Added a test plugin.

Volo.Abp.sln

@@ -88,6 +88,8 @@ Project("{8BB2217D-0F2D-49D1-97BC-3654ED321F3B}") = "Volo.Abp.MongoDB", "src\Vol
 EndProject
 Project("{8BB2217D-0F2D-49D1-97BC-3654ED321F3B}") = "AbpDesk.MongoBlog", "src\AbpDesk\AbpDesk.MongoBlog\AbpDesk.MongoBlog.xproj", "{63244DC7-34BE-44E1-BF6F-F2672E59AF36}"
 EndProject
+Project("{8BB2217D-0F2D-49D1-97BC-3654ED321F3B}") = "AbpDesk.SamplePlugInModule", "src\AbpDesk\AbpDesk.SamplePlugInModule\AbpDesk.SamplePlugInModule.xproj", "{ADFAF85B-B785-41EA-B57D-422775989FA6}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -214,6 +216,10 @@ Global
 		{63244DC7-34BE-44E1-BF6F-F2672E59AF36}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{63244DC7-34BE-44E1-BF6F-F2672E59AF36}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{63244DC7-34BE-44E1-BF6F-F2672E59AF36}.Release|Any CPU.Build.0 = Release|Any CPU
+		{ADFAF85B-B785-41EA-B57D-422775989FA6}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{ADFAF85B-B785-41EA-B57D-422775989FA6}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{ADFAF85B-B785-41EA-B57D-422775989FA6}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{ADFAF85B-B785-41EA-B57D-422775989FA6}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -257,5 +263,6 @@ Global
 		{4AB91077-82DC-4335-9274-BCE017BD9C8B} = {146F561E-C7B8-4166-9383-47E1BC1A2E62}
 		{B31FFAE3-5DAC-4E51-BD17-F7446B741A36} = {4C753F64-0C93-4D65-96C2-A40893AFC1E8}
 		{63244DC7-34BE-44E1-BF6F-F2672E59AF36} = {1187F469-0063-4065-9419-A1D956C80145}
+		{ADFAF85B-B785-41EA-B57D-422775989FA6} = {1187F469-0063-4065-9419-A1D956C80145}
 	EndGlobalSection
 EndGlobal

src/AbpDesk/AbpDesk.ConsoleDemo/AbpDesk/ConsoleDemo/Program.cs

@@ -1,6 +1,8 @@
 using System;
+using System.IO;
 using Microsoft.Extensions.DependencyInjection;
 using Volo.Abp;
+using Volo.Abp.Modularity.PlugIns;
 
 namespace AbpDesk.ConsoleDemo
 {
@@ -9,7 +11,12 @@ namespace AbpDesk.ConsoleDemo
         public static void Main(string[] args)
         {
             var services = new ServiceCollection();
-            var application = services.AddApplication<AbpDeskConsoleDemoModule>();
+
+            var application = services.AddApplication<AbpDeskConsoleDemoModule>(options =>
+            {
+                AddPlugIns(options);
+            });
+
             using (var scope = services.BuildServiceProvider().CreateScope())
             {
                 application.Initialize(scope.ServiceProvider);
@@ -46,5 +53,20 @@ namespace AbpDesk.ConsoleDemo
                 .GetRequiredService<BlogPostLister>()
                 .List();
         }
+
+        private static void AddPlugIns(AbpApplicationCreationOptions options)
+        {
+            options.PlugInSources.Add(
+                new FolderPlugInSource(
+                    Path.Combine(
+                        Directory.GetCurrentDirectory(),
+                        @"..\AbpDesk.SamplePlugInModule\bin\Debug\netstandard1.6\"
+                    )
+                )
+                {
+                    Filter = filePath => filePath.EndsWith("AbpDesk.SamplePlugInModule.dll")
+                }
+            );
+        }
     }
 }

src/AbpDesk/AbpDesk.SamplePlugInModule/AbpDesk.SamplePlugInModule.xproj

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <VisualStudioVersion Condition="'$(VisualStudioVersion)' == ''">14.0</VisualStudioVersion>
+    <VSToolsPath Condition="'$(VSToolsPath)' == ''">$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)</VSToolsPath>
+  </PropertyGroup>
+
+  <Import Project="$(VSToolsPath)\DotNet\Microsoft.DotNet.Props" Condition="'$(VSToolsPath)' != ''" />
+  <PropertyGroup Label="Globals">
+    <ProjectGuid>adfaf85b-b785-41ea-b57d-422775989fa6</ProjectGuid>
+    <RootNamespace>AbpDesk.SamplePlugInModule</RootNamespace>
+    <BaseIntermediateOutputPath Condition="'$(BaseIntermediateOutputPath)'=='' ">.\obj</BaseIntermediateOutputPath>
+    <OutputPath Condition="'$(OutputPath)'=='' ">.\bin\</OutputPath>
+    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <SchemaVersion>2.0</SchemaVersion>
+  </PropertyGroup>
+  <Import Project="$(VSToolsPath)\DotNet\Microsoft.DotNet.targets" Condition="'$(VSToolsPath)' != ''" />
+</Project>

src/AbpDesk/AbpDesk.SamplePlugInModule/AbpDeskSamplePlugInModule.cs

@@ -0,0 +1,17 @@
+using System;
+using Microsoft.Extensions.DependencyInjection;
+using Volo.Abp.Modularity;
+
+namespace AbpDesk.SamplePlugInModule
+{
+    /* This is just a sample plugin module to test loading plugin modules.
+     */
+
+    public class AbpDeskSamplePlugInModule : AbpModule
+    {
+        public override void ConfigureServices(IServiceCollection services)
+        {
+            
+        }
+    }
+}

