You are getting this deprecation notice cause a library somewhere is requiring iconv.
iconv is a gem created by Matz that can be used to convert strings from one format to another.
For example this is often used:
Iconv.iconv('UTF-8//IGNORE', 'UTF-8', content) this little bit of magic takes a UTF-8 string that may have invalid chars and converts it to a proper UTF-8 string.
It has been decided that in Ruby 1.9.3 we should not be using iconv any more and instead use the built-in String#encode. encode is more powerful and allows you more flexibility.
The theory is that the above example could be replaced with:
string.encode("UTF-8", :invalid => :replace, :undef => :replace, :replace => "?")
In practice it seems this is imperfect.
This also leads to a less than easy story for gem creators who wish to support 1.8:
content = RUBY_VERSION.to_f < 1.9 ?
Iconv.iconv('UTF-8//IGNORE', 'UTF-8', "content") :
"#{content}".encode(Encoding::UTF_8, :invalid => :replace, :undef => :replace, :replace => '')
So, you have a gem somewhere that is requiring iconv, to find it:
Assuming your error message is: /gems/activesupport-3.1.0/lib/active_support/dependencies.rb:240
Open up /gems/activesupport-3.1.0/lib/active_support/dependencies.rb on line 240:
Add the line:
p caller if file =~ /iconv/
(just after: load_dependency(file) { result = super })
You will get a big fat stack trace:
rake --tasks /home/sam/.rvm/gems/ruby-1.9.3-p125/gems/activesupport-3.2.6/lib/active_support/dependencies.rb:251:in `block in require': iconv will be deprecated in the future, use String#encode instead. ["/home/sam/.rvm/gems/ruby-1.9.3-p125/gems/calais-0.0.13/lib/calais.rb:5:in `'", .. more omitted ..
This tells me it is the calais gem. Looking through pull requests, I am not the first. The pull has not been yanked in.
Depending on the gem, there may be an upgraded version that does not have this error, so I would recommend you upgrade your gems first. If you are unlucky you may be stuck with the unfortunate task of forking a gem to get rid of this (if for example your pull request to fix it languishes)