`Multiple updates of variable` aren't that helpful

[shonfeder]

Given

module M {

   var v: int

   action duplicate_update = all {
     v' = 1,
     v' = 0,
   }

}

The effect checker correctly raises an error due to the duplicate updates of v:

$  quint typecheck f.qnt 
/quint/f.qnt:3:4 - error: [QNT202] Multiple updates of variable v
3:    var v: int
      ^^^^^^^^^^

error: typechecking failed

However this error only points the location where the variable is declared, which is not where the error is arising, and it doesn't help identifying where the duplicate updates arise. This can be very tricky in larger specs with layers of action abstractions.

Instead, the error should give a list of all conflicting update locations.

This issue is thanks to a report from @crodriguezvega. Thanks, Carlos!

[konnov]

I have changed the label to usability, since it is not actually a bug. Nothing is breaking.

[shonfeder]

I'm fine with that label change. To explain my labeling: imo this is pointing to the wrong location, which is why I viewed it as a bug.