[azure-cli-persistence] extensions folder exists but is not a symlink

[stuartleeks]

This error was encountered on a project

In OnCreate script
Permissions of '/dc/azure' are OK!
cliextensions folder found in old .azure folder
cliextensions folder ('/home/vscode/.azure/cliextensions') already exists in but is not a symlink

After some investigation, @cecheta discovered the repro steps:

• build a dev container with azure-cli-persistence
• manually install an az CLI extension
• update the azure-cli feature to install an extension
• rebuild the dev container

At this point, the manually installed extension causes the cliextensions folder to exist in the persistence volume location.
And the extension installed via the azure-cli feature causes the cliextensions folder to exist in the .azure-old location.

That triggers this condition as the feature expects to be able to create a symlink in $HOME/.azure to point cliextensions to the .azure-old folder.

[stuartleeks]

One thought was to allow installing az CLI extensions via the azure-cli-persistence feature so that they can be installed after the persistence has been set up.

However, this becomes something that you have to know to do.

It also doesn't handle the case where the azure-cli-persistence is configured as a default feature and the user opens a dev container that doesn't explicitly use the feature (i.e. a scenario I often encounter)

[stuartleeks]

An alternative would be to try to merge the cliextensions contents from the .azure-old folder (i.e. where the azure-cli feature installs to) into the persisted folder.

One downside of this is that if you trigger this behaviour then once an extension is installed by the azure-cli extension it will be copied into the persisted folder. Removing the extension from the devcontainer.json and rebuilding won't remove the extension as it will still reside in the persisted folder.

[stuartleeks]

On the merge idea, we could add a marker file in feature folders that we copy into the volume. Then if the corresponding extension folder doesn't exist in the original cliextensions folder and has the marker file we can remove it from the cliextensions folder in the volume?