[Config] Add #with_changes

lib/cocoapods/config.rb

@@ -24,6 +24,21 @@ module Pod
       :cache_root          => Pathname.new(Dir.home) + 'Library/Caches/CocoaPods',
     }
 
+    # Applies the given changes to the config for the duration of the given
+    # block.
+    #
+    def with_changes(changes)
+      old = {}
+      changes.keys.each do |key|
+        key = key.to_sym
+        old[key] = send(key) if respond_to?(key)
+      end
+      configure_with(changes)
+      yield if block_given?
+    ensure
+      configure_with(old)
+    end
+
     public
 
     #-------------------------------------------------------------------------#

spec/unit/config_spec.rb

@@ -45,6 +45,48 @@ module Pod
 
     #-------------------------------------------------------------------------#
 
+    describe '#with_changes' do
+      it 'doesnt raise when using an unknown key' do
+        should.not.raise { @config.with_changes(:foo_bar => false) }
+      end
+
+      it 'uses the new value inside the block' do
+        @config.verbose = true
+        called = false
+        @config.with_changes(:verbose => false) do
+          @config.should.not.be.verbose
+          called = true
+        end
+        called.should.be.true
+      end
+
+      it 'reverts to the previous value after the block' do
+        @config.verbose = true
+        @config.with_changes(:verbose => false)
+        @config.should.be.verbose
+      end
+
+      it 'reverts to the previous value even when an exception is raised' do
+        @config.verbose = true
+        should.raise do
+          @config.with_changes(:verbose => false) do
+            raise 'foo'
+          end
+        end
+        @config.should.be.verbose
+      end
+
+      it 'returns the return value of the block' do
+        @config.with_changes({}) do
+          'foo'
+        end.should == 'foo'
+
+        @config.with_changes({}).should.be.nil
+      end
+    end
+
+    #-------------------------------------------------------------------------#
+
     describe 'Paths' do
       it 'returns the working directory as the installation root if a Podfile can be found' do
         Dir.chdir(temporary_directory) do