Add argument expansion support

README.asciidoc

@@ -629,6 +629,9 @@ Supported types are:
      option
  * `val`: value expansion, gives access to the environment variable available
      to the Shell expansion. The `kak_` prefix is not used there.
+ * `arg`: argument expansion, gives access to the arguments of the current
+     command, the content can be a number, or `#` for the argument count,
+     or `@` for all arguments concatenated.
 
 for example you can display last search pattern with
 

src/command_manager.cc

@@ -54,6 +54,7 @@ struct Token
         RegisterExpand,
         OptionExpand,
         ValExpand,
+        ArgExpand,
         CommandSeparator
     };
     Token() : m_type(Type::Raw) {}
@@ -198,6 +199,8 @@ Token::Type token_type(StringView type_name)
         return Token::Type::OptionExpand;
     else if (type_name == "val")
         return Token::Type::ValExpand;
+    else if (type_name == "arg")
+        return Token::Type::ArgExpand;
     else if (throw_on_invalid)
         throw unknown_expand{type_name};
     else
@@ -343,6 +346,20 @@ String expand_token(const Token& token, const Context& context,
             return it->value;
         return ShellManager::instance().get_val(content, context);
     }
+    case Token::Type::ArgExpand:
+    {
+        if (content == "#")
+            return to_string(shell_context.params.size());
+        else if (content == "@")
+            return join(shell_context.params, ' ');
+
+        const int arg = str_to_int(content)-1;
+        if (arg < 0)
+            throw runtime_error("invalid argument index");
+        if (arg < shell_context.params.size())
+            return shell_context.params[arg];
+        return {};
+    }
     case Token::Type::RawEval:
         return expand(content, context, shell_context);
     case Token::Type::Raw: