1 files changed, 52 insertions, 0 deletions
diff --git a/tool/ruby-version.rb b/tool/ruby-version.rb
new file mode 100755
index 0000000000..3bbec576e1
--- /dev/null
+++ b/tool/ruby-version.rb
@@ -0,0 +1,52 @@
+#!/usr/bin/env ruby
+
+module RubyVersion
+  def self.tag(version)
+    major_version = Integer(version.split('.', 2)[0])
+    if major_version >= 4
+      "v#{version}"
+    else
+      "v#{version.tr('.-', '_')}"
+    end
+  end
+
+  # Return the previous version to be used for release diff links.
+  # For a ".0" version, it returns the previous ".0" version.
+  # For a non-".0" version, it returns the previous teeny version.
+  def self.previous(version)
+    unless /\A(\d+)\.(\d+)\.(\d+)(?:-(?:preview|rc)\d+)?\z/ =~ version
+      raise "unexpected version string '#{version}'"
+    end
+    major = Integer($1)
+    minor = Integer($2)
+    teeny = Integer($3)
+
+    if teeny != 0
+      "#{major}.#{minor}.#{teeny-1}"
+    elsif minor != 0 # && teeny == 0
+      "#{major}.#{minor-1}.#{teeny}"
+    else # minor == 0 && teeny == 0
+      case major
+      when 3
+        "2.7.0"
+      when 4
+        "3.4.0"
+      else
+        raise "it doesn't know what is the previous version of '#{version}'"
+      end
+    end
+  end
+end
+
+if __FILE__ == $0
+  case ARGV[0]
+  when "tag"
+    print RubyVersion.tag(ARGV[1])
+  when "previous"
+    print RubyVersion.previous(ARGV[1])
+  when "previous-tag"
+    print RubyVersion.tag(RubyVersion.previous(ARGV[1]))
+  else
+    "#{$0}: unexpected command #{ARGV[0].inspect}"
+  end
+end