$__contains requires hardcoded "all" value

[taleena]

Discussed in #1023

^{Originally posted by nadav-dav September 17, 2024}
When using the $__contains macro with a variable, you require to use the value "all" to indicates to the macro not to apply a filter there.

// if $env == "foo"
| where $__contains(env, $env)
this will become
| where env == "foo"


// if $env == "all"
| where $__contains(env, $env)
this will become
| where 1 == 1

But if you are using Prometheus in the same dashboard, the "all" value must be equal to .*.
That means that you have to either have 2 different variables for the same meaning, just with different "all" value, or to write something like:

| where "$env" == ".*" or $__contains(env, $env)

My suggestion is to have the ability to customize the "all" value in the datasource level so it could be multiple options like ("all", ".", "", etc...)