Add command_exists? method to Thor and Thor::Group classes

lib/thor.rb

@@ -439,6 +439,17 @@ def disable_required_check?(command) #:nodoc:
       command && disable_required_check.include?(command.name.to_sym)
     end
 
+    # Checks if a specified command exists.
+    #
+    # ==== Parameters
+    # command_name<String>:: The name of the command to check for existence.
+    #
+    # ==== Returns
+    # Boolean:: +true+ if the command exists, +false+ otherwise.
+    def command_exists?(command_name) #:nodoc:
+      commands.keys.include?(normalize_command_name(command_name))
+    end
+
   protected
 
     # Returns this class exclusive options array set.

lib/thor/group.rb

@@ -211,6 +211,17 @@ def handle_argument_error(command, error, _args, arity) #:nodoc:
       raise error, msg
     end
 
+    # Checks if a specified command exists.
+    #
+    # ==== Parameters
+    # command_name<String>:: The name of the command to check for existence.
+    #
+    # ==== Returns
+    # Boolean:: +true+ if the command exists, +false+ otherwise.
+    def command_exists?(command_name) #:nodoc:
+      commands.keys.include?(command_name)
+    end
+
   protected
 
     # The method responsible for dispatching given the args.

spec/fixtures/script.thor

@@ -264,12 +264,15 @@ end
 class Apple < Thor
   namespace :fruits
   desc 'apple', 'apple'; def apple; end
+  desc 'rotten-apple', 'rotten apple'; def rotten_apple; end
+  map "ra" => :rotten_apple
 end
 
 class Pear < Thor
   namespace :fruits
   desc 'pear', 'pear'; def pear; end
 end
+
 class MyClassOptionScript < Thor
   class_option :free
 

spec/group_spec.rb

@@ -186,6 +186,16 @@
     end
   end
 
+  describe "#command_exists?" do
+    it "returns true for a command that is defined in the class" do
+      expect(MyCounter.command_exists?("one")).to be true
+    end
+
+    it "returns false for a command that is not defined in the class" do
+      expect(MyCounter.command_exists?("zero")).to be false
+    end
+  end
+
   describe "edge-cases" do
     it "can handle boolean options followed by arguments" do
       klass = Class.new(Thor::Group) do

spec/thor_spec.rb

@@ -340,6 +340,18 @@ def self.exit_on_failure?
     end
   end
 
+  describe "#command_exists?" do
+    it "returns true for a command that is defined in the class" do
+      expect(MyScript.command_exists?("zoo")).to be true
+      expect(MyScript.command_exists?("name-with-dashes")).to be true
+      expect(MyScript.command_exists?("animal_prison")).to be true
+    end
+
+    it "returns false for a command that is not defined in the class" do
+      expect(MyScript.command_exists?("animal_heaven")).to be false
+    end
+  end
+
   describe "#map" do
     it "calls the alias of a method if one is provided" do
       expect(MyScript.start(%w(-T fish))).to eq(%w(fish))