 from pathlib import Path
+from textwrap import dedent
 from typing import Literal
 from typing import Type
+from unittest import mock
 
 from google.adk.agents import config_agent_utils
 from google.adk.agents.agent_config import AgentConfig
 from google.adk.agents.base_agent import BaseAgent
 from google.adk.agents.base_agent_config import BaseAgentConfig
+from google.adk.agents.common_configs import AgentRefConfig
 from google.adk.agents.llm_agent import LlmAgent
 from google.adk.agents.loop_agent import LoopAgent
 from google.adk.agents.parallel_agent import ParallelAgent
@@ -280,3 +285,91 @@ other_field: other value
       config.root.model_dump()
   )
   assert my_custom_config.other_field == "other value"
+
+
+@pytest.mark.parametrize(
+    ("config_rel_path", "child_rel_path", "child_name", "instruction"),
+    [
+        (
+            Path("main.yaml"),
+            Path("sub_agents/child.yaml"),
+            "child_agent",
+            "I am a child agent",
+        ),
+        (
+            Path("level1/level2/nested_main.yaml"),
+            Path("sub/nested_child.yaml"),
+            "nested_child",
+            "I am nested",
+        ),
+    ],
+)
+def test_resolve_agent_reference_resolves_relative_paths(
+    config_rel_path: Path,
+    child_rel_path: Path,
+    child_name: str,
+    instruction: str,
+    tmp_path: Path,
+):
+  """Verify resolve_agent_reference resolves relative sub-agent paths."""
+  config_file = tmp_path / config_rel_path
+  config_file.parent.mkdir(parents=True, exist_ok=True)
+
+  child_config_path = config_file.parent / child_rel_path
+  child_config_path.parent.mkdir(parents=True, exist_ok=True)
+  child_config_path.write_text(dedent(f"""
+          agent_class: LlmAgent
+          name: {child_name}
+          model: gemini-2.0-flash
+          instruction: {instruction}
+          """).lstrip())
+
+  config_file.write_text(dedent(f"""
+          agent_class: LlmAgent
+          name: main_agent
+          model: gemini-2.0-flash
+          instruction: I am the main agent
+          sub_agents:
+            - config_path: {child_rel_path.as_posix()}
+          """).lstrip())
+
+  ref_config = AgentRefConfig(config_path=child_rel_path.as_posix())
+  agent = config_agent_utils.resolve_agent_reference(
+      ref_config, str(config_file)
+  )
+
+  assert agent.name == child_name
+
+  config_dir = os.path.dirname(str(config_file.resolve()))
+  assert config_dir == str(config_file.parent.resolve())
+
+  expected_child_path = os.path.join(config_dir, *child_rel_path.parts)
+  assert os.path.exists(expected_child_path)
+
+
+def test_resolve_agent_reference_uses_windows_dirname():
+  """Ensure Windows-style config references resolve via os.path.dirname."""
+  ref_config = AgentRefConfig(config_path="sub\\child.yaml")
+  recorded: dict[str, str] = {}
+
+  def fake_from_config(path: str):
+    recorded["path"] = path
+    return "sentinel"
+
+  with (
+      mock.patch.object(
+          config_agent_utils,
+          "from_config",
+          autospec=True,
+          side_effect=fake_from_config,
+      ),
+      mock.patch.object(config_agent_utils.os, "path", ntpath),
+  ):
+    referencing = r"C:\workspace\agents\main.yaml"
+    result = config_agent_utils.resolve_agent_reference(ref_config, referencing)
+
+  expected_path = ntpath.join(
+      ntpath.dirname(referencing), ref_config.config_path
+  )
+  assert result == "sentinel"
+  assert recorded["path"] == expected_path

tests/unittests/cli/utils/test_agent_loader.py

@@ -12,12 +12,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import ntpath
 import os
 from pathlib import Path
+from pathlib import PureWindowsPath
+import re
 import sys
 import tempfile
 from textwrap import dedent
 
+from google.adk.cli.utils import agent_loader as agent_loader_module
 from google.adk.cli.utils.agent_loader import AgentLoader
 from pydantic import ValidationError
 import pytest
@@ -280,6 +284,43 @@ class TestAgentLoader:
       assert agent2 is not agent3
       assert agent1.agent_id != agent2.agent_id != agent3.agent_id
 
+  def test_error_messages_use_os_sep_consistently(self):
+    """Verify error messages use os.sep instead of hardcoded '/'."""
+    del self
+    with tempfile.TemporaryDirectory() as temp_dir:
+      loader = AgentLoader(temp_dir)
+      agent_name = "missing_agent"
+
+      expected_path = os.path.join(temp_dir, agent_name)
+
+      with pytest.raises(ValueError) as exc_info:
+        loader.load_agent(agent_name)
+
+      exc_info.match(re.escape(expected_path))
+      exc_info.match(re.escape(f"{agent_name}{os.sep}root_agent.yaml"))
+      exc_info.match(re.escape(f"<agents_dir>{os.sep}"))
+
+  def test_agent_loader_with_mocked_windows_path(self, monkeypatch):
+    """Mock Path() to simulate Windows behavior and catch regressions.
+
+    REGRESSION TEST: Fails with rstrip('/'), passes with str(Path()).
+    """
+    del self
+    windows_path = "C:\\Users\\dev\\agents\\"
+
+    with monkeypatch.context() as m:
+      m.setattr(
+          agent_loader_module,
+          "Path",
+          lambda path_str: PureWindowsPath(path_str),
+      )
+      loader = AgentLoader(windows_path)
+
+      expected = str(PureWindowsPath(windows_path))
+      assert loader.agents_dir == expected
+      assert not loader.agents_dir.endswith("\\")
+      assert not loader.agents_dir.endswith("/")
+
   def test_agent_not_found_error(self):
     """Test that appropriate error is raised when agent is not found."""
     with tempfile.TemporaryDirectory() as temp_dir: