Add merge action to file colision menu

Currently, if want to reflect the changed contents, only have to grasp the
contents of diff and reflect it manually later or overwrite once to check
the difference. This is a little inconvenient.

If merge is selected, the specified merge tool will be executed. By doing
this, can reflect changes while checking.

Merge tool is obtained from environment variables and git config.
I doubt that it is appropriate to get a value from git config, but I am
thinking that there may be useful.

lib/thor/shell/basic.rb

@@ -247,11 +247,11 @@ def print_wrapped(message, options = {})
       #
       # ==== Parameters
       # destination<String>:: the destination file to solve conflicts
-      # block<Proc>:: an optional block that returns the value to be used in diff
+      # block<Proc>:: an optional block that returns the value to be used in diff and merge
       #
       def file_collision(destination)
         return true if @always_force
-        options = block_given? ? "[Ynaqdh]" : "[Ynaqh]"
+        options = block_given? ? "[Ynaqdhm]" : "[Ynaqh]"
 
         loop do
           answer = ask(
@@ -275,6 +275,13 @@ def file_collision(destination)
           when is?(:diff)
             show_diff(destination, yield) if block_given?
             say "Retrying..."
+          when is?(:merge)
+            if block_given? && !merge_tool.empty?
+              merge(destination, yield)
+              return nil
+            end
+
+            say "Please specify merge tool to `THOR_MERGE` env."
           else
             say file_collision_help
           end
@@ -352,6 +359,7 @@ def file_collision_help #:nodoc:
         q - quit, abort
         d - diff, show the differences between the old and the new
         h - help, show this help
+        m - merge, run merge tool
         HELP
       end
 
@@ -440,6 +448,23 @@ def ask_filtered(statement, color, options)
         end
         correct_answer
       end
+
+      def merge(destination, content) #:nodoc:
+        require "tempfile"
+        Tempfile.open([File.basename(destination), File.extname(destination)], File.dirname(destination)) do |temp|
+          temp.write content
+          temp.rewind
+          system %(#{merge_tool} "#{temp.path}" "#{destination}")
+        end
+      end
+
+      def merge_tool #:nodoc:
+        @merge_tool ||= ENV["THOR_MERGE"] || git_merge_tool
+      end
+
+      def git_merge_tool #:nodoc:
+        `git config merge.tool`.rstrip rescue ""
+      end
     end
   end
 end

spec/actions/create_file_spec.rb

@@ -104,7 +104,7 @@ def silence!
         it "shows conflict status to the user" do
           file = File.join(destination_root, "doc/config.rb")
           expect(create_file("doc/config.rb")).not_to be_identical
-          expect(Thor::LineEditor).to receive(:readline).with("Overwrite #{file}? (enter \"h\" for help) [Ynaqdh] ", anything).and_return("s")
+          expect(Thor::LineEditor).to receive(:readline).with("Overwrite #{file}? (enter \"h\" for help) [Ynaqdhm] ", anything).and_return("s")
 
           content = invoke!
           expect(content).to match(%r{conflict  doc/config\.rb})
@@ -129,6 +129,14 @@ def silence!
           expect(@base.shell).to receive(:system).with(/diff -u/)
           invoke!
         end
+
+        it "executes the block given to run merge tool" do
+          create_file("doc/config.rb")
+          allow(@base.shell).to receive(:merge_tool).and_return("meld")
+          expect(Thor::LineEditor).to receive(:readline).and_return("m")
+          expect(@base.shell).to receive(:system).with(/meld/)
+          invoke!
+        end
       end
     end
 

spec/shell/basic_spec.rb

@@ -356,8 +356,8 @@ def  #456  Lanç...
     end
 
     describe "when a block is given" do
-      it "displays diff options to the user" do
-        expect(Thor::LineEditor).to receive(:readline).with('Overwrite foo? (enter "h" for help) [Ynaqdh] ', :add_to_history => false).and_return("s")
+      it "displays diff and merge options to the user" do
+        expect(Thor::LineEditor).to receive(:readline).with('Overwrite foo? (enter "h" for help) [Ynaqdhm] ', :add_to_history => false).and_return("s")
         shell.file_collision("foo") {}
       end
 
@@ -367,6 +367,28 @@ def  #456  Lanç...
         expect(shell).to receive(:system).with(/diff -u/)
         capture(:stdout) { shell.file_collision("foo") {} }
       end
+
+      it "invokes the merge tool" do
+        allow(shell).to receive(:merge_tool).and_return("meld")
+        expect(Thor::LineEditor).to receive(:readline).and_return("m")
+        expect(shell).to receive(:system).with(/meld/)
+        capture(:stdout) { shell.file_collision("foo") {} }
+      end
+
+      it "invokes the merge tool that specified at ENV['THOR_MERGE']" do
+        allow(ENV).to receive(:[]).with("THOR_MERGE").and_return("meld")
+        expect(Thor::LineEditor).to receive(:readline).and_return("m")
+        expect(shell).to receive(:system).with(/meld/)
+        capture(:stdout) { shell.file_collision("foo") {} }
+      end
+
+      it "show warning if user chooses merge but merge tool is not specified" do
+        allow(shell).to receive(:merge_tool).and_return("")
+        expect(Thor::LineEditor).to receive(:readline).and_return("m")
+        expect(Thor::LineEditor).to receive(:readline).and_return("n")
+        help = capture(:stdout) { shell.file_collision("foo") {} }
+        expect(help).to match(/Please specify merge tool to `THOR_MERGE` env/)
+      end
     end
   end
 end