Avoid double outputs clear on file changes

lib/guard.rb

@@ -47,7 +47,7 @@ def setup(options = {})
       @runner     = Runner.new
       @allow_stop = Listen::Turnstile.new
 
-      UI.clear
+      UI.clear(force: true)
       deprecated_options_warning
 
       setup_groups
@@ -180,7 +180,7 @@ def stop
     #
     def reload(scopes)
       within_preserved_state do
-        UI.clear
+        UI.clear(force: true)
         UI.action_with_scopes('Reload', scopes)
         Dsl.reevaluate_guardfile if scopes.empty?
         runner.run(:reload, scopes)
@@ -193,7 +193,7 @@ def reload(scopes)
     #
     def run_all(scopes)
       within_preserved_state do
-        UI.clear
+        UI.clear(force: true)
         UI.action_with_scopes('Run', scopes)
         runner.run(:run_all, scopes)
       end

lib/guard/runner.rb

@@ -60,6 +60,7 @@ def run(task, scopes = {})
     # @param [Array<String>] removed the removed paths.
     #
     def run_on_changes(modified, added, removed)
+      UI.clearable
       scoped_guards do |guard|
         modified_paths = Watcher.match_files(guard, modified)
         added_paths    = Watcher.match_files(guard, added)

lib/guard/ui.rb

@@ -78,10 +78,19 @@ def reset_line
         STDERR.print(color_enabled? ? "\r\e[0m" : "\r\n")
       end
 
-      # Clear the output.
+      # Clear the output if clearable.
       #
-      def clear
-        system('clear;') if ::Guard.options[:clear]
+      def clear(options = {})
+        if ::Guard.options[:clear] && (@clearable || options[:force])
+          @clearable = false
+          system('clear;')
+        end
+      end
+
+      # Allow the screen to be cleared again.
+      #
+      def clearable
+        @clearable = true
       end
 
       # Show a scoped action message.

spec/guard/runner_spec.rb

@@ -125,6 +125,11 @@ class ::Guard::Bar2 < ::Guard::Guard; end
       watcher_module.stub(:match_files) { [] }
     }
 
+    it "always calls UI.clearable" do
+      Guard::UI.should_receive(:clearable)
+      subject.run_on_changes(*changes)
+    end
+
     context 'when clearable' do
       before { subject.stub(:clearable?) { true } }
 

spec/guard/ui_spec.rb

@@ -0,0 +1,40 @@
+require 'spec_helper'
+
+describe Guard::UI do
+
+  describe "clear" do
+    context "Guard.options[:clear] is true" do
+      before { ::Guard.stub(:options) { { clear: true } } }
+
+      it "clears the outputs if clearable" do
+        Guard::UI.clearable
+        Guard::UI.should_receive(:system).with('clear;')
+        Guard::UI.clear
+      end
+
+      it "doesn't clear the output if already cleared" do
+        Guard::UI.stub(:system)
+        Guard::UI.clear
+        Guard::UI.should_not_receive(:system).with('clear;')
+        Guard::UI.clear
+      end
+
+      it "clears the outputs if forced" do
+        Guard::UI.stub(:system)
+        Guard::UI.clear
+        Guard::UI.should_receive(:system).with('clear;')
+        Guard::UI.clear(force: true)
+      end
+    end
+
+    context "Guard.options[:clear] is false" do
+      before { ::Guard.stub(:options) { { clear: false } } }
+
+      it "doesn't clear the output" do
+        Guard::UI.should_not_receive(:system).with('clear;')
+        Guard::UI.clear
+      end
+    end
+  end
+
+end