[Modular CLI]: wrong config path when installing mojo

[graelo]

Issue description

On macOS, after performing the initial install of the homebrew tap and adding the mut_xxxx token, my modular.cfg file is created in $XDG_CONFIG_HOME/modular/modular.cfg, as expected. Kudos for being good citizens and separating config from $XDG_DATA_HOME.

However, when running modular install mojo, I consistently have the following error

Error returned by `modular install mojo`

[notice] A new release of pip is available: 23.3.1 -> 24.0
[notice] To update, run: pip install --upgrade pip
Traceback (most recent call last):
  File "/Users/graelo/.local/share/modular/pkg/packages.modular.com_mojo/scripts/post-install/self-test.py", line 501, in <module>
    main()
  File "/Users/graelo/.local/share/modular/pkg/packages.modular.com_mojo/scripts/post-install/self-test.py", line 491, in main
    tester = Tester(
             ^^^^^^^
  File "/Users/graelo/.local/share/modular/pkg/packages.modular.com_mojo/scripts/post-install/self-test.py", line 87, in __init__
    mojo_python_library = config.get("mojo", "python_lib").rstrip(";")
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/[email protected]/3.11.7_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/configparser.py", line 797, in get
    d = self._unify_values(section, vars)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/[email protected]/3.11.7_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/configparser.py", line 1168, in _unify_values
    raise NoSectionError(section) from None
configparser.NoSectionError: No section: 'mojo'
modular: error: failed to run script
==========================
Failure Information:
        - Script: `PATH=/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin:/Users/graelo/gopath/bin:/Users/graelo/.cargo/bin:/Library/TeX/texbin:/opt/homebrew/opt/openjdk/bin PYTHONPATH=/Users/graelo/.local/share/modular/pkg/packages.modular.com_mojo/venv/lib/Users/graelo/.local/share/modular/pkg/packages.modular.com_mojo/venv/bin/python /Users/graelo/.local/share/modular/pkg/packages.modular.com_mojo/scripts/post-install/self-test.py --modular-home /Users/graelo/.local/share/modular --package-path /Users/graelo/.local/share/modular/pkg/packages.modular.com_mojo`
`       - Result: 1
        - Stderr:
Traceback (most recent call last):
  File "/Users/graelo/.local/share/modular/pkg/packages.modular.com_mojo/scripts/post-install/self-test.py", line 501, in <module>
    main()
  File "/Users/graelo/.local/share/modular/pkg/packages.modular.com_mojo/scripts/post-install/self-test.py", line 491, in main
    tester = Tester(
             ^^^^^^^
  File "/Users/graelo/.local/share/modular/pkg/packages.modular.com_mojo/scripts/post-install/self-test.py", line 87, in __init__
    mojo_python_library = config.get("mojo", "python_lib").rstrip(";")
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/[email protected]/3.11.7_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/configparser.py", line 797, in get
    d = self._unify_values(section, vars)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/[email protected]/3.11.7_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/configparser.py", line 1168, in _unify_values
    raise NoSectionError(section) from None
configparser.NoSectionError: No section: 'mojo'

Looking at the command launching self-test.py reveals the issue:

the $XDG_CONFIG_HOME should be used for --modular-home, but it is not:

self-test.py \
  --modular-home /Users/graelo/.local/share/modular \
  --package-path /Users/graelo/.local/share/modular/pkg/packages.modular.com_mojo

You can see that self-test.py is launched with the wrong path for --modular-home: it should be $XDG_CONFIG_HOME, meaning ~/.config/modular.

2 short-term workarounds:

• one ugly workaround: define the MODULAR_HOME env variable as ~/.config/modular. Installation then proceeds, but all the installation goes into the $XDG_CONFIG_HOME (~/.config), instead of $XDG_DATA_HOME. For those wondering, typically $XDG_CONFIG_HOME is config that can be tracked in git.

• one nicer workaround: create a symlink from $XDG_DATA_HOME/modular.cfg to $XDG_CONFIG_HOME/modular.cfg so that the install is performed in $XDG_DATA_HOME

Thanks in advance for fixing this in the next release!

Steps to reproduce

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• If applicable, add screenshots to help explain the problem.
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Version Info

- Provide Modular CLI version by pasting the output of `modular -v`


modular 0.4.1 (2d8afe15)

• What OS did you install modular CLI on ?

  Host Information
  ================

  Target Triple: aarch64-unknown-macosx
  CPU: apple-m1
  CPU Features: aes, crc, dotprod, fp-armv8, fp16fml, fullfp16, lse, neon, ras, rcpc, rdm, sha2, sha3