feat: attempt to get git branch name from environment variable first …

…before running git

lib/pact_broker/client/git.rb

@@ -1,24 +1,69 @@
 require 'pact_broker/client/error'
 
- # BUILDKITE_BRANCH BUILDKITE_COMMIT https://buildkite.com/docs/pipelines/environment-variables
- # CIRCLE_BRANCH CIRCLE_SHA1 https://circleci.com/docs/2.0/env-vars/
- # TRAVIS_COMMIT TRAVIS_BRANCH - TRAVIS_PULL_REQUEST_BRANCH TRAVIS_PULL_REQUEST_SHA https://docs.travis-ci.com/user/environment-variables/
- # GIT_COMMIT GIT_BRANCH https://wiki.jenkins.io/display/JENKINS/Building+a+software+project
- # GIT_COMMIT GIT_LOCAL_BRANCH https://hudson.eclipse.org/webtools/env-vars.html/
- # APPVEYOR_REPO_COMMIT APPVEYOR_REPO_BRANCH       https://www.appveyor.com/docs/environment-variables/
- # bamboo.repository.git.branch https://confluence.atlassian.com/bamboo/bamboo-variables-289277087.html
+=begin
 
- # Keep in sync with pact-provider-verifier/lib/pact/provider_verifier/git.rb
+BUILDKITE_BRANCH BUILDKITE_COMMIT https://buildkite.com/docs/pipelines/environment-variables
+CIRCLE_BRANCH CIRCLE_SHA1 https://circleci.com/docs/2.0/env-vars/
+TRAVIS_COMMIT TRAVIS_BRANCH - TRAVIS_PULL_REQUEST_BRANCH TRAVIS_PULL_REQUEST_SHA https://docs.travis-ci.com/user/environment-variables/
+GIT_COMMIT GIT_BRANCH https://wiki.jenkins.io/display/JENKINS/Building+a+software+project
+GIT_COMMIT GIT_LOCAL_BRANCH https://hudson.eclipse.org/webtools/env-vars.html/
+APPVEYOR_REPO_COMMIT APPVEYOR_REPO_BRANCH       https://www.appveyor.com/docs/environment-variables/
+CI_COMMIT_REF_NAME https://docs.gitlab.com/ee/ci/variables/predefined_variables.html
+CI_BRANCH CI_COMMIT_ID https://documentation.codeship.com/pro/builds-and-configuration/environment-variables/
+bamboo.repository.git.branch https://confluence.atlassian.com/bamboo/bamboo-variables-289277087.html
 
+=end
+
+# Keep in sync with pact-provider-verifier/lib/pact/provider_verifier/git.rb
 module PactBroker
   module Client
     module Git
-      COMMAND = 'git rev-parse --abbrev-ref HEAD'
+      COMMAND = 'git rev-parse --abbrev-ref HEAD'.freeze
+      BRANCH_ENV_VAR_names = %w{BUILDKITE_BRANCH CIRCLE_BRANCH TRAVIS_BRANCH GIT_BRANCH GIT_LOCAL_BRANCH APPVEYOR_REPO_BRANCH CI_COMMIT_REF_NAME}.freeze
 
       def self.branch
-        `#{COMMAND}`.strip
-      rescue StandardError => e
-        raise PactBroker::Client::Error, "Could not determine current git branch using command `#{COMMAND}`. #{e.class} #{e.message}"
+        find_branch_from_env_vars || branch_from_git_command
+      end
+
+      # private
+
+      def self.find_branch_from_env_vars
+        BRANCH_ENV_VAR_names.collect { |env_var_name| branch_from_env_var(env_var_name) }.compact.first
+      end
+
+      def self.branch_from_env_var(env_var_name)
+        val = ENV[env_var_name]
+        if val && val.strip.size > 0
+          val
+        else
+          nil
+        end
+      end
+
+      def self.branch_from_git_command
+        branch_name = nil
+        begin
+          branch_name = execute_git_command.strip
+        rescue StandardError => e
+          raise PactBroker::Client::Error, "Could not determine current git branch using command `#{COMMAND}`. #{e.class} #{e.message}"
+        end
+
+        validate_branch_name(branch_name)
+        branch_name
+      end
+
+      def self.validate_branch_name(branch_name)
+        if !branch_name || branch_name.size == 0
+          raise PactBroker::Client::Error, "Command `#{COMMAND}` returned an empty string when trying to determine the git branch name. This is most likely not the value you want. You will need to get the branch name another way."
+        end
+
+        if branch_name == "HEAD"
+          raise PactBroker::Client::Error, "Command `#{COMMAND}` returned 'HEAD' when trying to determine the git branch name. This is probably because the repository is in detatched HEAD state. HEAD is most likely not the value you want. You will need to get the branch name another way."
+        end
+      end
+
+      def self.execute_git_command
+        `#{COMMAND}`
       end
     end
   end

spec/lib/pact_broker/client/git_spec.rb

@@ -0,0 +1,62 @@
+require 'pact_broker/client/git'
+
+module PactBroker
+  module Client
+    module Git
+      describe ".branch" do
+        before do
+          allow(ENV).to receive(:[]).and_call_original
+        end
+
+        subject { Git.branch }
+
+        context "when there is a known environment variable for the branch" do
+          before do
+            allow(ENV).to receive(:[]).with("BUILDKITE_BRANCH").and_return("")
+            allow(ENV).to receive(:[]).with("TRAVIS_BRANCH").and_return("foo")
+          end
+
+          it "returns the value of the environment variable" do
+            expect(subject).to eq "foo"
+          end
+        end
+
+        context "when there is no known environment variable for the branch" do
+          it "attempts to execute a git command to determine the value" do
+            expect { subject }.to_not raise_error
+          end
+        end
+
+        context "when the git branch name comes back as HEAD" do
+          before do
+            allow(Git).to receive(:execute_git_command).and_return("HEAD")
+          end
+
+          it "raises an error" do
+            expect { subject }.to raise_error PactBroker::Client::Error, /returned 'HEAD'/
+          end
+        end
+
+        context "when the git branch name comes back as an empty string" do
+          before do
+            allow(Git).to receive(:execute_git_command).and_return("")
+          end
+
+          it "raises an error" do
+            expect { subject }.to raise_error PactBroker::Client::Error, /an empty string/
+          end
+        end
+
+        context "when there is an error executing the git command" do
+          before do
+            allow(Git).to receive(:execute_git_command).and_raise("some error")
+          end
+
+          it "raises an error" do
+            expect { subject }.to raise_error PactBroker::Client::Error, /some error/
+          end
+        end
+      end
+    end
+  end
+end