Add support for non-master default branch names (including main)

This change is backward-compatible by using `git` at the command line
to determine the default branch name for the current repo.

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    git-utils (2.1.0)
+    git-utils (2.2.0)
 
 GEM
   remote: https://rubygems.org/

README.md

@@ -12,17 +12,17 @@ See below for more details on the commands defined by `git-utils`. To learn more
 
 * `git amend`: alias for `git commit --amend`
 * `git bump`: makes a commit with the message `"Bump version number"`
-* `git cleanup`: deletes every branch already merged into current branch (apart from `master`, `staging`, `development`, and any branches listed in `~/.git-cleanup-preserved`). Pass the `-r` option to delete remote merged branches.
-* `git merge-into-branch [branch]`: merges current branch into given branch (defaults to `master`)
+* `git cleanup`: deletes every branch already merged into current branch (apart from `master`, `main`, `staging`, `development`, and any branches listed in `~/.git-cleanup-preserved`). Pass the `-r` option to delete remote merged branches.
+* `git merge-into-branch [branch]`: merges current branch into given branch (defaults to repo's default branch)
 * `git minor`: makes a commit with the message `"Make minor changes"`
 * `git open`: opens the remote page for the repo (macOS & Linux)
 * `git polish`: makes a commit with the message `"Polish"`
 * `git pull-request`: pushes the branch and opens the remote page for issuing a new a pull request (macOS-only)
 * `git push-branch`: pushes the current branch up to origin
 * `git delete-remote-branch <branch>`: deletes the remote branch if it is safe to do so
 * `git switch <pattern>`: switches to the first branch matching the given pattern
-* `git sync [branch]`: syncs the given branch with the remote branch (defaults to master)
-* `git sync-fork`: syncs the `master` branch of a fork with the original upstream `master` (assumes upstream configuration as in “[Configuring a remote for a fork](https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/configuring-a-remote-for-a-fork)”)
+* `git sync [branch]`: syncs the given branch with the remote branch (defaults to repo's default branch)
+* `git sync-fork`: syncs the default branch of a fork with the original upstream default (assumes upstream configuration as in “[Configuring a remote for a fork](https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/configuring-a-remote-for-a-fork)”)
 * `git typo`: makes a commit with the message `"Fix typo"`
 * `git undo`: undoes the last commit
 * `git graph`: displays full repository history in graphical format; alias for `git log --graph --oneline --decorate --all --full-history --author-date-order --no-notes`
@@ -41,9 +41,9 @@ Some of these commands deserve further explanation.
 
 ### git merge-into-branch
 
-`git merge-into-branch [target]` merges the current branch into the target branch (defaults to `master`). On a branch called `add-markdown-support`, `git merge-into-branch` is equivalent to the following:
+`git merge-into-branch [target]` merges the current branch into the target branch (defaults to repo's default branch). On a branch called `add-markdown-support` in a repo with default branch `main`, `git merge-into-branch` is equivalent to the following:
 
-    $ git checkout master
+    $ git checkout main
     $ git merge --no-ff --log add-markdown-support
 
 Note that this effectively changes the default merge behavior from fast-forward to no-fast-forward, which makes it possible to use `git log` to see which of the commit objects together have implemented a feature on a particular branch. As noted in [A successful Git branching model](http://nvie.com/posts/a-successful-git-branching-model/):
@@ -66,16 +66,16 @@ These options can be overriden (and thus restored to their defaults) by passing
 
 ### git sync
 
-`git sync [branch]` syncs the given local branch  with the remote branch (defaults to master). On a branch called `add-markdown-support`, `git sync` is equivalent to the following:
+`git sync [branch]` syncs the given local branch  with the remote branch (defaults to repo's default branch). On a branch called `add-markdown-support` in a repo with default branch `master`, `git sync` is equivalent to the following:
 
     $ git checkout master
     $ git pull
     $ git checkout add-markdown-support
 
-The main purpose of `git sync` is to prepare the current branch for merging with `master`:
+The main purpose of `git sync` is to prepare the current branch for merging with the default branch:
 
     $ git sync
-    $ git merge master
+    $ git merge master    # or `main`, etc.
 
