Added admoniton for a possible error fix

[giorgio-pasini]

While following the tutorial I got a Permission Error and didn't know how to proceed.

I've tried adding a folder the system was looking for and then the process continued smoothly. I thought that adding this admonition to the tutorial may help others in case this happens to them as well.

I added an admonition to let people know a possible solution to a possible problem encountered after the "briefcase build android" command.

Personally at first I found myself lost and I was even looking for other python-to-android builders and came back just because I've not found any that convinced me.
Adding that hint may help others not lose their time by doing that.

PR Checklist:

• All new features have been tested: the briefcase build android command worked and actually filled the folder. Now I have another problem with "briefcase runandroid", but I don't think it's correlated (the folder I manually created has been correctly filled by the "briefcase build android" command)
• [x ] All new features have been documented
• [ x] I have read the CONTRIBUTING.md file
• [x ] I will abide by the code of conduct

[rmartin16]

Hello @giorgio-pasini, would you be able to upload the Briefcase log file for this error? I'm curious if there's anything we can do to prevent this altogether.

[rmartin16]

One compelling reason I found for this error is a background process acquired a handle for the cmdline-tools directory or a file/directory within it; for instance, a Windows file indexer or maybe an antivirus scanner.

I could replicate the error using open() on a file in one Python interpreter and trying to call os.rename() for its directory in another. A mitigation might be automatically retry....

[giorgio-pasini]

Hello Russell,
I'll try to replicate the error from the very beginning cleaning up all the files.
I'll update you with what comes up.

Meanwhile, thanks for the kind and swift response!

[mhsmith]

@giorgio-pasini: Please check the logs directory of your project, and if you can find the log that corresponds to this error, upload it to the issue.

If the error was caused by what @rmartin16 thinks, I don't see how creating the directory manually would make any difference. Did you try running the same Briefcase command again before creating the directory? If so, did you get the same error, or a different one?

In any case, let's not clutter the documentation with workarounds for bugs that we can fix properly.

[freakboy3742]

I'm going to close this PR, on the basis that we'd prefer to fix the underlying problem than document our way around the problem. There's an open issue on Briefcase to track that problem.