Command "firebase emulators:export ." deleted all my files without any warning

[gitslav]

[REQUIRED] Environment info

firebase-tools: 9.19.0

Platform: macOS

[REQUIRED] Test case

[REQUIRED] Steps to reproduce

1. In directory A create a symlink B to directory C (imagine all our projects are located here)
2. cd B
3. cd D (one of our projects)
4. run "firebase emulators:export ."

[REQUIRED] Expected behavior

1. Important project files are still existing in current folder.
2. Set of entity export files is created in current folder.

[REQUIRED] Actual behavior

1. All important project files are deleted
2. Set of entity export files are not created in current folder
3. Error "Export request failed, see emulator logs for more information." is shown

Edit:
After trying to reproduce the issue I found that I used a symlink while navigating to the final directory.

firebase-tools/src/emulator/controller.ts

Line 749 in 3d5b8cd

const exportAbsPath = path.resolve(exportPath);

This does not resolve/respect symlinks and is probably where the issue starts from.

[abeisgoat]

Hmm, thanks for raising this, the CLI should really prompt you if you're attempting to export to a directory which already has files in it. We'll put this as a feature request.

[gitslav]

@abeisgoat the CLI does prompt you if the path does not contain a symbolic link.
If it does contain a symbolic link the use of "path.resolve" function (shown above) breaks the flow and leads to a bug where the files are deleted.
A proper way to implement this should probably be by using "fs.realpath" function as it is resolving properly ., .. and symbolic links.

[DiegoGonzalezCruz]

OMG I can't believe I'm not the only person...

[gitslav]

It's a really nasty bug. Not sure why @abeisgoat added a feature request label 😃

[yuchenshi]

Just to add a bit of context, we've fixed the most common and dangerous case of wiping your project directory in #4127 so please update to the latest CLI version. However, the detection is imperfect that it doesn't handle symlinks, which we can tackle next (as @gitslav suggested).

There's also a possibility for one to specify some other directory that is not within the project but contains other files, which we're still trying to figure out the best behavior. Prompting is a good idea, but it may break many test scripts and use cases that overwrites previous exports. Besides, it doesn't really work with --export-on-exit when the process is exiting and cannot wait on interactive input. Ideas welcome here.

[Elias070]

Lost half of all progress because of this bug... please fix, or atleast add warning in documentation

[colerogers]

Closing this out since we have #3092 as the proper place for discussion