 (This is essentially equivalent to
 

bin/git-cleanup

@@ -2,9 +2,9 @@
 require 'optparse'
 
 # Deletes (almost) every branch already merged into current branch.
-# Exceptions are `master`, `staging`, and `development`, and the current
-# branch, which are preserved. We also support custom configuration via the
-# `~/.git-cleanup-preserved` file.
+# Exceptions are `master`, `main`, `staging`, and `development`,
+# and the current branch, which are preserved.
+# We also support custom configuration via the `~/.git-cleanup-preserved` file.
 
 options = {}
 OptionParser.new do |opts|
@@ -15,7 +15,7 @@ OptionParser.new do |opts|
   end
 end.parse!
 
-preserved = "master|staging|development"
+preserved = "master|main|staging|development"
 preserved_file = File.join(Dir.home, '.git-cleanup-preserved')
 if File.exist?(preserved_file)
   additional_preserved = File.read(preserved_file).strip.split("\n")

lib/git-utils/command.rb

@@ -26,6 +26,12 @@ def current_branch
     @current_branch ||= `git rev-parse --abbrev-ref HEAD`.strip
   end
 
+  # Returns the default branch for the current repository.
+  def default_branch
+    @default_branch ||= `git symbolic-ref refs/remotes/origin/HEAD \
+     | sed 's@^refs/remotes/origin/@@'`.strip
+  end
+
   # Returns the URL for the remote origin.
   def origin_url
     @origin_url ||= `git config --get remote.origin.url`.strip
@@ -95,4 +101,4 @@ def finish?
     def deliver?
       options.deliver
     end
-end
+end

lib/git-utils/merge_branch.rb

@@ -28,8 +28,8 @@ def cmd
 
     # Returns the name of the branch to be merged into.
     # If there is anything left in the known options after parsing,
-    # that's the merge branch. Otherwise, it's master.
+    # that's the merge branch. Otherwise, it's the default branch.
     def target_branch
-      self.known_options.first || 'master'
+      self.known_options.first || default_branch
     end
 end

lib/git-utils/sync.rb

@@ -13,10 +13,10 @@ def parser
 
   # Returns a command appropriate for executing at the command line.
   def cmd
-    branch = self.known_options.first || 'master'
+    branch = self.known_options.first || default_branch
     c = ["git checkout #{branch}"]
     c << "git pull"
     c << "git checkout #{current_branch}"
     c.join("\n")
   end
-end
+end

lib/git-utils/sync_fork.rb

@@ -4,7 +4,7 @@ class SyncFork < Command
 
   def parser
     OptionParser.new do |opts|
-      opts.banner = "Usage: git sync-fork"
+      opts.banner = "Usage: git sync-fork [default]"
       opts.on_tail("-h", "--help", "this usage guide") do
         puts opts.to_s; exit 0
       end
@@ -13,9 +13,9 @@ def parser
 
   # Returns a command appropriate for executing at the command line.
   def cmd
-    c = ["git checkout master"]
+    c = ["git checkout #{default_branch}"]
     c << "git fetch upstream"
-    c << "git merge upstream/master"
+    c << "git merge upstream/#{default_branch}"
     c.join("\n")
   end
 end

lib/git-utils/version.rb

@@ -1,5 +1,5 @@
 module Git
   module Utils
-    VERSION = "2.1.0"
+    VERSION = "2.2.0"
   end
 end

spec/commands/merge_branch_spec.rb

@@ -3,7 +3,7 @@
 describe MergeBranch do
 
   let(:command) { MergeBranch.new }
-  before { command.stub(:current_branch).and_return('tau-manifesto') }
+  before  { command.stub(:current_branch).and_return('tau-manifesto') }
   subject { command }
 
   its(:cmd) { should match /git merge/ }
@@ -19,6 +19,21 @@
     its(:cmd) { should match /git checkout master/ }
   end
 
+  describe "default branch" do
+    let(:command) { MergeBranch.new }
+
+    describe "for current real repo" do
+      subject { command.default_branch }
+      it { should match 'master' }
+    end
+
+    describe "for repo with different default" do
+      before  { command.stub(:default_branch).and_return('main') }
+      subject { command.default_branch }
+      it { should match 'main' }
+    end
+  end
+
   describe "with a custom development branch" do
     let(:command) { MergeBranch.new(['development']) }
     its(:cmd) { should match /git checkout development/ }