RunImmediate should use RunSynchronously if called on UI thread

tests/benchmarks/CompilerServiceBenchmarks/Program.fs

@@ -2,14 +2,10 @@
 open System.IO
 open System.Text
 open System.Threading.Tasks
-open FSharp.Compiler.ErrorLogger
 open FSharp.Compiler.CodeAnalysis
 open FSharp.Compiler.Diagnostics
-open FSharp.Compiler.Syntax
-open FSharp.Compiler.Symbols
 open FSharp.Compiler.EditorServices
 open FSharp.Compiler.Text
-open FSharp.Compiler.AbstractIL
 open FSharp.Compiler.AbstractIL.IL
 open FSharp.Compiler.AbstractIL.ILBinaryReader
 open Microsoft.CodeAnalysis.Text

tests/service/Common.fs

@@ -6,6 +6,7 @@ open System.Diagnostics
 open System.IO
 open System.Collections.Generic
 open System.Collections.Immutable
+open System.Threading
 open System.Threading.Tasks
 open FSharp.Compiler.CodeAnalysis
 open FSharp.Compiler.IO

vsintegration/src/FSharp.Editor/Common/Extensions.fs

@@ -6,6 +6,7 @@ module internal Microsoft.VisualStudio.FSharp.Editor.Extensions
 open System
 open System.IO
 open System.Collections.Immutable
+open System.Threading
 open System.Threading.Tasks
 
 open Microsoft.CodeAnalysis
@@ -293,14 +294,17 @@ module Exception =
         |> String.concat " ---> "
 
 type Async with
-    static member RunImmediate (computation: Async<'T>, ?cancellationToken ) =
-        let cancellationToken = defaultArg cancellationToken Async.DefaultCancellationToken
-        let ts = TaskCompletionSource<'T>()
-        let task = ts.Task
-        Async.StartWithContinuations(
-            computation,
-            (fun k -> ts.SetResult k),
-            (fun exn -> ts.SetException exn),
-            (fun _ -> ts.SetCanceled()),
-            cancellationToken)
-        task.Result
+    static member RunImmediateExceptOnUI (computation: Async<'T>, ?cancellationToken ) =
+        match SynchronizationContext.Current with 
+        | null ->
+            let cancellationToken = defaultArg cancellationToken Async.DefaultCancellationToken
+            let ts = TaskCompletionSource<'T>()
+            let task = ts.Task
+            Async.StartWithContinuations(
+                computation,
+                (fun k -> ts.SetResult k),
+                (fun exn -> ts.SetException exn),
+                (fun _ -> ts.SetCanceled()),
+                cancellationToken)
+            task.Result
+        | _ -> Async.RunSynchronously(computation, ?cancellationToken=cancellationToken)

vsintegration/src/FSharp.Editor/Formatting/IndentationService.fs

@@ -107,4 +107,4 @@ type internal FSharpIndentationService
                     match indent with
                     | None -> Nullable()
                     | Some(indentation) -> Nullable<FSharpIndentationResult>(FSharpIndentationResult(sourceText.Lines.[lineNumber].Start, indentation))
-            } |> (fun c -> Async.RunImmediate(c,cancellationToken=cancellationToken))
+            } |> (fun c -> Async.RunImmediateExceptOnUI(c,cancellationToken=cancellationToken))

vsintegration/src/FSharp.Editor/LanguageService/WorkspaceExtensions.fs

@@ -203,7 +203,7 @@ type Document with
         let workspaceService = this.Project.Solution.GetFSharpWorkspaceService()
         let parsingOptions, _, _ = 
             workspaceService.FSharpProjectOptionsManager.TryGetOptionsForDocumentOrProject(this, CancellationToken.None, nameof(this.SetFSharpProjectOptionsForTesting))
-            |> Async.RunImmediate
+            |> Async.RunImmediateExceptOnUI
             |> Option.get
         ProjectCache.Projects.Add(this.Project, (workspaceService.Checker, workspaceService.FSharpProjectOptionsManager, parsingOptions, projectOptions))
 

vsintegration/src/FSharp.Editor/Navigation/GoToDefinition.fs

@@ -473,7 +473,7 @@ type internal GoToDefinition(metadataAsSource: FSharpMetadataAsSourceService) =
                         }
 
                     let span =
-                        match Async.RunImmediate(goToAsync, cancellationToken = cancellationToken) with
+                        match Async.RunImmediateExceptOnUI(goToAsync, cancellationToken = cancellationToken) with
                         | Some span -> span
                         | _ -> TextSpan()