Use git push --force during promotion

lib/build_strategies/production_build_strategy.rb

@@ -7,9 +7,14 @@ class << self
     # The primary function of promote_build is to update the branches specified
     # in on_green_update field of Repository.
     #
-    # A feature of promote build is that it will not cause the promotion ref to move
-    # backwards. For instance, if build 1 finishes after build 2, we don't cause the promotion ref to move
-    # backwards by overwriting promotion_ref with build 1
+    # A feature of promote_build is that it will not cause the promotion ref to
+    # move backwards. For instance, if build 1 finishes after build 2, we don't
+    # cause the promotion ref to move backwards by overwriting promotion_ref
+    # with build 1
+    #
+    # promote_build does use a force push in order to overwrite experimental
+    # branches that may have been manually placed on the promotion ref by a
+    # developer for testing.
     def promote_build(build_ref, repository)
       repository.promotion_refs.each do |promotion_ref|
         unless included_in_promotion_ref?(build_ref, promotion_ref)
@@ -44,22 +49,18 @@ def merge_ref(build)
     end
 
     def update_branch(branch_name, ref_to_promote)
-      Cocaine::CommandLine.new("git push", "origin #{ref_to_promote}:refs/heads/#{branch_name}").run
+      Cocaine::CommandLine.new("git push", "--force origin #{ref_to_promote}:refs/heads/#{branch_name}").run
     end
 
   private
 
     def included_in_promotion_ref?(build_ref, promotion_ref)
-      return unless ref_exists?(promotion_ref)
-
-      cherry_cmd = Cocaine::CommandLine.new("git cherry", "origin/#{promotion_ref} #{build_ref}")
-      cherry_cmd.run.lines.count == 0
+      # --is-ancestor was added in git 1.8.0
+      # exit ->   1: not an ancestor
+      # exit -> 128: the commit does not exist
+      ancestor_cmd = Cocaine::CommandLine.new("git merge-base", "--is-ancestor #{build_ref} origin/#{promotion_ref}", :expected_outcodes => [0, 1, 128])
+      ancestor_cmd.run
+      ancestor_cmd.exit_status == 0
     end
-
-    def ref_exists?(promotion_ref)
-      show_ref = Cocaine::CommandLine.new("git show-ref", promotion_ref, :expected_outcodes => [0,1])
-      show_ref.run.present?
-    end
-
   end
 end

spec/lib/build_strategies/production_build_strategy_spec.rb

@@ -38,30 +38,21 @@
   describe "#promote_build" do
     subject { described_class.promote_build(build.ref, project.repository) }
 
-    context "when pushing to a ref that doesn't exist" do
+    context "when the ref is an ancestor" do
       before(:each) {
-        mock_show_ref_command = double
-        expect(mock_show_ref_command).to receive(:run).and_return "deadbeef refs/remote/origin/branch"
-        allow(Cocaine::CommandLine).to receive(:new).with("git show-ref", anything, anything).and_return mock_show_ref_command
-
-        mock_cherry_command = double
-        expect(mock_cherry_command).to receive(:run).and_return "+ deadbeef"
-        allow(Cocaine::CommandLine).to receive(:new).with("git cherry", "origin/#{project.repository.promotion_refs.first} #{build.ref}").and_return mock_cherry_command
+        expect(described_class).to receive(:included_in_promotion_ref?).and_return(true)
       }
-      it "pushes the ref" do
-        expect(described_class).to receive(:update_branch).with(project.repository.promotion_refs.first, build.ref)
+      it "does not perform an update" do
+        expect(described_class).to_not receive(:update_branch)
         subject
       end
     end
 
-    context "when pushing to a ref that doesn't exist" do
+    context "when the ref is not an ancestor" do
       before(:each) {
-        mock_git_command = double
-        expect(mock_git_command).to receive(:run).and_return ""
-        allow(Cocaine::CommandLine).to receive(:new).with("git show-ref", anything, anything).and_return mock_git_command
+        expect(described_class).to receive(:included_in_promotion_ref?).and_return(false)
       }
-
-      it "fails gracefully if the ref is undefined" do
+      it "should update the promotion branch" do
         expect(described_class).to receive(:update_branch).with(project.repository.promotion_refs.first, build.ref)
         subject
       end
@@ -76,7 +67,7 @@
     it "should promote a sha" do
       mock_git_command = double
       expect(mock_git_command).to receive(:run).and_return ""
-      expect(Cocaine::CommandLine).to receive(:new).with("git push", "origin abc123:refs/heads/last-green").and_return mock_git_command
+      expect(Cocaine::CommandLine).to receive(:new).with("git push", "--force origin abc123:refs/heads/last-green").and_return mock_git_command
 
       subject
     end