Variable substitution with environment - allow for fallback to default

When doing variable substitution with environment (at debugging launch, but could be useful for tasks too - ${env:Name}), I would like to provide a fallback (default) when the environment variable is not set.

As an example, see the variable substitution scheme for Docker Compose: https://docs.docker.com/compose/compose-file/#variable-substitution

• ${VARIABLE:-default} evaluates to default if VARIABLE is unset or empty in the environment.
• ${VARIABLE-default} evaluates to default only if VARIABLE is unset in the environment.

The syntax for VS Code could be ${env:Name:-default} and ${env:Name-default} with the same logic.

VS Code version 1.42.1

[alexr00]

Instead of using env you could write an extension that provides a command and use command input variables

[flying-sheep]

Any way to circumvent this for now? I want to do use XDG basedir spec and prepend something to XDG_DATA_DIRS.

To this end I need to retrieve the value of XDG_DATA_DIRS if it’s set and use a default when it isn’t set, which would look like this:

"env": {
    "XDG_DATA_DIRS": "${workspaceFolder}/something:${env:XDG_DATA_DIRS-/usr/local/share:/usr/share}"
}

There seems to be no way to currently do this in a launch configuration, and falling back to the empty string will break every GUI application launched with that env value set.