Allow ViewEvent.Context.additionalProperties to be mutable

[lgvalle]

Is your feature request related to a problem? Please describe.
The problem we're facing is we'd like to enrich ViewEvents with custom attributes but additionalProperties can't be modified

The approach we're following is to set up EventMapper<ViewEvent> to get a callback when a ViewEvent is generated.
As it's known you can't clone the viewEvent or it will be discarded. So only a few var properties can be modified. The Context.additionalProperties is a map that looks like the right place to add extra properties but unfortunately is not mutable.

Describe the solution you'd like
Change

public val additionalProperties: Map<String, Any?> = emptyMap(),

to

public var additionalProperties: Map<String, Any?> = emptyMap()

or alternatively to

public val additionalProperties: MutableMap<String, Any?> = mutableMapOf()

so extra properties can be added to ViewEvents

Describe alternatives you've considered
The alternative we've considered was to write a custom ViewTrackingStrategy that will create its own set of attributes to track, but it seems overkill for this

Additional context
Alternatively consider allowing the injection of custom rules on RumEventMapper regarding which events are dropped to, for example, allow events that are not the same instance (aka, allow .copy())

[xgouchet]

Hi @lgvalle , thanks alot for this feature request. Indeed for now we don't allow modification of the additional properties, but we are considering adding some APIs to allow enriching the view.
You can also add custom attributes through the GlobalRum.addAttribute() (and similar methods).

[0xnm]

Hello @lgvalle! ViewEvent.Context.additionalProperties is now mutable (it has the type MutableMap<String, Any?>, this change was done in #1089) and was delivered in the release 1.15.0.

I'm closing this issue as your request was implemented, don't hesitate to re-open it if needed.