Cleaned up alias permutations, fixed empty aliases

src/Discord.Net.Commands/Builders/CommandBuilder.cs

@@ -72,7 +72,11 @@ namespace Discord.Commands.Builders
 
         public CommandBuilder AddAliases(params string[] aliases)
         {
-            _aliases.AddRange(aliases);
+            for (int i = 0; i < aliases.Length; i++)
+            {
+                if (!_aliases.Contains(aliases[i]))
+                    _aliases.Add(aliases[i]);
+            }
             return this;
         }
         public CommandBuilder AddPrecondition(PreconditionAttribute precondition)

src/Discord.Net.Commands/Builders/ModuleBuilder.cs

@@ -58,9 +58,13 @@ namespace Discord.Commands.Builders
             return this;
         }
 
-        public ModuleBuilder AddAlias(params string[] newAliases)
+        public ModuleBuilder AddAlias(params string[] aliases)
         {
-            _aliases.AddRange(newAliases);
+            for (int i = 0; i < aliases.Length; i++)
+            {
+                if (!_aliases.Contains(aliases[i]))
+                    _aliases.Add(aliases[i]);
+            }
             return this;
         }
         public ModuleBuilder AddPrecondition(PreconditionAttribute precondition)

src/Discord.Net.Commands/Info/CommandInfo.cs

@@ -41,24 +41,19 @@ namespace Discord.Commands
 
             RunMode = (builder.RunMode == RunMode.Default ? service._defaultRunMode : builder.RunMode);
             Priority = builder.Priority;
-
-            // both command and module provide aliases
-            if (module.Aliases.Count > 0 && builder.Aliases.Count > 0)
-            {
-                Aliases = module.Aliases
-                    .Permutate(builder.Aliases, (first, second) => second != null ? first + service._separatorChar + second : first)
-                    .Select(x => service._caseSensitive ? x : x.ToLowerInvariant())
-                    .ToImmutableArray();
-            }
-            // only module provides aliases
-            else if (module.Aliases.Count > 0)
-                Aliases = module.Aliases.Select(x => service._caseSensitive ? x : x.ToLowerInvariant()).ToImmutableArray();
-            // only command provides aliases
-            else if (builder.Aliases.Count > 0)
-                Aliases = builder.Aliases.Select(x => service._caseSensitive ? x : x.ToLowerInvariant()).ToImmutableArray();
-            // neither provide aliases
-            else
-                throw new InvalidOperationException("Cannot build a command without any aliases");
+            
+            Aliases = module.Aliases
+                .Permutate(builder.Aliases, (first, second) =>
+                {
+                    if (first == "")
+                        return second;
+                    else if (second == "")
+                        return first;
+                    else
+                        return first + service._separatorChar + second;
+                })
+                .Select(x => service._caseSensitive ? x : x.ToLowerInvariant())
+                .ToImmutableArray();
 
             Preconditions = builder.Preconditions.ToImmutableArray();
 

src/Discord.Net.Commands/Info/ModuleInfo.cs

@@ -15,7 +15,7 @@ namespace Discord.Commands
         public string Remarks { get; }
 
         public IReadOnlyList<string> Aliases { get; }
-        public IEnumerable<CommandInfo> Commands { get; }
+        public IReadOnlyList<CommandInfo> Commands { get; }
         public IReadOnlyList<PreconditionAttribute> Preconditions { get; }
         public IReadOnlyList<ModuleInfo> Submodules { get; }
         public ModuleInfo Parent { get; }
@@ -31,7 +31,7 @@ namespace Discord.Commands
             Parent = parent;
 
             Aliases = BuildAliases(builder).ToImmutableArray();
-            Commands = builder.Commands.Select(x => x.Build(this, service));
+            Commands = builder.Commands.Select(x => x.Build(this, service)).ToImmutableArray();
             Preconditions = BuildPreconditions(builder).ToImmutableArray();
 
             Submodules = BuildSubmodules(builder, service).ToImmutableArray();