Generator can show diff on file collision to help you decide whether to skip...

Generator can show diff on file collision to help you decide whether to skip or overwrite. Closes #6364.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@5397 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

railties/CHANGELOG

 *SVN*
 
+* Generator can show diff on file collision to help you decide whether to skip or overwrite.  #6364 [jeffw, Jeremy Kemper]
+
 * Generated directories are recursively svn added, like mkdir -p.  #6416 [NeilW]
 
 * resource and scaffold_resource generators add a restful route to config/routes.rb  [Jeremy Kemper]

railties/lib/rails_generator/commands.rb

 require 'delegate'
 require 'optparse'
 require 'fileutils'
+require 'tempfile'
 require 'erb'
 
 module Rails
@@ -91,9 +92,17 @@ def gsub_file(relative_destination, regexp, *args, &block)
 
         private
           # Ask the user interactively whether to force collision.
-          def force_file_collision?(destination)
-            $stdout.print "overwrite #{destination}? [Ynaq] "
+          def force_file_collision?(destination, src, dst, file_options = {}, &block)
+            $stdout.print "overwrite #{destination}? [Ynaqd] "
             case $stdin.gets
+              when /d/i
+                Tempfile.open(File.basename(destination), File.dirname(destination)) do |temp|
+                  temp.write render_file(src, file_options, &block)
+                  temp.rewind
+                  $stdout.puts `#{diff_cmd} #{dst} #{temp.path}`
+                end
+                puts "retrying"
+                raise 'retry diff'
               when /a/i
                 $stdout.puts "forcing #{spec.name}"
                 options[:collision] = :force
@@ -107,6 +116,10 @@ def force_file_collision?(destination)
             retry
           end
 
+          def diff_cmd
+            ENV['RAILS_DIFF'] || 'diff -u'
+          end
+
           def render_template_part(template_options)
             # Getting Sandbox to evaluate part template in it
             part_binding = template_options[:sandbox].call.sandbox_binding
@@ -197,7 +210,7 @@ def file(relative_source, relative_destination, file_options = {}, &block)
             # Make a choice whether to overwrite the file.  :force and
             # :skip already have their mind made up, but give :ask a shot.
             choice = case (file_options[:collision] || options[:collision]).to_sym #|| :ask
-              when :ask   then force_file_collision?(relative_destination)
+              when :ask   then force_file_collision?(relative_destination, source, destination, file_options, &block)
               when :force then :force
               when :skip  then :skip
               else raise "Invalid collision option: #{options[:collision].inspect}"
@@ -223,27 +236,15 @@ def file(relative_source, relative_destination, file_options = {}, &block)
           # if block given so templaters may render the source file.  If a
           # shebang is requested, replace the existing shebang or insert a
           # new one.
-          File.open(destination, 'wb') do |df|
-            File.open(source, 'rb') do |sf|
-              if block_given?
-                df.write(yield(sf))
-              else
-                if file_options[:shebang]
-                  df.puts("#!#{file_options[:shebang]}")
-                  if line = sf.gets
-                    df.puts(line) if line !~ /^#!/
-                  end
-                end
-                df.write(sf.read)
-              end
-            end
+          File.open(destination, 'wb') do |dest|
+            dest.write render_file(source, file_options, &block)
           end
 
           # Optionally change permissions.
           if file_options[:chmod]
             FileUtils.chmod(file_options[:chmod], destination)
           end
-          
+
           # Optionally add file to subversion
           system("svn add #{destination}") if options[:svn]
         end
@@ -347,6 +348,23 @@ def route_resources(*resources)
         end
 
         private
+          def render_file(path, options = {})
+            File.open(path, 'rb') do |file|
+              if block_given?
+                yield file
+              else
+                content = ''
+                if shebang = options[:shebang]
+                  content << "#!#{shebang}\n"
+                  if line = file.gets
+                    content << "line\n" if line !~ /^#!/
+                  end
+                end
+                content << file.read
+              end
+            end
+          end
+
           # Raise a usage error with an informative WordNet suggestion.
           # Thanks to Florian Gross (flgr).
           def raise_class_collision(class_name)