Add support to load dlls in "_plugins" path

src/Pretzel.Logic/Templating/Jekyll/LiquidEngine.cs

@@ -4,6 +4,7 @@
 using Pretzel.Logic.Liquid;
 using Pretzel.Logic.Templating.Context;
 using Pretzel.Logic.Templating.Jekyll.Liquid;
+using System.Collections.Generic;
 
 namespace Pretzel.Logic.Templating.Jekyll
 {
@@ -13,6 +14,9 @@ public class LiquidEngine : JekyllEngineBase
     {
         SiteContextDrop contextDrop;
 
+        [ImportMany(AllowRecomposition = true)]
+        public IEnumerable<DotLiquid.Tag> Tags { get; set; }
+
         public LiquidEngine()
         {
             DotLiquid.Liquid.UseRubyDateFormat = true;
@@ -28,6 +32,16 @@ protected override void PreProcess()
                   Template.RegisterFilter(filter.GetType());
                }
             }
+            if (Tags != null)
+            {
+                var registerTagMethod = typeof(Template).GetMethod("RegisterTag", System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Static);
+
+                foreach (var tag in Tags)
+                {
+                    var registerTagGenericMethod = registerTagMethod.MakeGenericMethod(new[] { tag.GetType() });
+                    registerTagGenericMethod.Invoke(null, new[] { tag.Name });
+                }
+            }
         }
 
         Hash CreatePageData(PageContext pageContext)

src/Pretzel.Logic/Templating/JekyllEngineBase.cs

@@ -18,8 +18,8 @@ public abstract class JekyllEngineBase : ISiteEngine
 #pragma warning disable 0649
         [Import] public IFileSystem FileSystem { get; set; }
 #pragma warning restore 0649
-        
-        [ImportMany]
+
+        [ImportMany(AllowRecomposition = true)]
         public IEnumerable<IFilter> Filters { get; set; }
 
         public abstract void Initialize();

src/Pretzel/Program.cs

@@ -8,6 +8,7 @@
 using NDesk.Options;
 using Pretzel.Commands;
 using Pretzel.Logic.Extensions;
+using Pretzel.Logic.Commands;
 
 namespace Pretzel
 {
@@ -16,6 +17,10 @@ class Program
         [Import]
         private CommandCollection Commands { get; set; }
 
+        AggregateCatalog catalog;
+
+        CompositionContainer container;
+
         static void Main(string[] args)
         {
             Tracing.Logger.SetWriter(Console.Out);
@@ -64,6 +69,7 @@ private void Run(string[] args, OptionSet defaultSet)
                 return;
             }
 
+            LoadPlugins(commandArgs);
             Commands[commandName].Execute(commandArgs);
             WaitForClose();
         }
@@ -82,12 +88,26 @@ public void WaitForClose()
             }
         }
 
+        private void LoadPlugins(string[] commandArgs)
+        {
+            var parameters = container.GetExport<CommandParameters>().Value;
+            parameters.Parse(commandArgs);
+
+            var pluginsPath = System.IO.Path.Combine(parameters.Path, "_plugins");
+
+            if (System.IO.Directory.Exists(pluginsPath))
+            {
+                catalog.Catalogs.Add(new DirectoryCatalog(pluginsPath));
+            }
+        }
+
         public void Compose()
         {
             try
             {
                 var first = new AssemblyCatalog(Assembly.GetExecutingAssembly());
-                var container = new CompositionContainer(first);
+                catalog = new AggregateCatalog(first);
+                container = new CompositionContainer(catalog);
 
                 var batch = new CompositionBatch();
                 batch.AddExportedValue<IFileSystem>(new FileSystem());