src/AbpDesk/AbpDesk.SamplePlugInModule/Properties/AssemblyInfo.cs

@@ -0,0 +1,19 @@
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+// General Information about an assembly is controlled through the following
+// set of attributes. Change these attribute values to modify the information
+// associated with an assembly.
+[assembly: AssemblyConfiguration("")]
+[assembly: AssemblyCompany("")]
+[assembly: AssemblyProduct("AbpDesk.SamplePlugInModule")]
+[assembly: AssemblyTrademark("")]
+
+// Setting ComVisible to false makes the types in this assembly not visible
+// to COM components.  If you need to access a type in this assembly from
+// COM, set the ComVisible attribute to true on that type.
+[assembly: ComVisible(false)]
+
+// The following GUID is for the ID of the typelib if this project is exposed to COM
+[assembly: Guid("adfaf85b-b785-41ea-b57d-422775989fa6")]

src/AbpDesk/AbpDesk.SamplePlugInModule/project.json

@@ -0,0 +1,14 @@
+{
+  "version": "1.0.0-*",
+
+  "dependencies": {
+    "NETStandard.Library": "1.6.1",
+    "Volo.Abp": "1.0.0-*"
+  },
+
+  "frameworks": {
+    "netstandard1.6": {
+      "imports": "dnxcore50"
+    }
+  }
+}

src/Volo.Abp/Volo/Abp/Modularity/PlugIns/FolderPlugInSource.cs

@@ -1,6 +1,9 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.Loader;
 using JetBrains.Annotations;
 using Volo.Abp.Reflection;
 using Volo.ExtensionMethods.Collections.Generic;
@@ -13,7 +16,11 @@ namespace Volo.Abp.Modularity.PlugIns
 
         public SearchOption SearchOption { get; set; }
 
-        public FolderPlugInSource([NotNull] string folder, SearchOption searchOption = SearchOption.TopDirectoryOnly)
+        public Func<string, bool> Filter { get; set; }
+
+        public FolderPlugInSource(
+            [NotNull] string folder, 
+            SearchOption searchOption = SearchOption.TopDirectoryOnly)
         {
             Check.NotNull(folder, nameof(folder));
 
@@ -21,13 +28,11 @@ namespace Volo.Abp.Modularity.PlugIns
             SearchOption = searchOption;
         }
 
-        [NotNull]
         public Type[] GetModules()
         {
             var modules = new List<Type>();
 
-            var assemblies = AssemblyHelper.GetAllAssembliesInFolder(Folder, SearchOption);
-            foreach (var assembly in assemblies)
+            foreach (var assembly in GetAssemblies())
             {
                 try
                 {
@@ -47,5 +52,17 @@ namespace Volo.Abp.Modularity.PlugIns
 
             return modules.ToArray();
         }
+
+        private IEnumerable<Assembly> GetAssemblies()
+        {
+            var assemblyFiles = AssemblyHelper.GetAssemblyFiles(Folder, SearchOption);
+
+            if (Filter != null)
+            {
+                assemblyFiles = assemblyFiles.Where(Filter);
+            }
+
+            return assemblyFiles.Select(AssemblyLoadContext.Default.LoadFromAssemblyPath);
+        }
     }
 }

src/Volo.Abp/Volo/Abp/Modularity/PlugIns/PlugInSourceListExtensions.cs

@@ -6,14 +6,19 @@ namespace Volo.Abp.Modularity.PlugIns
 {
     public static class PlugInSourceListExtensions
     {
-        public static void AddFolder([NotNull] this PlugInSourceList list, [NotNull] string folder, SearchOption searchOption = SearchOption.TopDirectoryOnly)
+        public static void AddFolder(
+            [NotNull] this PlugInSourceList list, 
+            [NotNull] string folder, 
+            SearchOption searchOption = SearchOption.TopDirectoryOnly)
         {
             Check.NotNull(list, nameof(list));
 
             list.Add(new FolderPlugInSource(folder, searchOption));
         }
 
-        public static void AddTypes([NotNull] this PlugInSourceList list, params Type[] moduleTypes)
+        public static void AddTypes(
+            [NotNull] this PlugInSourceList list, 
+            params Type[] moduleTypes)
         {
             Check.NotNull(list, nameof(list));
 

src/Volo.Abp/Volo/Abp/Reflection/AssemblyHelper.cs

@@ -8,15 +8,18 @@ namespace Volo.Abp.Reflection
 {
     internal static class AssemblyHelper
     {
-        public static List<Assembly> GetAllAssembliesInFolder(string folderPath, SearchOption searchOption)
+        public static List<Assembly> LoadAssemblies(string folderPath, SearchOption searchOption)
         {
-            var assemblyFiles = Directory
+            return GetAssemblyFiles(folderPath, searchOption)
+                .Select(AssemblyLoadContext.Default.LoadFromAssemblyPath)
+                .ToList();
+        }
+
+        public static IEnumerable<string> GetAssemblyFiles(string folderPath, SearchOption searchOption)
+        {
+            return Directory
                 .EnumerateFiles(folderPath, "*.*", searchOption)
                 .Where(s => s.EndsWith(".dll") || s.EndsWith(".exe"));
-
-            //TODO: AssemblyLoadContext not tested
-
-            return assemblyFiles.Select(AssemblyLoadContext.Default.LoadFromAssemblyPath).ToList();
         }
     }
 }