Duplicate Find All References results after a closed and re-opened .NET Core 2.0 project

[vasily-kirichenko]

1. Clone and build this project: https://github.com/fable-compiler/fable-suave-scaffold
2. Open ClientServer.sln.
3. Observe that things work.
4. Add a new file that defines the following:

    type private MaybeBuilder() = 
        member x.Bind(v, f) = Option.bind f v
        member x.Return(v) = Some v
        member x.Zero() = Some ()
        member x.Combine(v, f:unit -> _) = Option.bind f v
        member x.Delay(f : unit -> 'T) = f
        member x.Run(f) = f()
        member x.While(cond, f) =
            if cond() then x.Bind(f(), fun _ -> x.While(cond, f)) 
            else x.Zero()

    let private maybe = MaybeBuilder()

    let testFxn =
        let ret = 
            maybe {
                let! x = Some 1
                let! y = Some 2
                return x + y
            }
        ret

4. Close ClientServer.sln.
5. Re-open it.
6. Find All References on a maybe.

You will see duplicate results in the Find All References window.

Old issue:

[cartermp]

I cannot repro this on a .NET Core 2.0 project after #3564 in the 15.5 build.

[cartermp]

Interestingly enough, this does repro after I close and reopen the solution.

[cartermp]

This no longer reproduces. I believe all issues with duplicates have long been resolved.