Add front-end implementation for conda-standalone uninstall subcommand

[marcoesters]

Description

Uninstalling distributions for conda currently only has incomplete solutions with files and broken auto-run/initializer scripts left behind (see #642, #588, and #572). A clean uninstallation is currently not available without manually running a series of commands that are still not 100% safe - e.g., conda init --reverse --all will remove initialization of conda, no matter what installation it is pointed to.

conda-standalone is implementing an uninstallation subcommand (see conda/conda-standalone#112) to alleviate these issues. This PR implements the front-end implementation of the uninstallation options for the Windows uninstaller (see screenshot).

The conda-standalone feature needs to be merged and uploaded first before merging this PR.

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[marcoesters]

I think this can be reviewed already, even though we have to wait for a new conda-standalone before we can fully test it.

[jaimergp]

The Windows changes LGTM. It's a lot of NSIS code so I'm assuming this thing runs correctly and if there are edge cases, I guess we'll hear about it.

I'm curious about the uninstallation story for Linux and macOS, though. In principle, users can just run conda.exe constructor uninstall --prefix <install path, right? Is it really that simple? I think we should document this in any case, maybe a new page under the How-to section? WDYT?

[marcoesters]

The Windows changes LGTM. It's a lot of NSIS code so I'm assuming this thing runs correctly and if there are edge cases, I guess we'll hear about it.

I will re-run the CI when the new conda-standalone is published. Those tests have helped find issues in both the constructor and conda-standalone implementation. Edge cases are bound to come up. which is why I made this an opt-in feature via uninstall_with_conda_exe.

I'm curious about the uninstallation story for Linux and macOS, though. In principle, users can just run conda.exe constructor uninstall --prefix <install path, right? Is it really that simple? I think we should document this in any case, maybe a new page under the How-to section? WDYT?

It really is that simple. A new page in the how-to section sounds interesting. We could use this to set a standard on how these uninstallers ought to be implemented. We are implicitly doing this with the Windows front-end already.

[jaimergp]

It really is that simple. A new page in the how-to section sounds interesting. We could use this to set a standard on how these uninstallers ought to be implemented. We are implicitly doing this with the Windows front-end already.

Let's write this page here and then I'll approve!

[marcoesters]

@jaimergp, I had to make a change in the uninstallation behavior. The issue was that there were some .conda_trash files left in a subdirectory when running on the CI and my function didn't account for it.

That gave me two choices: implement a recursive search in NSIS (no) or try and delete the directory the way we do it with the old uninstaller method. I opted for the latter.