add unknown command resolution so use of _ is not necessary leafo/lapis-exceptions#3

Author: leafo

lapis/cmd/actions.lua

@@ -729,6 +729,26 @@ do
           self.default_action
         }
       end
+      local ok, result = parser:pparse(args)
+      if ok then
+        return result
+      end
+      local cmd_name = result:match("unknown command '(.-)'")
+      if cmd_name then
+        local mod_name = "lapis.cmd.actions." .. tostring(cmd_name)
+        if pcall(require, mod_name) then
+          local spec = custom_action({
+            name = cmd_name
+          })
+          table.insert(COMMANDS, spec)
+          local command = parser:command(cmd_name)
+          command:handle_options(false)
+          command:argument("sub_command_args", "Arguments to command"):argname("<args>"):args("*")
+          return parser:parse(args)
+        else
+          io.stderr:write("Note: tried to load command from module '" .. tostring(mod_name) .. "'\n")
+        end
+      end
       return parser:parse(args)
     end,
     execute = function(self, args)

lapis/cmd/actions.moon

@@ -615,6 +615,27 @@ class CommandRunner
     if next(args) == nil
       args = { @default_action }
 
+    ok, result = parser\pparse args
+
+    if ok
+      return result
+
+    -- try to load unknown command as a third-party action module
+    cmd_name = result\match "unknown command '(.-)'"
+    if cmd_name
+      mod_name = "lapis.cmd.actions.#{cmd_name}"
+      if pcall require, mod_name
+        spec = custom_action {name: cmd_name}
+        table.insert COMMANDS, spec
+
+        command = parser\command cmd_name
+        command\handle_options false
+        command\argument("sub_command_args", "Arguments to command")\argname("<args>")\args("*")
+        return parser\parse args
+      else
+        io.stderr\write "Note: tried to load command from module '#{mod_name}'\n"
+
+    -- re-run parse to trigger the original error message
     parser\parse args
 
   execute: (args) =>