support THOR_MERGE values with arguments

lib/thor/shell/basic.rb

@@ -311,13 +311,11 @@ def file_collision_help(block_given) #:nodoc:
       end
 
       def show_diff(destination, content) #:nodoc:
-        diff_cmd = ENV["THOR_DIFF"] || ENV["RAILS_DIFF"] || "diff -u"
-
         require "tempfile"
         Tempfile.open(File.basename(destination), File.dirname(destination), binmode: true) do |temp|
           temp.write content
           temp.rewind
-          system %(#{diff_cmd} "#{destination}" "#{temp.path}")
+          system(*diff_tool, destination, temp.path)
         end
       end
 
@@ -372,12 +370,22 @@ def merge(destination, content) #:nodoc:
         Tempfile.open([File.basename(destination), File.extname(destination)], File.dirname(destination)) do |temp|
           temp.write content
           temp.rewind
-          system(merge_tool, temp.path, destination)
+          system(*merge_tool, temp.path, destination)
         end
       end
 
       def merge_tool #:nodoc:
-        @merge_tool ||= ENV["THOR_MERGE"] || "git difftool --no-index"
+        @merge_tool ||= begin
+          require "shellwords"
+          Shellwords.split(ENV["THOR_MERGE"] || "git difftool --no-index")
+        end
+      end
+
+      def diff_tool #:nodoc:
+        @diff_cmd ||= begin
+          require "shellwords"
+          Shellwords.split(ENV["THOR_DIFF"] || ENV["RAILS_DIFF"] || "diff -u")
+        end
       end
     end
   end

spec/actions/create_file_spec.rb

@@ -134,7 +134,7 @@ def silence!
         it "executes the block given to show file content" do
           create_file("doc/config.rb")
           expect(Thor::LineEditor).to receive(:readline).and_return("d", "n")
-          expect(@base.shell).to receive(:system).with(/diff -u/)
+          expect(@base.shell).to receive(:system).with("diff", "-u", /doc\/config\.rb/, /doc\/config\.rb/)
           invoke!
         end
 

spec/actions/file_manipulation_spec.rb

@@ -94,7 +94,7 @@ def file
       File.write(destination, "blabla")
 
       expect(Thor::LineEditor).to receive(:readline).and_return("d", "y")
-      expect(runner.shell).to receive(:system).with(/diff -u/)
+      expect(runner.shell).to receive(:system).with("diff", "-u", /encoding_with_utf8.thor/, /encoding_with_utf8.thor/)
       action :copy_file, "encoding_with_utf8.thor"
 
       exists_and_identical?("encoding_with_utf8.thor", "encoding_with_utf8.thor")

spec/shell/basic_spec.rb

@@ -546,7 +546,7 @@ def  #456  Lanç...
       it "invokes the diff command" do
         expect(Thor::LineEditor).to receive(:readline).and_return("d")
         expect(Thor::LineEditor).to receive(:readline).and_return("n")
-        expect(shell).to receive(:system).with(/diff -u/)
+        expect(shell).to receive(:system).with("diff", "-u", "foo", /foo/)
         capture(:stdout) { shell.file_collision("foo") {} }
       end
 
@@ -564,6 +564,19 @@ def  #456  Lanç...
         capture(:stdout) { shell.file_collision("foo") {} }
       end
 
+      it "invokes the merge tool with arguments when THOR_MERGE contains them" do
+        allow(ENV).to receive(:[]).with("THOR_MERGE").and_return("nvim -d")
+        expect(Thor::LineEditor).to receive(:readline).and_return("m")
+        expect(shell).to receive(:system).with("nvim", "-d", /foo/, "foo")
+        capture(:stdout) { shell.file_collision("foo") {} }
+      end
+
+      it "invokes the merge tool with arguments when there is no THOR_MERGE" do
+        expect(Thor::LineEditor).to receive(:readline).and_return("m")
+        expect(shell).to receive(:system).with("git", "difftool", "--no-index", /foo/, "foo")
+        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")