Run rules as tasks only if they are allowed

Rules are filtered prior to creating tasks (threads). This avoids
creating unnecessary tasks as opposed to the earlier approach where
rule invocation was decided within their corresponding tasks.

Author: Kapil Borle

Engine/ScriptAnalyzer.cs

@@ -1437,14 +1437,14 @@ public IEnumerable<DiagnosticRecord> AnalyzeSyntaxTree(
             string fileName = filePathIsNullOrWhiteSpace ? String.Empty : System.IO.Path.GetFileName(filePath);
             if (this.ScriptRules != null)
             {
-                var tasks = this.ScriptRules.Select(scriptRule => Task.Factory.StartNew(() =>
-                {
-                    bool helpRule = String.Equals(scriptRule.GetName(), "PSUseUTF8EncodingForHelpFile", StringComparison.OrdinalIgnoreCase);
+                var allowedRules = this.ScriptRules.Where(IsRuleAllowed);
 
-                    if (IsRuleAllowed(scriptRule))
+                if (allowedRules.Any())
+                {
+                    var tasks = allowedRules.Select(scriptRule => Task.Factory.StartNew(() =>
                     {
+                        bool helpRule = String.Equals(scriptRule.GetName(), "PSUseUTF8EncodingForHelpFile", StringComparison.OrdinalIgnoreCase);
                         List<object> result = new List<object>();
-
                         result.Add(string.Format(CultureInfo.CurrentCulture, Strings.VerboseRunningMessage, scriptRule.GetName()));
 
                         // Ensure that any unhandled errors from Rules are converted to non-terminating errors
@@ -1478,26 +1478,26 @@ public IEnumerable<DiagnosticRecord> AnalyzeSyntaxTree(
                         }
 
                         verboseOrErrors.Add(result);
-                    }
-                }));
+                    }));
 
-                Task.Factory.ContinueWhenAll(tasks.ToArray(), t => verboseOrErrors.CompleteAdding());
+                    Task.Factory.ContinueWhenAll(tasks.ToArray(), t => verboseOrErrors.CompleteAdding());
 
-                while (!verboseOrErrors.IsCompleted)
-                {
-                    List<object> data = null;
-                    try
+                    while (!verboseOrErrors.IsCompleted)
                     {
-                        data = verboseOrErrors.Take();
-                    }
-                    catch (InvalidOperationException) { }
+                        List<object> data = null;
+                        try
+                        {
+                            data = verboseOrErrors.Take();
+                        }
+                        catch (InvalidOperationException) { }
 
-                    if (data != null)
-                    {
-                        this.outputWriter.WriteVerbose(data[0] as string);
-                        if (data.Count == 2)
+                        if (data != null)
                         {
-                            this.outputWriter.WriteError(data[1] as ErrorRecord);
+                            this.outputWriter.WriteVerbose(data[0] as string);
+                            if (data.Count == 2)
+                            {
+                                this.outputWriter.WriteError(data[1] as ErrorRecord);
+                            }
                         }
                     }
                 }