Add --since CLI option for repository diff filter

[fix #262]

Changelog.md

@@ -1,5 +1,7 @@
 # v0.8.1 2015-xx-xx
 
+* Add --since flag to constrain mutated subjects based on
+  repository diff from HEAD to other REVISON.
 * Add mutation from #[] to #at / #fetch
 
 # v0.8.0 2015-06-15

config/flay.yml

@@ -1,3 +1,3 @@
 ---
 threshold: 18
-total_score: 1189
+total_score: 1196

lib/mutant/cli.rb

@@ -155,6 +155,9 @@ module Mutant
       opts.on('--ignore-subject EXPRESSION', 'Ignore subjects that match EXPRESSION as prefix') do |pattern|
         add_matcher(:ignore_expressions, config.expression_parser.(pattern))
       end
+      opts.on('--since REVISION', 'Only select subjects touched since REVISION') do |revision|
+        add_matcher(:subject_filters, Repository::SubjectFilter.new(Repository::Diff.from_head(revision)))
+      end
     end
 
     # Add debug options

spec/unit/mutant/cli_spec.rb

@@ -128,6 +128,7 @@ Options:
         --expected-coverage COVERAGE Fail unless COVERAGE is not reached exactly, parsed via Rational()
         --use INTEGRATION            Use INTEGRATION to kill mutations
         --ignore-subject EXPRESSION  Ignore subjects that match EXPRESSION as prefix
+        --since REVISION             Only select subjects touched since REVISION
         --fail-fast                  Fail fast
         --version                    Print mutants version
     -d, --debug                      Enable debugging output
@@ -230,6 +231,20 @@ Options:
       end
     end
 
+    context 'with --since flag' do
+      let(:flags) { %w[--since master] }
+
+      let(:expected_matcher_config) do
+        default_matcher_config.update(
+          subject_filters: [
+            Mutant::Repository::SubjectFilter.new(Mutant::Repository::Diff.new('HEAD', 'master'))
+          ]
+        )
+      end
+
+      it_should_behave_like 'a cli parser'
+    end
+
     context 'with subject-ignore flag' do
       let(:flags) { %w[--ignore-subject Foo::Bar] }