fix(substitution_args.py): _resolve_args() not finding commands

[Amronos]

The below wasn't working for me; replacing the custom split logic in _resolve_args() with shlex seems to do the trick.

  <xacro:include filename="$(find some_package)/description/some.urdf.xacro" />

Error log:

Captured stderr output: error: <class 'xacro.substitution_args.SubstitutionException'>: Unknown substitution command [find some_package]. Valid commands are ['find', 'env', 'optenv', 'dirname', 'arg']

[rhaschke]

I cannot reproduce your issue. We do have a succeeding unit test for this:

xacro/test/test_xacro.py

Lines 570 to 573 in 1f24172

	def test_substitution_args_find(self):
	resolved = self.quick_xacro('''<a>$(find xacro)/test/test_xacro.py</a>''').firstChild.firstChild.data
	self.assertEqual(os.path.realpath(resolved), os.path.realpath(__file__))

Could you please clarify under which circumstances you get the error?

Your solution introduces another dependency, which I would like to avoid.

[Amronos]

I personally encountered it here.

The reason, though, may not be related to my code but rather to the fact that I am using Nix/NixOS with nix-ros-overlay. Perhaps something changed between Python versions?
I would therefore like to add @wentasah (the current maintainer of nix-ros-overlay) to the thread.

Also, shlex isn't an external dependency; it is part of the Python standard library.

[wentasah]

I've just run xacro tests under nix-ros-overlay and all of them seem to pass:

colcon test --event-handlers console_direct+
Starting >>> xacro   
UpdateCTestConfiguration  from :/home/wsh/src/github.com/ros/xacro/build/xacro/CTestConfiguration.ini
Parse Config file:/home/wsh/src/github.com/ros/xacro/build/xacro/CTestConfiguration.ini
   Site: steelpick
   Build name: (empty)
 Add coverage exclude regular expressions.
Create new tag: 20260316-1259 - Experimental
UpdateCTestConfiguration  from :/home/wsh/src/github.com/ros/xacro/build/xacro/CTestConfiguration.ini
Parse Config file:/home/wsh/src/github.com/ros/xacro/build/xacro/CTestConfiguration.ini
Test project /home/wsh/src/github.com/ros/xacro/build/xacro
Constructing a list of tests
Done constructing a list of tests
Updating test list for fixtures
Added 0 tests to meet fixture requirements
Checking test dependency graph...
Checking test dependency graph end
test 1
    Start 1: pytest

