Introduce high priority state changed event

The order in which event handlers are executed is not guaranteed. Because of this we had the problem that the status message change for the state change to Ready happened after the status message change in the inspections, which are executed async. As the result, the message 'Inspection' was immediately overwritten and did not last until the inspections had  finished.

Author: MDoerner

Rubberduck.Core/UI/Command/MenuItems/CommandBars/RubberduckCommandBar.cs

@@ -4,7 +4,6 @@
 using System.Linq;
 using System.Runtime.InteropServices;
 using Rubberduck.Resources;
-using Rubberduck.Parsing;
 using Rubberduck.Parsing.Symbols;
 using Rubberduck.Parsing.UIContext;
 using Rubberduck.Parsing.VBA;
@@ -15,18 +14,18 @@ namespace Rubberduck.UI.Command.MenuItems.CommandBars
     public class RubberduckCommandBar : AppCommandBarBase, IDisposable
     {
         private readonly IContextFormatter _formatter;
-        private readonly IParseCoordinator _parser;
+        private readonly RubberduckParserState _state;
         private readonly ISelectionChangeService _selectionService;
 
-        public RubberduckCommandBar(IParseCoordinator parser, IEnumerable<ICommandMenuItem> items, IContextFormatter formatter, ISelectionChangeService selectionService, IUiDispatcher uiDispatcher) 
+        public RubberduckCommandBar(RubberduckParserState state, IEnumerable<ICommandMenuItem> items, IContextFormatter formatter, ISelectionChangeService selectionService, IUiDispatcher uiDispatcher) 
             : base("Rubberduck", CommandBarPosition.Top, items, uiDispatcher)
         {
-            _parser = parser;
+            _state = state;
             _formatter = formatter;
             _selectionService = selectionService;
 
-            _parser.State.StateChanged += OnParserStateChanged;
-            _parser.State.StatusMessageUpdate += OnParserStatusMessageUpdate;
+            _state.StateChangedHighPriority += OnParserStateChanged;
+            _state.StatusMessageUpdate += OnParserStatusMessageUpdate;
             _selectionService.SelectionChanged += OnSelectionChange;
         }
 
@@ -36,14 +35,14 @@ public override void Initialize()
         {
             base.Initialize();
             SetStatusLabelCaption(ParserState.Pending);
-            EvaluateCanExecute(_parser.State);
+            EvaluateCanExecute(_state);
         }
 
         private Declaration _lastDeclaration;
         private ParserState _lastStatus = ParserState.None;
         private void EvaluateCanExecute(RubberduckParserState state, Declaration selected)
         {
-            var currentStatus = _parser.State.Status;
+            var currentStatus = _state.Status;
             if (_lastStatus == currentStatus && 
                 (selected == null || selected.Equals(_lastDeclaration)) &&
                 (selected != null || _lastDeclaration == null))
@@ -69,7 +68,7 @@ private void OnSelectionChange(object sender, DeclarationChangedEventArgs e)
             var description = e.Declaration?.DescriptionString ?? string.Empty;
             //& renders the next character as if it was an accelerator.
             SetContextSelectionCaption(caption?.Replace("&", "&&"), refCount, description);
-            EvaluateCanExecute(_parser.State, e.Declaration);
+            EvaluateCanExecute(_state, e.Declaration);
         }
 
 
@@ -82,14 +81,14 @@ private void OnParserStatusMessageUpdate(object sender, RubberduckStatusMessageE
                 message = RubberduckUI.ParserState_LoadingReference;
             }
 
-            SetStatusLabelCaption(message, _parser.State.ModuleExceptions.Count);            
+            SetStatusLabelCaption(message, _state.ModuleExceptions.Count);            
         }
 
         private void OnParserStateChanged(object sender, EventArgs e)
         {
-            _lastStatus = _parser.State.Status;
-            EvaluateCanExecute(_parser.State);    
-            SetStatusLabelCaption(_parser.State.Status, _parser.State.ModuleExceptions.Count);                 
+            _lastStatus = _state.Status;
+            EvaluateCanExecute(_state);    
+            SetStatusLabelCaption(_state.Status, _state.ModuleExceptions.Count);                 
         }
 
         public void SetStatusLabelCaption(ParserState state, int? errorCount = null)
@@ -182,8 +181,8 @@ protected virtual void Dispose(bool disposing)
             }
 
             _selectionService.SelectionChanged -= OnSelectionChange;
-            _parser.State.StateChanged -= OnParserStateChanged;
-            _parser.State.StatusMessageUpdate -= OnParserStatusMessageUpdate;
+            _state.StateChanged -= OnParserStateChanged;
+            _state.StatusMessageUpdate -= OnParserStatusMessageUpdate;
 
             RemoveCommandBar();
 

Rubberduck.Parsing/VBA/RubberduckParserState.cs

@@ -359,6 +359,7 @@ public IReadOnlyList<Tuple<QualifiedModuleName, SyntaxErrorException>> ModuleExc
             }
         }
 
+        public event EventHandler<ParserStateEventArgs> StateChangedHighPriority;
         public event EventHandler<ParserStateEventArgs> StateChanged;
 
         private int _stateChangedInvocations;
@@ -367,6 +368,27 @@ private void OnStateChanged(object requestor, CancellationToken token, ParserSta
             Interlocked.Increment(ref _stateChangedInvocations);
 
             Logger.Info($"{nameof(RubberduckParserState)} ({_stateChangedInvocations}) is invoking {nameof(StateChanged)} ({Status})");
+
+            var highPriorityHandler = StateChangedHighPriority;
+            if (highPriorityHandler != null && !token.IsCancellationRequested)
+            {
+                try
+                {
+                    var args = new ParserStateEventArgs(state, oldStatus, token);
+                    highPriorityHandler.Invoke(requestor, args);
+                }
+                catch (OperationCanceledException cancellation)
+                {
+                    throw;
+                }
+                catch (Exception e)
+                {
+                    // Error state, because this implies consumers are not exception-safe!
+                    // this behaviour could leave us in a state where some consumers have correctly updated and some have not
+                    Logger.Error(e, "An exception occurred when notifying consumers of updated parser state.");
+                }
+            }
+
             var handler = StateChanged;
             if (handler != null && !token.IsCancellationRequested)
             {