tap: add methods to get git related information

These methods will be used in `brew --version`, `brew config`
and `brew doctor` after core/formula separation.

Closes Homebrew/homebrew#49796.

Signed-off-by: Xu Cheng <xucheng@me.com>

Library/Homebrew/tap.rb

@@ -83,7 +83,7 @@ class Tap
   # e.g. `https://github.com/user/homebrew-repo`
   def remote
     @remote ||= if installed?
-      if git?
+      if git? && Utils.git_available?
         path.cd do
           Utils.popen_read("git", "config", "--get", "remote.origin.url").chomp
         end
@@ -98,6 +98,34 @@ class Tap
     (path/".git").exist?
   end
 
+  # git HEAD for this {Tap}.
+  def git_head
+    raise TapUnavailableError, name unless installed?
+    return unless git? && Utils.git_available?
+    path.cd { Utils.popen_read("git", "rev-parse", "--verify", "-q", "HEAD").chuzzle }
+  end
+
+  # git HEAD in short format for this {Tap}.
+  def git_short_head
+    raise TapUnavailableError, name unless installed?
+    return unless git? && Utils.git_available?
+    path.cd { Utils.popen_read("git", "rev-parse", "--short=4", "--verify", "-q", "HEAD").chuzzle }
+  end
+
+  # time since git last commit for this {Tap}.
+  def git_last_commit
+    raise TapUnavailableError, name unless installed?
+    return unless git? && Utils.git_available?
+    path.cd { Utils.popen_read("git", "show", "-s", "--format=%cr", "HEAD").chuzzle }
+  end
+
+  # git last commit date for this {Tap}.
+  def git_last_commit_date
+    raise TapUnavailableError, name unless installed?
+    return unless git? && Utils.git_available?
+    path.cd { Utils.popen_read("git", "show", "-s", "--format=%cd", "--date=short", "HEAD").chuzzle }
+  end
+
   # The issues URL of this {Tap}.
   # e.g. `https://github.com/user/homebrew-repo/issues`
   def issues_url

Library/Homebrew/test/test_tap.rb

@@ -1,6 +1,8 @@
 require "testing_env"
 
 class TapTest < Homebrew::TestCase
+  include FileUtils
+
   def setup
     @path = Tap::TAP_DIRECTORY/"homebrew/homebrew-foo"
     @path.mkpath
@@ -16,7 +18,7 @@ class TapTest < Homebrew::TestCase
     EOS
     @alias_file = @path/"Aliases/bar"
     @alias_file.parent.mkpath
-    FileUtils.ln_s @formula_file, @alias_file
+    ln_s @formula_file, @alias_file
     (@path/"formula_renames.json").write <<-EOS.undent
      { "oldname": "foo" }
     EOS
@@ -25,14 +27,21 @@ class TapTest < Homebrew::TestCase
     EOS
     @cmd_file = @path/"cmd/brew-tap-cmd.rb"
     @cmd_file.parent.mkpath
-    FileUtils.touch @cmd_file
-    FileUtils.chmod 0755, @cmd_file
+    touch @cmd_file
+    chmod 0755, @cmd_file
     @manpage_file = @path/"man/man1/brew-tap-cmd.1"
     @manpage_file.parent.mkpath
-    FileUtils.touch @manpage_file
+    touch @manpage_file
   end
 
   def setup_git_repo
+    env = ENV.to_hash
+    %w[AUTHOR COMMITTER].each do |role|
+      ENV["GIT_#{role}_NAME"] = "brew tests"
+      ENV["GIT_#{role}_EMAIL"] = "brew-tests@localhost"
+      ENV["GIT_#{role}_DATE"] = "Thu May 21 00:04:11 2009 +0100"
+    end
+
     @path.cd do
       shutup do
         system "git", "init"
@@ -41,6 +50,8 @@ class TapTest < Homebrew::TestCase
         system "git", "commit", "-m", "init"
       end
     end
+  ensure
+    ENV.replace(env)
   end
 
   def teardown
@@ -74,7 +85,7 @@ class TapTest < Homebrew::TestCase
     t = Tap.new("someone", "foo")
     path = Tap::TAP_DIRECTORY/"someone/homebrew-foo"
     path.mkpath
-    FileUtils.cd path do
+    cd path do
       shutup { system "git", "init" }
       system "git", "remote", "add", "origin",
         "https://github.com/someone/homebrew-foo"
@@ -123,6 +134,26 @@ class TapTest < Homebrew::TestCase
     refute_predicate version_tap, :private?
   end
 
+  def test_remote_not_git_repo
+    assert_nil @tap.remote
+  end
+
+  def test_remote_git_not_available
+    setup_git_repo
+    Utils.stubs(:git_available?).returns(false)
+    assert_nil @tap.remote
+  end
+
+  def test_git_variant
+    touch @path/"README"
+    setup_git_repo
+
+    assert_equal "e1893a6bd191ba895c71b652ff8376a6114c7fa7", @tap.git_head
+    assert_equal "e189", @tap.git_short_head
+    assert_match %r{years ago}, @tap.git_last_commit
+    assert_equal "2009-05-21", @tap.git_last_commit_date
+  end
+
   def test_private_remote
     skip "HOMEBREW_GITHUB_API_TOKEN is required" unless ENV["HOMEBREW_GITHUB_API_TOKEN"]
     assert_predicate @tap, :private?
@@ -174,6 +205,8 @@ class TapTest < Homebrew::TestCase
 end
 
 class CoreFormulaRepositoryTest < Homebrew::TestCase
+  include FileUtils
+
   def setup
     @repo = CoreFormulaRepository.new
   end
@@ -204,7 +237,7 @@ class CoreFormulaRepositoryTest < Homebrew::TestCase
     EOS
     @alias_file = @repo.alias_dir/"bar"
     @alias_file.parent.mkpath
-    FileUtils.ln_s @formula_file, @alias_file
+    ln_s @formula_file, @alias_file
 
     assert_equal [@formula_file], @repo.formula_files
     assert_equal ["foo"], @repo.formula_names