1: Test command: /nix/store/j0cxym3cn4nfqqvaw3zbx8mvyx5zgh4i-ros-env/bin/python3 "-u" "/nix/store/j0cxym3cn4nfqqvaw3zbx8mvyx5zgh4i-ros-env/share/ament_cmake_test/cmake/run_test.py" "/home/wsh/src/github.com/ros/xacro/build/xacro/test_results/xacro/pytest.xunit.xml" "--package-name" "xacro" "--output-file" "/home/wsh/src/github.com/ros/xacro/build/xacro/ament_cmake_pytest/pytest.txt" "--env" "PYTHONDONTWRITEBYTECODE=1" "AMENT_PREFIX_PATH=/home/wsh/src/github.com/ros/xacro/build/xacro/test/test_ament_index:/nix/store/j0cxym3cn4nfqqvaw3zbx8mvyx5zgh4i-ros-env" "--command" "/nix/store/j0cxym3cn4nfqqvaw3zbx8mvyx5zgh4i-ros-env/bin/python3" "-u" "-m" "pytest" "/home/wsh/src/github.com/ros/xacro/test/." "-o" "cache_dir=/home/wsh/src/github.com/ros/xacro/build/xacro/test/ament_cmake_pytest/pytest/.cache" "--junit-xml=/home/wsh/src/github.com/ros/xacro/build/xacro/test_results/xacro/pytest.xunit.xml" "--junit-prefix=xacro"
1: Working Directory: /home/wsh/src/github.com/ros/xacro/test
1: Test timeout computed to be: 60
1: -- run_test.py: extra environment variables:
1:  - AMENT_PREFIX_PATH=/home/wsh/src/github.com/ros/xacro/build/xacro/test/test_ament_index:/nix/store/j0cxym3cn4nfqqvaw3zbx8mvyx5zgh4i-ros-env
1:  - PYTHONDONTWRITEBYTECODE=1
1: -- run_test.py: invoking following command in '/home/wsh/src/github.com/ros/xacro/test':
1:  - /nix/store/j0cxym3cn4nfqqvaw3zbx8mvyx5zgh4i-ros-env/bin/python3 -u -m pytest /home/wsh/src/github.com/ros/xacro/test/. -o cache_dir=/home/wsh/src/github.com/ros/xacro/build/xacro/test/ament_cmake_pytest/pytest/.cache --junit-xml=/home/wsh/src/github.com/ros/xacro/build/xacro/test_results/xacro/pytest.xunit.xml --junit-prefix=xacro
1: ============================= test session starts ==============================
1: platform linux -- Python 3.13.7, pytest-8.4.1, pluggy-1.6.0
1: cachedir: build/xacro/test/ament_cmake_pytest/pytest/.cache
1: rootdir: /home/wsh/src/github.com/ros/xacro
1: configfile: pyproject.toml
1: plugins: colcon-core-0.20.1, cov-6.2.1, repeat-0.9.4, rerunfailures-15.1, launch_testing-3.9.6, launch_testing_ros-0.29.6, ament_copyright-0.20.3, ament_flake8-0.20.3, ament_lint-0.20.3, ament_mypy-0.20.3, ament_pep257-0.20.3, ament_xmllint-0.20.3, typeguard-4.4.4
1: collected 145 items
1: 
1: test_xacro.py .......................................................... [ 40%]
1: ........................................................................ [ 89%]
1: ...............                                                          [100%]
1: 
1: - generated xml file: /home/wsh/src/github.com/ros/xacro/build/xacro/test_results/xacro/pytest.xunit.xml -
1: ============================= 145 passed in 1.40s ==============================
1: -- run_test.py: return code 0    
1: -- run_test.py: verify result file '/home/wsh/src/github.com/ros/xacro/build/xacro/test_results/xacro/pytest.xunit.xml'
1/2 Test #1: pytest ...........................   Passed    2.13 sec
test 2                              
    Start 2: xacro_cmake

2: Test command: /home/wsh/src/github.com/ros/xacro/test/test-cmake.sh "/home/wsh/src/github.com/ros/xacro/test/test-xacro-cmake"
2: Working Directory: /home/wsh/src/github.com/ros/xacro/build/xacro/test
2: Test timeout computed to be: 10000000
2/2 Test #2: xacro_cmake ......................   Passed    3.22 sec

100% tests passed, 0 tests failed out of 2

Label Time Summary:
pytest    =   2.13 sec*proc (1 test)

Total Test time (real) =   5.45 sec
Finished <<< xacro [5.49s]

I checked that test_substitution_args_find test was executed in test_substitution_args_find and it was. Not sure, where is the problem.

[rhaschke]

@Amronos: could you create a minimal example, please.

[Amronos]

I wasn't able to create a minimal example, but I did find the below log upon appending --debug to my launch command:

<class 'xacro.substitution_args.SubstitutionException'>: Unknown substitution command [find\n      variobot_control]. Valid commands are ['find', 'env', 'optenv', 'dirname', 'arg'] Unknown substitution command [find\n      variobot_control]. Valid commands are ['find', 'env', 'optenv', 'dirname', 'arg']

Looks like a \n is inserted after the find command. This problem was simply solved by adding a .strip() after splits[0].

Should I make this change or should shlex be kept instead?

Sorry for needlessly pinging you @wentasah!

[rhaschke]

I prefer to have the strip(). The question remains, where the newline comes from. split() should actually split on any whitespace - including newlines.

[rhaschke]

Could you please check wheather splitting on any whitespace already resolves the problem too:

Suggested change

	splits = [s for s in a.split(' ') if s]
	splits = [s for s in a.split() if s]

[Amronos]

Thanks! That works. Fixed in d088535.

[rhaschke]

Thanks for reporting and iterating on this.