improve git repository detection

* configure.in (AC_CONFIG_FILES): $srcdir/.git can be a file pointing
  the real git_dir, such as when the git working tree is a "linked
  working tree" (a working tree created by git-worktree). So use
  git-rev-parse --git-dir to check if $srcdir is the top-level of a git
  repository, not just checking if the $srcdir/.git directory does exist
  or not.  [ruby-core:74759] [Bug #12239]
* tool/change_maker.rb: use tool/vcs.rb to detect VCS. This used to have
  its own VCS detection code, while we have tool/vcs.rb.
* tool/vcs.rb (detect): remove code duplication

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54468 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

2 files changed, 16 insertions, 10 deletions

diff --git a/tool/change_maker.rb b/tool/change_maker.rb
index 2bbc275d93..f7b7650a51 100755
--- a/tool/change_maker.rb
+++ b/tool/change_maker.rb
@@ -1,5 +1,8 @@
 #! ./miniruby
 
+$:.unshift(File.expand_path("../../lib", __FILE__))
+require File.expand_path("../vcs", __FILE__)
+
 def diff2index(cmd, *argv)
   lines = []
   path = nil
@@ -22,10 +25,17 @@ def diff2index(cmd, *argv)
   lines.empty? ? nil : lines
 end
 
-if `svnversion` =~ /^\d+/
+vcs = begin
+  VCS.detect(".")
+rescue VCS::NotFoundError
+  nil
+end
+
+case vcs
+when VCS::SVN
   cmd = "svn diff --diff-cmd=diff -x-pU0"
   change = diff2index(cmd, ARGV)
-elsif File.directory?(".git")
+when VCS::GIT
   cmd = "git diff -U0"
   change = diff2index(cmd, ARGV) || diff2index(cmd, "--cached", ARGV)
 else
diff --git a/tool/vcs.rb b/tool/vcs.rb
index 4d8936cb54..0f20c6e35a 100644
--- a/tool/vcs.rb
+++ b/tool/vcs.rb
@@ -73,15 +73,11 @@ class VCS
 
   def self.detect(path)
     @@dirs.each do |dir, klass, pred|
-      if pred ? pred[path, dir] : File.directory?(File.join(path, dir))
-        return klass.new(path)
-      end
-      prev = path
+      curr = path
       loop {
-        curr = File.realpath(File.join(prev, '..'))
-        break if curr == prev	# stop at the root directory
-        return klass.new(path) if File.directory?(File.join(curr, dir))
-        prev = curr
+        return klass.new(curr) if pred ? pred[curr, dir] : File.directory?(File.join(curr, dir))
+        prev, curr = curr, File.realpath(File.join(curr, '..'))
+        break if curr == prev # stop at the root directory
       }
     end
     raise VCS::NotFoundError, "does not seem to be under a vcs: #{path}"