Compilation Error: Duplicate action writing to `desktop_resources_folder_cmd.bat`

Description:

While compiling a project using the following command:

bazel build -c opt --define MEDIAPIPE_DISABLE_GPU=1 --action_env PYTHON_BIN_PATH="C:\\Users\\hans9\\AppData\\Local\\Programs\\Python\\Python310\\python.exe" -s //magritte/examples/desktop:desktop_resources_folder --experimental_repo_remote_exec --copt -DBOOST_ERROR_CODE_HEADER_ONLY --copt -DMESA_EGL_NO_X11_HEADERS --copt -DEGL_NO_X11

I encountered an error indicating a conflict with the file desktop_resources_folder_cmd.bat. The exact error message is:

ERROR: C:/users/hans9/onedrive/documents/hans/travail/inmersiv/projet_apprentissage/mediapipe/prise_en_main_c++/magritte/magritte/examples/desktop/BUILD:92:26: for magritte/examples/desktop/desktop_resources_folder_cmd.bat, previous action: action 'Writing script magritte/examples/desktop/desktop_resources_folder_cmd.bat', attempted action: action 'Writing script magritte/examples/desktop/desktop_resources_folder_cmd.bat'

Environment:

OS: Windows 11

Additional Information:

The build process seems to be attempting to write to desktop_resources_folder_cmd.bat multiple times, which is causing the conflict.
I've verified that the logic generating the .bat filename is unique to its context.
The error might be related to some rules or macros generating the same file, but I've been unable to identify the root cause.

I would appreciate any insights or potential fixes for this issue. Let me know if any additional information is required. Thanks in advance for your support.

Best regards,

I continued to investigate the problem and found the root cause, which occurs only on Windows systems. It is produced by the following code, originating from the file magritte_bzl.src:

# Copies a file to another file. If the destination directory does not exist
# it will be created. (Windows version)
def _copy_action_windows(ctx, input_file, output_file):
    bat = ctx.actions.declare_file(ctx.label.name + "_cmd.bat")
    # ... rest of the code

# Implementation function for rule below.
def _magritte_resources_folder_impl(ctx):
    # ... rest of the code
    for file in ctx.files.runtime_data:
        # ...
        if ctx.attr.is_windows:
            _copy_action_windows(ctx, file, output_file)

The error was occurring due to multiple actions trying to write to the same .bat file (bat = ctx.actions.declare_file(ctx.label.name + "_cmd.bat")) within the loop of def _magritte_resources_folder_impl(ctx). This was causing a conflict in the build process with Bazel, as it expects actions to have distinct outputs.

I've identified two solutions to resolve this problem and created two separate pull requests for them:

Solution 1: Direct Command Execution (Pull Request #18 )

Instead of writing to a .bat file, you can execute the necessary commands directly using cmd.exe. This solution removes the shared .bat file, allowing actions to be executed independently without conflict.

cmd_part1 = "(if not exist \"%s\" mkdir \"%s\")" % (destination_folder, destination_folder)
cmd_part2 = " && @copy /Y \"%s\" \"%s\"" % (file_to_copy, destination_folder)
cmd = cmd_part1 + cmd_part2

ctx.actions.run(
    inputs=[input_file],
    outputs=[output_file],
    executable="cmd.exe",
    arguments=["/C", cmd],
    use_default_shell_env=True,
)

Solution 2: Unique `.bat` Filename Using a Hash (Pull Request #19 )

You can modify the .bat filename to include a hash of the source path. By creating a unique filename for each action, this solution ensures that actions can be executed concurrently without any conflicting writes to the same file.

bat = ctx.actions.declare_file("%s-%s-cmd.bat" % (ctx.label.name, hash(src.path)))

Either solution should resolve the conflict and allow the Bazel build to proceed smoothly. Feel free to review the pull requests for more details.

Best regards,

google / magritte