Add check to make sure file exists before inject

Author: vcavallo

lib/thor/actions/inject_into_file.rb

@@ -1,4 +1,5 @@
 require "thor/actions/empty_directory"
+require "pry"
 
 class Thor
   module Actions
@@ -56,7 +57,11 @@ def invoke!
           replacement + '\0'
         end
 
-        replace!(/#{flag}/, content, config[:force])
+        if File.exist?(destination)
+          replace!(/#{flag}/, content, config[:force])
+        else
+          raise MalformattedArgumentError, "The file #{ destination } does not appear to exist"
+        end
       end
 
       def revoke!

spec/actions/inject_into_file_spec.rb

@@ -70,6 +70,21 @@ def file
       expect(File.read(file)).to eq("__start__\nREADME\nmore content\n__end__\n")
     end
 
+    it "does not attempt to change the file if it doesn't exist" do
+      expect_any_instance_of(Thor::Actions::InjectIntoFile).not_to receive(:replace!)
+      invoker.inject_into_file "idontexist", :before => "something" do
+        "any content"
+      end rescue nil
+    end
+
+    it "raises a malformatted argument error including filename if file doesn't exist" do
+      expect do
+        invoker.inject_into_file "idontexist", :before => "something" do
+          "any content"
+        end
+      end.to raise_error(Thor::MalformattedArgumentError, /does not appear to exist/)
+    end
+
     it "does change the file if already includes content and :force is true" do
       invoke! "doc/README", :before => "__end__" do
         "more content\n"