Enhance Bazel Scan-Headers Error Messages For RobotPy

When working with RobotPy and Bazel, encountering errors during the scan-headers process can be a common challenge. The current error messages often lack sufficient context, leaving developers puzzled about the necessary steps to resolve the issue. This article delves into the problem, proposes a solution, explores alternatives, and provides a detailed explanation to improve the user experience.

The Problem: Lack of Context in Scan-Headers Error Messages

Currently, when the scan-headers process fails in Bazel, it outputs lines that are meant to be added to the pyproject.toml file. However, the error message provides absolutely no context or explanation regarding the purpose or meaning of these lines. If a developer is already familiar with the README-RobotPy.md file, they might understand what to do. But for those who aren't, the error message can be extremely confusing and frustrating.

Understanding the Impact:

• Increased Learning Curve: New users face a steeper learning curve as they need to consult external documentation to understand the error messages.
• Wasted Time: Developers spend valuable time searching for solutions instead of focusing on development.
• Frustration: Lack of clear guidance can lead to frustration and a negative experience with the toolchain.

Let's illustrate this with an example error message:

exec ${PAGER:-/usr/bin/less} "$0" || exit 1
Executing tests from //wpimath:robotpy-wpimath-scan-headers
-----------------------------------------------------------------------------
# wpi
units-usc = "wpi/units-usc.hpp"
units = "wpi/units.hpp"

Traceback (most recent call last):
  File "/private/var/tmp/.../execroot/__main__/bazel-out/darwin_arm64-fastbuild/bin/wpimath/robotpy-wpimath-scan-headers.runfiles/__main__/shared/bazel/rules/robotpy/wrapper.py", line 37, in main
    tool_main()
  File "/private/var/tmp/.../execroot/__main__/bazel-out/darwin_arm64-fastbuild/bin/wpimath/robotpy-wpimath-scan-headers.runfiles/allwpilib_pip_deps_semiwrap/site-packages/semiwrap/tool/__main__.py", line 38, in main
    sys.exit(retval)
SystemExit: 1

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/private/var/tmp/.../execroot/__main__/bazel-out/darwin_arm64-fastbuild/bin/wpimath/robotpy-wpimath-scan-headers.runfiles/__main__/wpimath/_robotpy-wpimath-scan-headers_stage2_bootstrap.py", line 499, in <module>
    main()
  File "/private/var/tmp/.../execroot/__main__/bazel-out/darwin_arm64-fastbuild/bin/wpimath/robotpy-wpimath-scan-headers.runfiles/__main__/wpimath/_robotpy-wpimath-scan-headers_stage2_bootstrap.py", line 493, in main
    _run_py_path(main_filename, args=sys.argv[1:])
...
  File "/private/var/tmp/.../execroot/__main__/bazel-out/darwin_arm64-fastbuild/bin/wpimath/robotpy-wpimath-scan-headers.runfiles/__main__/shared/bazel/rules/robotpy/wrapper.py", line 55, in <module>
    main()
  File "/private/var/tmp/.../execroot/__main__/bazel-out/darwin_arm64-fastbuild/bin/wpimath/robotpy-wpimath-scan-headers.runfiles/__main__/shared/bazel/rules/robotpy/wrapper.py", line 40, in main
    raise Exception(
Exception: ('sys.exit() explicitly called with a non-zero error code', SystemExit(1))

The core issue is the lack of clarity around the initial lines:

# wpi
units-usc = "wpi/units-usc.hpp"
units = "wpi/units.hpp"

Without prior knowledge, it's difficult to understand what these lines represent or where they should be added. This leads us to the proposed solution.

Proposed Solution: Enhanced Error Messages

The ideal solution is to provide more context within the error message itself. This could involve:

• Adding a brief explanation: Include a sentence or two explaining that the lines are intended to be added to the pyproject.toml file.
• Describing the purpose of the lines: Explain that these lines help the scan-headers tool locate the necessary header files.
• Providing a link to the relevant documentation: Include a direct link to the README-RobotPy.md file or a specific section within it.

Example of an Enhanced Error Message:

Error: The following entries are required in your `pyproject.toml` file to help the scan-headers tool locate the necessary header files. Please add these to the `[tool.semiwrap.includes]` section:

# wpi
units-usc = "wpi/units-usc.hpp"
units = "wpi/units.hpp"

For more information, see: [README-RobotPy.md](link-to-readme)

Traceback (most recent call last): ...

Benefits of the Enhanced Error Message:

• Improved User Experience: Developers can quickly understand the issue and take corrective action.
• Reduced Learning Curve: New users are guided towards the solution without needing to search for external documentation.
• Increased Efficiency: Developers spend less time troubleshooting and more time developing.

Alternatives Considered

One alternative is to rely on developers reading the README-RobotPy.md file. While this works to some extent, it's not an ideal solution for several reasons:

• Not Discoverable: Developers might not know that the README-RobotPy.md file contains the necessary information.
• Inconvenient: Requiring developers to consult external documentation for every error message is inconvenient and time-consuming.
• Not Scalable: As the project grows, relying on developers to read specific documentation becomes less sustainable.

Another alternative could be to add references in other .md files, such as README-Bazel.md. However, this approach might not be as effective as directly embedding the information in the error message.

Detailed Explanation of the Solution

The proposed solution focuses on enhancing the error messages generated by the scan-headers tool. This involves modifying the tool's code to include more informative messages when errors occur.

Implementation Steps:

1. Locate the Error Message Generation Code: Identify the specific code section in the scan-headers tool that generates the error message.
2. Modify the Error Message: Update the error message to include the following information:
   • A clear statement that the provided lines need to be added to the pyproject.toml file.
   • An explanation of the purpose of these lines (e.g., to help the tool locate header files).
   • A link to the relevant section in the README-RobotPy.md file.
3. Test the Changes: Thoroughly test the modified tool to ensure that the enhanced error messages are displayed correctly and provide accurate information.

Example Code Snippet (Illustrative):

# Original error message
print("# wpi\nunits-usc = \"wpi/units-usc.hpp\"\nunits = \"wpi/units.hpp\"")

# Enhanced error message
print("""Error: The following entries are required in your `pyproject.toml` file to help the scan-headers tool locate the necessary header files. Please add these to the `[tool.semiwrap.includes]` section:

# wpi
units-usc = \"wpi/units-usc.hpp\"\nunits = \"wpi/units.hpp\"

For more information, see: [README-RobotPy.md](link-to-readme)""")

Benefits of this Approach:

• Direct Guidance: The error message directly guides the developer to the solution.
• Contextual Information: The message provides context about the purpose of the required entries.
• Easy Access to Documentation: The link to the README-RobotPy.md file provides easy access to more detailed information.

Conclusion

Improving the Bazel scan-headers error messages is crucial for enhancing the RobotPy development experience. By providing more context and guidance within the error messages, we can reduce the learning curve, save developers time, and increase overall efficiency. The proposed solution involves modifying the tool's code to include more informative messages, which can significantly improve the user experience. While alternatives exist, directly embedding the necessary information in the error message is the most effective approach.

For more information on RobotPy and Bazel integration, you can refer to the official RobotPy documentation.