Enable command lookup caching by name and filter

Add a struct to use as a private struct to use as a key for the command
lookup cache.  Also re-enable caching in Helper.GetCommandInfo.

Author: SeeminglyScience

Engine/Helper.cs

@@ -28,7 +28,7 @@ public class Helper
         private readonly static Version minSupportedPSVersion = new Version(3, 0);
         private Dictionary<string, Dictionary<string, object>> ruleArguments;
         private PSVersionTable psVersionTable;
-        private Dictionary<string, CommandInfo> commandInfoCache;
+        private Dictionary<CommandLookupKey, CommandInfo> commandInfoCache;
 
         #endregion
 
@@ -142,7 +142,7 @@ public void Initialize()
             ruleArguments = new Dictionary<string, Dictionary<string, object>>(StringComparer.OrdinalIgnoreCase);
             if (commandInfoCache == null)
             {
-                commandInfoCache = new Dictionary<string, CommandInfo>(StringComparer.OrdinalIgnoreCase);
+                commandInfoCache = new Dictionary<CommandLookupKey, CommandInfo>();
             }
 
             IEnumerable<CommandInfo> aliases = this.invokeCommand.GetCommands("*", CommandTypes.Alias, true);
@@ -700,15 +700,16 @@ public CommandInfo GetCommandInfoLegacy(string name, CommandTypes? commandType =
                 cmdletName = name;
             }
 
+            var key = new CommandLookupKey(name, commandType);
             lock (getCommandLock)
             {
-                if (commandInfoCache.ContainsKey(cmdletName))
+                if (commandInfoCache.ContainsKey(key))
                 {
-                    return commandInfoCache[cmdletName];
+                    return commandInfoCache[key];
                 }
 
                 var commandInfo = GetCommandInfoInternal(cmdletName, commandType);
-                commandInfoCache.Add(cmdletName, commandInfo);
+                commandInfoCache.Add(key, commandInfo);
                 return commandInfo;
             }
         }
@@ -726,15 +727,16 @@ public CommandInfo GetCommandInfo(string name, CommandTypes? commandType = null)
                 return null;
             }
 
+            var key = new CommandLookupKey(name, commandType);
             lock (getCommandLock)
             {
-                if (commandInfoCache.ContainsKey(name))
+                if (commandInfoCache.ContainsKey(key))
                 {
-                    return commandInfoCache[name];
+                    return commandInfoCache[key];
                 }
 
                 var commandInfo = GetCommandInfoInternal(name, commandType);
-
+                commandInfoCache.Add(key, commandInfo);
                 return commandInfo;
             }
         }
@@ -1910,6 +1912,37 @@ public Version GetPSVersion()
         }
 
 #endregion Methods
+
+        private struct CommandLookupKey : IEquatable<CommandLookupKey>
+        {
+            private readonly string Name;
+
+            private readonly CommandTypes CommandTypes;
+
+            internal CommandLookupKey(string name, CommandTypes? commandTypes)
+            {
+                Name = name;
+                CommandTypes = commandTypes ?? CommandTypes.All;
+            }
+
+            public bool Equals(CommandLookupKey other)
+            {
+                return CommandTypes == other.CommandTypes
+                    && Name.Equals(other.Name, StringComparison.OrdinalIgnoreCase);
+            }
+
+            public override int GetHashCode()
+            {
+                // Algorithm from https://stackoverflow.com/questions/1646807/quick-and-simple-hash-code-combinations
+                unchecked
+                {
+                    int hash = 17;
+                    hash = hash * 31 + Name.ToUpperInvariant().GetHashCode();
+                    hash = hash * 31 + CommandTypes.GetHashCode();
+                    return hash;
+                }
+            }
+        }
     }