Remove main file if empty during hex creation

[microbit-robert]

This creates a "clean" MicroPython hex. When the REPL is launched it already includes "from microbit import *".

[github-actions]

Preview build will be at
https://review-python-editor-v3.microbit.org/empty-main-file/

[microbit-robert]

Needs moving, otherwise the first save will include an empty main.py (which is then removed), and subsequent saves will not (unless code is added by the user).

[microbit-matt-hillsdon]

Please can we double check that we don't read main.py from the fs directly anywhere else?

[microbit-robert]

Please can we double check that we don't read main.py from the fs directly anywhere else?

We read it using FileSystem read, but not using MicropythonFsHex read/readBytes. So this looks safe to me.

Hmm did just create an error reloading a hex file though. Moving back to draft to investigate.

Update: We can't load a hex file that doesn't have a main.py. The same is true of a blank hex you can create from the V2 editor. I think we should fix as we're adding the ability to create such hex files in this PR.

[microbit-robert]

The V2 editor also fails to load hex files without python code:

Error occurs during call to importFilesFromHex in importFilesFromUniversalHex.

[microbit-robert]

This change also allows the user to create an additional file with content. If main.py is empty, the saved hex when re-imported will remove main.py from the project in the editor. Which leads to errors when saving the main Python file: unexpected-error-description Please try again or raise a support request