Fix bug #196 && prepare v8.0.0 release (#197)

* Fix bug #196

The call to `empty?` will fail if the key GITHUB_HEAD_REF does not exist.

Before fixing this problem, I extracted the logic to its own testable class. Then I added tests, which also showed that `GITHUB_REF_NAME` would never be returned either (a previously unknown bug) because `!@env["GITHUB_HEAD_REF"]&.empty?` will always be truthy unless the key exists and it's empty.

This would (possibly) be cleaner with pattern matching. Ruby has pattern matching but we can't use it yet due to minimum supported Ruby version https://docs.ruby-lang.org/en/3.0/syntax/pattern_matching_rdoc.html.

Close #196

* v8.0.0

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## HEAD
 
+## 8.0.0
+
 - Breaking change: Delete apps on teardown. Previously hatchet would delete apps lazily to help with debugging. This behavior allowed developers to inspect logs and `heroku run bash` in the event of an unexpected failure. In practice, it is rarely needed and causes accounts to retain apps indefinitely. Previously there was no cost to retaining applications, but now `basic` applications incur a charge. Change details:
   - The application teardown process now deletes applications directly.
   - To skip destroying applications on teardown, set `HEROKU_DEBUG_EXPENSIVE=1`. This env var will cause `App#teardown!` to skip deletion so you can introspect why one failed.

lib/hatchet.rb

@@ -21,29 +21,43 @@ module Hatchet
 require 'hatchet/init_project'
 require 'hatchet/heroku_run'
 
-module Hatchet
-  RETRIES = Integer(ENV['HATCHET_RETRIES']   || 1)
-  Runner  = Hatchet::GitApp
+class DefaultCIBranch
+  def initialize(env: ENV)
+    @env = env
+  end
 
-  def self.git_branch
+  def call
     # https://circleci.com/docs/variables
-    return ENV['CIRCLE_BRANCH'] if ENV['CIRCLE_BRANCH']
+    return @env['CIRCLE_BRANCH'] if @env['CIRCLE_BRANCH']
     # https://docs.github.com/en/actions/learn-github-actions/environment-variables
     # GITHUB_HEAD_REF is provided for PRs, but blank for branch actions.
-    return ENV['GITHUB_HEAD_REF'] if !ENV['GITHUB_HEAD_REF'].empty?
+    return @env['GITHUB_HEAD_REF'] if @env['GITHUB_HEAD_REF'] && !@env['GITHUB_HEAD_REF']&.empty?
     # GITHUB_REF_NAME is incorrect on PRs (`1371/merge`), but correct for branch actions.
-    return ENV['GITHUB_REF_NAME'] if ENV['GITHUB_REF_NAME']
+    return @env['GITHUB_REF_NAME'] if @env['GITHUB_REF_NAME']
     # https://devcenter.heroku.com/articles/heroku-ci#immutable-environment-variables
-    return ENV['HEROKU_TEST_RUN_BRANCH'] if ENV['HEROKU_TEST_RUN_BRANCH']
+    return @env['HEROKU_TEST_RUN_BRANCH'] if @env['HEROKU_TEST_RUN_BRANCH']
     # TRAVIS_BRANCH works fine unless the build is a pull-request. In that case, it will contain the target branch
     # not the actual pull-request branch! TRAVIS_PULL_REQUEST_BRANCH contains the correct branch but will be empty
     # for push builds. See: https://docs.travis-ci.com/user/environment-variables/
-    return ENV['TRAVIS_PULL_REQUEST_BRANCH'] if ENV['TRAVIS_PULL_REQUEST_BRANCH'] && !ENV['TRAVIS_PULL_REQUEST_BRANCH'].empty?
-    return ENV['TRAVIS_BRANCH'] if ENV['TRAVIS_BRANCH']
+    return @env['TRAVIS_PULL_REQUEST_BRANCH'] if @env['TRAVIS_PULL_REQUEST_BRANCH'] && !@env['TRAVIS_PULL_REQUEST_BRANCH']&.empty?
+    return @env['TRAVIS_BRANCH'] if @env['TRAVIS_BRANCH']
+  end
+end
 
-    out = `git rev-parse --abbrev-ref HEAD`.strip
-    raise "Attempting to find current branch name. Error: Cannot describe git: #{out}" unless $?.success?
-    out
+module Hatchet
+  RETRIES = Integer(ENV['HATCHET_RETRIES']   || 1)
+  Runner  = Hatchet::GitApp
+
+  def self.git_branch
+    branch = DefaultCIBranch.new.call
+
+    if branch
+      branch
+    else
+      out = `git rev-parse --abbrev-ref HEAD`.strip
+      raise "Attempting to find current branch name. Error: Cannot describe git: #{out}" unless $?.success?
+      out
+    end
   end
 
   if ENV["HATCHET_DEBUG_DEADLOCK"]

lib/hatchet/version.rb

@@ -1,3 +1,3 @@
 module Hatchet
-  VERSION = "7.4.0"
+  VERSION = "8.0.0"
 end

spec/unit/default_ci_branch_spec.rb

@@ -0,0 +1,27 @@
+
+require "spec_helper"
+
+describe "DefaultCIBranch" do
+  it "doesn't error on empty env" do
+    out = DefaultCIBranch.new(env: {}).call
+    expect(out).to be_nil
+  end
+
+  it "GitHub PRs" do
+    out = DefaultCIBranch.new(env: {"GITHUB_HEAD_REF" => "iAmaPR"}).call
+    expect(out).to eq("iAmaPR")
+
+    out = DefaultCIBranch.new(env: {"GITHUB_HEAD_REF" => ""}).call
+    expect(out).to be_nil
+  end
+
+  it "GitHub branches" do
+    out = DefaultCIBranch.new(env: {"GITHUB_REF_NAME" => "iAmaBranch"}).call
+    expect(out).to eq("iAmaBranch")
+  end
+
+  it "heroku" do
+    out = DefaultCIBranch.new(env: {"HEROKU_TEST_RUN_BRANCH" => "iAmaBranch"}).call
+    expect(out).to eq("iAmaBranch")
+  end
+end