zombie_scout

Find dead methods in your Ruby app

zom·bie code noun Undead code that shambles around your repository, and eats your brains.

You don't want zombie code around. But you can't spend all your time looking for it. So get yourself a Zombie Scout.

Zombie Scout is light & quick. Its only tools are parser and grep. It parses your code to find method declarations, and then greps through your project's source, looking for each method. If Zombie Scout can't find any calls to a method, it presumes the method is dead, and reports back to you.

How Does It Work?

Phase 1: Parse

Zombie Scout parses your ruby files, and remembers all the methods it sees defined.

Phase 2: Grep

Then it greps your whole project - currently *.rb, *.erb, and *.haml files - for whole-word occurrances of any of the methods it found. The whole-word grep (grep -w) means that searching for dead_method won't count dead_methods as a match, and accidentally think it's live.

So, if you have 1,000 methods, you have to run 1,000 greps? That's slow, right? Good news: back in Phase 1, when Zombie Scout parsed your code, it also remembered all the method CALLS it saw, and it automatically counts those methods as not-zombies, so it saves a bunch of time by not grepping for them.

Fair Warning

Zombie Scout isn't exhaustive or thorough - it's a scout, not a spy. (That could be another project, though - a Zombie Spy.)

If you generate methods in a way that's hard to grep for...

method_name = ['s', 'e', 'c', 'r', 'e', 't']
object.send(method_name.join(''))

...then Zombie Scout won't find it. Remember: light & quick.

That said, it will find methods defined with attr_reader & friends, or Forwardable delegates, or Rails scopes. Rails delegators are on the To-Do list.

If you have methods that are used by another library - say, callbacks - Zombie Scout will probably think they're dead, because it's not looking at the source for that other library.

Finally, if you have a method named after a common human-language word, and that word appears in (say) hard-coded strings or comments, Zombie Scout will think it's calling the method, and assume that the method is used.

# this is an awesome method!   <-- false positive right there
def awesome
  'AWESOME!'
end

Be wise.

Installation

The basics:

gem install 'zombie_scout'

Or, add this to your Gemfile:

gem 'zombie_scout'

Usage

From the Command Line

You can run it on a whole folder:

dan@aleph:~/projects/zombie_scout$ zombie_scout scout
Scouted 48 methods in 10 files, in 1.470468836 seconds.
Found 13 potential zombies, with a combined flog score of 66.9.

lib/zombie_scout/parser.rb:45   ZombieScout::Parser#on_send     8.3
lib/zombie_scout/parser.rb:17   ZombieScout::Parser#on_class    7.9
lib/zombie_scout/parser.rb:25   ZombieScout::Parser#on_module   7.2
lib/zombie_scout/parser.rb:39   ZombieScout::Parser#on_defs     5.9
lib/zombie_scout/parser.rb:81   ZombieScout::Parser#handle_def_delegators       5.8
lib/zombie_scout/parser.rb:72   ZombieScout::Parser#handle_attr_accessor        5.6
lib/zombie_scout/parser.rb:33   ZombieScout::Parser#on_def      4.9
lib/zombie_scout/parser.rb:56   ZombieScout::Parser#handle_attr_reader  4.3
lib/zombie_scout/parser.rb:64   ZombieScout::Parser#handle_attr_writer  4.3
lib/zombie_scout/parser.rb:89   ZombieScout::Parser#handle_def_delegator        3.8
lib/zombie_scout/parser.rb:95   ZombieScout::Parser#handle_scope        3.8
lib/zombie_scout/parser.rb:122  ZombieScout::ConstExtracter#on_const    2.7
lib/zombie_scout/parser.rb:116  ZombieScout::SymbolExtracter#on_sym     2.4

(See what I meant about callbacks and false-positives?)

Or you can run it on a given file or glob:

dan@aleph:~/projects/zombie_scout$ zombie_scout scout lib/app.rb
Scouted 1 methods in 1 files, in 0.041942649 seconds.
Found 0 potential zombies, with a combined flog score of 0.0.

ZombieScout will also report in CSV, if you like:

dan@aleph:~/projects/zombie_scout$ zombie_scout scout --format csv
location,name,flog_score
lib/zombie_scout/parser.rb:45,ZombieScout::Parser#on_send,8.3
lib/zombie_scout/parser.rb:17,ZombieScout::Parser#on_class,7.9
lib/zombie_scout/parser.rb:25,ZombieScout::Parser#on_module,7.2
lib/zombie_scout/parser.rb:39,ZombieScout::Parser#on_defs,5.9
lib/zombie_scout/parser.rb:81,ZombieScout::Parser#handle_def_delegators,5.8
lib/zombie_scout/parser.rb:72,ZombieScout::Parser#handle_attr_accessor,5.6
lib/zombie_scout/parser.rb:33,ZombieScout::Parser#on_def,4.9
lib/zombie_scout/parser.rb:56,ZombieScout::Parser#handle_attr_reader,4.3
lib/zombie_scout/parser.rb:64,ZombieScout::Parser#handle_attr_writer,4.3
lib/zombie_scout/parser.rb:89,ZombieScout::Parser#handle_def_delegator,3.8
lib/zombie_scout/parser.rb:95,ZombieScout::Parser#handle_scope,3.8
lib/zombie_scout/parser.rb:122,ZombieScout::ConstExtracter#on_const,2.7
lib/zombie_scout/parser.rb:116,ZombieScout::SymbolExtracter#on_sym,2.4

In Ruby

You can also embed ZombieScout in your own code, if you need that kind of thing:

irb> require 'zombie_scout'
 => true
irb> require 'pp'
 => true
irb> > pp ZombieScout::Mission.new('.').scout
[{:location=>"./lib/zombie_scout/parser.rb:17",
  :file_path=>"./lib/zombie_scout/parser.rb",
  :name=>:on_class,
  :full_name=>"ZombieScout::Parser#on_class",
  :flog_score=>7.9},
 {:location=>"./lib/zombie_scout/parser.rb:25",
  :file_path=>"./lib/zombie_scout/parser.rb",
  :name=>:on_module,
  :full_name=>"ZombieScout::Parser#on_module",
  :flog_score=>7.2},
 {:location=>"./lib/zombie_scout/parser.rb:33",
  :file_path=>"./lib/zombie_scout/parser.rb",
  :name=>:on_def,
  :full_name=>"ZombieScout::Parser#on_def",
  :flog_score=>4.9}, ...]

Code Status

• 
• 

TODOs

• parse for attr_reader/writer/accessors, & forwardables, & rails scopes
• parse for rails delegators
• let users configure: files to search for methods, files to search for calls...probably in .zombie_scout.
• option for CSV output
• if 2 classes have a method w/ the same name, you can't tell (right now, easily) whether it's dead - so don't grep for it.
• look for db/schema.rb & db/structure.sql, parse out columns, & look for those.

ToThinkAbouts:

• extract a hash-y report structure that can be used by whatever, from the default report
• pass a ruby file, or a glob
• rspec/mini-test drop-in tests that can be added easily, to fail your build if the scout or spy finds dead code. (This is probably a bad idea.)

Have ZombieScout make a hash-y report, & feed it to ZombieSpy, so the Spy knows where to focus.