Don't type test against interfaces (#1873)

Author: alfonsogarciacaro

src/Components/Fsi.fs

@@ -420,8 +420,7 @@ module Fsi =
             let! profile =
                 match provider.provideTerminalProfile (ctok) with
                 | None -> promise.Return None
-                | Some(U2.Case1 options) -> promise.Return(Some options)
-                | Some(U2.Case2 work) -> Promise.ofThenable work
+                | Some work -> work |> Promise.ofMaybeThenable Some
 
             let profile =
                 match profile with
@@ -431,10 +430,7 @@ module Fsi =
 
                     failwith "unable to spawn FSI"
 
-            let terminal =
-                match profile.options with
-                | U2.Case1 opts -> window.createTerminal opts
-                | U2.Case2 opts -> window.createTerminal opts
+            let terminal = window.createTerminal !!profile.options
 
             // Wait for the new terminal to be ready
             let! newTerminal =

src/Components/SolutionExplorer.fs

@@ -442,8 +442,10 @@ module SolutionExplorer =
                 ti.id <-
                     let label (ti: TreeItem) =
                         match ti.label with
-                        | Some(U2.Case1 l) -> l
-                        | Some(U2.Case2 l) -> l.label
+                        | Some(l) ->
+                            match box l with
+                            | :? string as l -> l
+                            | l -> (l :?> TreeItemLabel).label
                         | None -> ""
 
                     match element with

src/Core/Utils.fs

@@ -284,6 +284,14 @@ module Promise =
     let ofThenable (t: Thenable<'t>) : JS.Promise<'t> = unbox (box t)
     let toThenable (p: JS.Promise<'t>) : Thenable<'t> = unbox (box p)
 
+    [<Emit("typeof ($0 || {}).then === 'function'")>]
+    let isThenable (x: obj) : bool = jsNative
+
+    let ofMaybeThenable (ifValue: 'T1 -> 'T2) (t: U2<'T1, Thenable<'T2>>) : JS.Promise<'T2> =
+        match box t with
+        | t when isThenable t -> unbox t |> ofThenable
+        | t -> unbox t |> ifValue |> Promise.lift
+
     let onSuccess = Promise.tap
 
     // source: https://github.com/ionide/ionide-vscode-helpers/blob/5e4c28c79ed565497cd481fac2f22ee2d8d28406/src/Helpers.fs#L92