Honor repo default branch

features/step_definitions/git_steps.rb

@@ -22,3 +22,26 @@
   git_base: file://#{expand_path('.')}/
   CONFIG
 end
+
+Given /a remote module repository with "(.+?)" as the default branch/ do |branch| # rubocop:disable Lint/AmbiguousRegexpLiteral
+  steps %(
+    Given a directory named "sources"
+    And I run `git clone --mirror https://github.com/maestrodev/puppet-test sources/puppet-test`
+    And a file named "managed_modules.yml" with:
+      """
+      ---
+        - puppet-test
+      """
+  )
+  write_file('modulesync.yml', <<-CONFIG)
+---
+  namespace: sources
+  git_base: file://#{expand_path('.')}/
+  CONFIG
+  cd('sources/puppet-test') do
+    steps %(
+      And I run `git branch -M master #{branch}`
+      And I run `git symbolic-ref HEAD refs/heads/#{branch}`
+    )
+  end
+end

features/update.feature

@@ -885,3 +885,21 @@ Feature: update
     Then the exit status should be 0
     Then the output should not contain "error"
     Then the output should not contain "rejected"
+
+  Scenario: Repository with a default branch other than master
+    Given a mocked git configuration
+    And a remote module repository with "develop" as the default branch
+    And a file named "config_defaults.yml" with:
+      """
+      ---
+      Gemfile:
+        gem_source: https://somehost.com
+      """
+    And a directory named "moduleroot"
+    And a file named "moduleroot/Gemfile.erb" with:
+      """
+      source '<%= @configs['gem_source'] %>'
+      """
+    When I run `msync update -m "Update Gemfile"`
+    Then the exit status should be 0
+    Then the output should contain "Using repository's default branch: develop"

lib/modulesync/cli.rb

@@ -53,8 +53,8 @@ class Base < Thor
                    :desc => 'A regular expression to skip repositories.'
       class_option :branch,
                    :aliases => '-b',
-                   :desc => 'Branch name to make the changes in. Defaults to master.',
-                   :default => CLI.defaults[:branch] || 'master'
+                   :desc => 'Branch name to make the changes in. Defaults to the default branch of the upstream repository, but falls back to "master".',
+                   :default => CLI.defaults[:branch]
 
       desc 'update', 'Update the modules in managed_modules.yml'
       option :message,

lib/modulesync/git.rb

@@ -2,7 +2,7 @@
 require 'puppet_blacksmith'
 
 module ModuleSync
-  module Git
+  module Git # rubocop:disable Metrics/ModuleLength
     include Constants
 
     def self.remote_branch_exists?(repo, branch)
@@ -18,7 +18,17 @@ def self.remote_branch_differ?(repo, local_branch, remote_branch)
         repo.diff("#{local_branch}..origin/#{remote_branch}").any?
     end
 
+    def self.default_branch(repo)
+      symbolic_ref = repo.branches.find { |b| b.full =~ %r{remotes/origin/HEAD} }
+      return unless symbolic_ref
+      %r{remotes/origin/HEAD\s+->\s+origin/(?<branch>.+?)$}.match(symbolic_ref.full)[:branch]
+    end
+
     def self.switch_branch(repo, branch)
+      unless branch
+        branch = default_branch(repo)
+        puts "Using repository's default branch: #{branch}"
+      end
       return if repo.current_branch == branch
 
       if local_branch_exists?(repo, branch)
@@ -95,12 +105,19 @@ def self.tag(repo, version, tag_pattern)
       repo.push('origin', tag)
     end
 
+    def self.checkout_branch(repo, branch)
+      selected_branch = branch || repo.current_branch || 'master'
+      repo.branch(selected_branch).checkout
+      selected_branch
+    end
+    private_class_method :checkout_branch
+
     # Git add/rm, git commit, git push
     def self.update(name, files, options)
       module_root = "#{options[:project_root]}/#{name}"
       message = options[:message]
       repo = ::Git.open(module_root)
-      repo.branch(options[:branch]).checkout
+      branch = checkout_branch(repo, options[:branch])
       files.each do |file|
         if repo.status.deleted.include?(file)
           repo.remove(file)
@@ -119,11 +136,11 @@ def self.update(name, files, options)
         end
         repo.commit(message, opts_commit)
         if options[:remote_branch]
-          if remote_branch_differ?(repo, options[:branch], options[:remote_branch])
-            repo.push('origin', "#{options[:branch]}:#{options[:remote_branch]}", opts_push)
+          if remote_branch_differ?(repo, branch, options[:remote_branch])
+            repo.push('origin', "#{branch}:#{options[:remote_branch]}", opts_push)
           end
         else
-          repo.push('origin', options[:branch], opts_push)
+          repo.push('origin', branch, opts_push)
         end
         # Only bump/tag if pushing didn't fail (i.e. there were changes)
         m = Blacksmith::Modulefile.new("#{module_root}/metadata.json")
@@ -154,7 +171,7 @@ def self.update_noop(name, options)
       puts "Using no-op. Files in #{name} may be changed but will not be committed."
 
       repo = ::Git.open("#{options[:project_root]}/#{name}")
-      repo.branch(options[:branch]).checkout
+      checkout_branch(repo, options[:branch])
 
       puts 'Files changed:'
       repo.diff('HEAD', '--').each do |diff|