Allow GetExecutableCommandsAsync(ModuleInfo) to recurse properly to all submodules.

src/Discord.Net.Commands/Discord.Net.Commands.csproj

@@ -6,6 +6,9 @@
     <Description>A Discord.Net extension adding support for bot commands.</Description>
     <TargetFrameworks>netstandard1.1</TargetFrameworks>
   </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Debug|netstandard1.1|AnyCPU'">
+    <LangVersion>7.3</LangVersion>
+  </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\Discord.Net.Core\Discord.Net.Core.csproj" />
   </ItemGroup>

src/Discord.Net.Commands/Extensions/CommandServiceExtensions.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using System.Threading.Tasks;
 
 namespace Discord.Commands
@@ -10,7 +9,7 @@ namespace Discord.Commands
         public static async Task<IReadOnlyCollection<CommandInfo>> GetExecutableCommandsAsync(this IEnumerable<CommandInfo> commands, ICommandContext context, IServiceProvider provider)
         {
             var executableCommands = new List<CommandInfo>();
-
+            
             foreach (var command in commands)
             {
                 var result = await command.CheckPreconditionsAsync(context, provider).ConfigureAwait(false);
@@ -22,7 +21,16 @@ namespace Discord.Commands
         }
         public static Task<IReadOnlyCollection<CommandInfo>> GetExecutableCommandsAsync(this CommandService commandService, ICommandContext context, IServiceProvider provider)
             => GetExecutableCommandsAsync(commandService.Commands, context, provider);
-        public static Task<IReadOnlyCollection<CommandInfo>> GetExecutableCommandAsync(this ModuleInfo module, ICommandContext context, IServiceProvider provider)
-            => GetExecutableCommandsAsync(module.Commands.Concat(module.Submodules.SelectMany(sm => sm.Commands)), context, provider);
+        public static async Task<IReadOnlyCollection<CommandInfo>> GetExecutableCommandsAsync(this ModuleInfo module, ICommandContext context, IServiceProvider provider)
+        {
+            var executableCommands = new List<CommandInfo>();
+
+            executableCommands.AddRange(await module.Commands.GetExecutableCommandsAsync(context, provider).ConfigureAwait(false));
+
+            foreach (var subModule in module.Submodules)
+                executableCommands.AddRange(await subModule.GetExecutableCommandsAsync(context, provider).ConfigureAwait(false));
+            
+            return executableCommands;
+        }
     }
 }