Workaround for emptying FSharp.Editor cache due to duplicate ProjectSystem events (#13313) (#13396)

Co-authored-by: Petr Semkin <psfinaki@users.noreply.github.com>

Co-authored-by: Vlad Zarytovskii <vzaritovsky@hotmail.com>
Co-authored-by: Petr Semkin <psfinaki@users.noreply.github.com>

Author: 3 people

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

@@ -346,7 +346,7 @@ type internal HackCpsCommandLineChanges
     /// This handles commandline change notifications from the Dotnet Project-system
     /// Prior to VS 15.7 path contained path to project file, post 15.7 contains target binpath
     /// binpath is more accurate because a project file can have multiple in memory projects based on configuration
-    member _.HandleCommandLineChanges(path:string, sources:ImmutableArray<CommandLineSourceFile>, _references:ImmutableArray<CommandLineReference>, options:ImmutableArray<string>) =
+    member _.HandleCommandLineChanges(path:string, sources:ImmutableArray<CommandLineSourceFile>, references:ImmutableArray<CommandLineReference>, options:ImmutableArray<string>) =
         use _logBlock = Logger.LogBlock(LogEditorFunctionId.LanguageService_HandleCommandLineArgs)
 
         let projectId =
@@ -363,5 +363,11 @@ type internal HackCpsCommandLineChanges
 
         let sourcePaths = sources |> Seq.map(fun s -> getFullPath s.Path) |> Seq.toArray
 
-        let workspaceService = workspace.Services.GetRequiredService<IFSharpWorkspaceService>()
-        workspaceService.FSharpProjectOptionsManager.SetCommandLineOptions(projectId, sourcePaths, options)
+        /// Due to an issue in project system, when we close and reopen solution, it sends the CommandLineChanges twice for every project.
+        /// First time it sends a correct path, sources, references and options.
+        /// Second time it sends a correct path, empty sources, empty references and empty options, and we rewrite our cache, and fail to colourize the document later.
+        /// As a workaround, until we have a fix from PS or will move to Roslyn as a source of truth, we will not overwrite the cache in case of empty lists.
+
+        if not (sources.IsEmpty && references.IsEmpty && options.IsEmpty) then
+            let workspaceService = workspace.Services.GetRequiredService<IFSharpWorkspaceService>()
+            workspaceService.FSharpProjectOptionsManager.SetCommandLineOptions(projectId, sourcePaths, options)