Remove abbrev dependency (#419)

Our use of the `abbrev` gem is simple enough that we can replace it with
our own simple implementation. This eliminates the gem dependency so
that tomo can continue to have "minimal dependencies", as advertised in
the README.

lib/tomo/cli.rb

@@ -1,5 +1,3 @@
-require "abbrev"
-
 module Tomo
   class CLI
     autoload :Command, "tomo/cli/command"
@@ -63,14 +61,21 @@ def lookup_command(argv)
       commands = COMMANDS.merge(COMMAND_ALIASES)
 
       command_name = argv.first unless Completions.active? && argv.length == 1
-      command_name = Abbrev.abbrev(commands.keys)[command_name]
+      command_name = expand_abbrev(commands.keys, command_name)
       argv.shift if command_name
 
       command_name = "run" if command_name.nil? && task_format?(argv.first)
       command = commands[command_name] || Tomo::Commands::Default
       [command, command_name]
     end
 
+    def expand_abbrev(names, abbrev)
+      return nil if abbrev.to_s.empty?
+
+      matches = names.select { |name| name.start_with?(abbrev) }
+      matches.first if matches.one?
+    end
+
     def task_format?(arg)
       arg.to_s.match?(/\A\S+:\S*\z/)
     end

test/tomo/cli_test.rb

@@ -11,6 +11,14 @@ def test_execute_task_with_implicit_run_command
     assert_match "Simulated bundler:install", @tester.stdout
   end
 
+  def test_commands_can_be_abbreviated
+    stdout, = capture_io { @tester.run "i", "--help" }
+    assert_match "Usage: tomo init", stdout
+
+    stdout, = capture_io { @tester.run "d", "--help" }
+    assert_match "Usage: tomo deploy", stdout
+  end
+
   def test_dash_t_is_alias_for_tasks
     @tester.run "init"
     @tester.run "-T"

tomo.gemspec

@@ -31,6 +31,4 @@ Gem::Specification.new do |spec|
   spec.bindir = "exe"
   spec.executables = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
-
-  spec.add_dependency "abbrev"
 end