debugging gnulib-tool.py

[Bruno Haible]

Hi,

In order to debug Simon's report
<https://lists.gnu.org/archive/html/bug-gnulib/2024-03/msg00152.html>,
I decided to use a GUI debugger, rather than the primitive print(...)-based
debugging.

* Choice: It seems that PyCharm, VSCode, Spyder, Eclipse with PyDev are the
  most prominent candidates.

  VSCode is "modern", but
    - the builds by Microsoft contain proprietary software,
    - you have to explicitly opt-out from telemetry collection if you want
      your privacy to be preserved,
    - last time I used it (two years ago), it had bugs related to caches,
      with the effect that syntax errors were shown that I already had
      corrected.

  So, I chose Eclipse with PyDev.

Eclipse has a long learning curve (2 weeks from the ground), therefore here
is how I configure it.

* Download and configuration:
  - Eclipse IDE from https://www.eclipse.org/downloads/packages/
    (either the build for Java or for C/C++ should work fine).
  - PyDev from https://www.pydev.org/download.html
    section "Install as Plugin".
    (Don't use LiClipse, since the license costs money.)
  - Follow https://www.pydev.org/manual_101_install.html,
    replacing http://www.pydev.org/updates
    with      https://www.pydev.org/updates
  - Once installed, restart the IDE.
  - Window > Preferences > PyDev > Interpreters > Python Interpreter:
    New > path: /usr/bin/python3

* Create a project:
  Let GNULIB_DIR be my gnulib checkout.
  - File > New > Project... > PyDev > PyDev Project. Call it 'gnulib'.
    Note that this is a project inside the Eclipse workspace, so far
    unrelated to the GNULIB_DIR.
  - Popup menu > New > Link to Existing Source
    Name: pygnulib
    Path: <GNULIB_DIR>/pygnulib

* Create a run configuration:
  - Run > Run Configurations... > Python Run
    Popup menu > New configuration
      Name: gnulib-tool.py
      Main > Project: gnulib
      Environment > Add
        Variable: PYTHONPATH
        Value: <GNULIB_DIR>
        (This is the same hack as in <GNULIB_DIR>/gnulib-tool.py.)
      Arguments > Program arguments: --help
  - Test it: Run this configuration.

* Create a debug configuration:
  - Run > Debug Configurations... > gnulib-tool.py
    Popup menu > Duplicate
  - In the duplicate, set
    Arguments > Working directory: /tmp/oath-toolkit/lib
    Arguments > Program arguments: --add-import

* Debug it:
  - Open GLImport.py.
  - On the left-hand border of this editor, do "Add breakpoint".
  - Run > Debug Configurations... > pick the duplicate. Press Debug.