Provide a method to request a parser cancellation

Author: MDoerner

Rubberduck.Parsing/VBA/IParseManager.cs

@@ -9,7 +9,28 @@ public interface IParseManager
         event EventHandler<ParserStateEventArgs> StateChanged;
         event EventHandler<ParseProgressEventArgs> ModuleStateChanged;
 
+        /// <summary>
+        /// Requests reparse.
+        /// </summary>
+        /// <param name="requestor">The object requesting a reparse.</param>
         void OnParseRequested(object requestor);
+
+        /// <summary>
+        /// Requests cancellation of the current parse.
+        /// Always request a parse after requesting a cancellation.
+        /// Failing to do so leaves RD in an undefined state.
+        /// </summary>
+        /// <param name="requestor">The object requesting a reparse.</param>
+        void OnParseCancellationRequested(object requestor);
+
+        /// <summary>
+        /// Suspends the parser for the action provided after the current parse has finished.
+        /// Any incoming parse requests will be executed afterwards.
+        /// </summary>
+        /// <param name="requestor">The object requesting a reparse.</param>
+        /// <param name="allowedRunStates">The states in which the action may be performed.</param>
+        /// <param name="busyAction">The action to perform.</param> 
+        /// <param name="millisecondsTimeout">The timeout for waiting on the current parse to finish.</param> 
         SuspensionResult OnSuspendParser(object requestor, IEnumerable<ParserState> allowedRunStates, Action busyAction, int millisecondsTimeout = -1);
         void MarkAsModified(QualifiedModuleName module);
     }

Rubberduck.Parsing/VBA/ParseCoordinator.cs

@@ -69,6 +69,7 @@ public ParseCoordinator(
             _rewritingManager = rewritingManager;
 
             state.ParseRequest += ReparseRequested;
+            state.ParseCancellationRequested += ParseCancellationRequested;
             state.SuspendRequest += SuspendRequested;
 
             _requestorStack = new ConcurrentStack<object>();
@@ -99,6 +100,14 @@ private void ReparseRequested(object sender, EventArgs e)
             BeginParse(sender);
         }
 
+        private void ParseCancellationRequested(object requestor, EventArgs e)
+        {
+            lock (CancellationSyncObject)
+            {
+                Cancel();
+            }
+        }
+
         public void SuspendRequested(object sender, RubberduckStatusSuspendParserEventArgs e)
         {
             if (ParsingSuspendLock.IsReadLockHeld)

Rubberduck.Parsing/VBA/RubberduckParserState.cs

@@ -127,6 +127,7 @@ public sealed class RubberduckParserState : IDisposable, IDeclarationFinderProvi
             new ConcurrentDictionary<QualifiedModuleName, ModuleState>();
 
         public event EventHandler<EventArgs> ParseRequest;
+        public event EventHandler<EventArgs> ParseCancellationRequested;
         public event EventHandler<RubberduckStatusSuspendParserEventArgs> SuspendRequest;
         public event EventHandler<RubberduckStatusMessageEventArgs> StatusMessageUpdate;
 
@@ -963,14 +964,7 @@ public bool RemoveDeclaration(Declaration declaration)
             return _moduleStates[key].Declarations.TryRemove(declaration, out _);
         }
 
-        /// <summary>
-        /// Ensures parser state accounts for built-in declarations.
-        /// </summary>
-        /// <summary>
-        /// Requests reparse for specified component.
-        /// Omit parameter to request a full reparse.
-        /// </summary>
-        /// <param name="requestor">The object requesting a reparse.</param>
+        /// <inheritdoc />
         public void OnParseRequested(object requestor)
         {
             var handler = ParseRequest;
@@ -981,6 +975,18 @@ public void OnParseRequested(object requestor)
             }
         }
 
+        /// <inheritdoc />
+        public void OnParseCancellationRequested(object requestor)
+        {
+            var handler = ParseCancellationRequested;
+            if (handler != null && IsEnabled)
+            {
+                var args = EventArgs.Empty;
+                handler.Invoke(requestor, args);
+            }
+        }
+
+        /// <inheritdoc />
         public SuspensionResult OnSuspendParser(object requestor, IEnumerable<ParserState> allowedRunStates, Action busyAction, int millisecondsTimeout = NoTimeout)
         {
             if (millisecondsTimeout < NoTimeout)