mystery: chef-client/knife: they are ignoring any error in knife.rb and client.rb

Question

I happened find that in ~/.chef/knife.rb or /etc/chef/client.rb, any error will be ignored by knife or chef-client.

...
a_non_exist_method a_non_exist_var
...
puts "==== #{a_non_exist_method}"

it is totally fine, even if the a_non_exist_method a_non_exist_var is absolutely wrong. The result will be of course

==== 

How does chef-client/knife execute client.rb/knife.rb?

PS: I know knife.rb and client.rb is a config file, not supposed to add user program logic there, just curious that why it put anything in it without error?

Answer 1

It is evaluated as a Chef::Config class instance, which inherit from mixlib-config, which depending on how you tested that may not be in strict mode (relevant code)

So you may end up with a property ignored without warning nor error when not setting strict mode.

Your puts just get evaluated as standard ruby, string interpolation search for a variable even if you called it a_non_exist_method and from ruby duck typing, it's a nil value, wich interpolated as string is an empty string.