Added new command "versions"

Library/Contributions/brew_bash_completion.sh

@@ -11,7 +11,7 @@ _brew_to_completion()
     [[ ${COMP_CWORD} -eq 1 ]] && {
         local actions="--cache --cellar --config --env --prefix --repository audit cat cleanup
             configure create deps doctor edit fetch help home info install link list log options
-            outdated prune remove search test uninstall unlink update uses"
+            outdated prune remove search test uninstall unlink update uses versions"
         local ext=$(\ls $(brew --repository)/Library/Contributions/examples |
                     sed -e "s/\.rb//g" -e "s/brew-//g")
         COMPREPLY=( $(compgen -W "${actions} ${ext}" -- ${cur}) )
@@ -28,7 +28,7 @@ _brew_to_completion()
 
     case "$prev" in
     # Commands that take a formula
-    cat|deps|edit|fetch|home|homepage|info|install|log|missing|options|uses)
+    cat|deps|edit|fetch|home|homepage|info|install|log|missing|options|uses|versions)
         # handle standard --options
         if [[ "$prev" == "install" && "$cur" == --* ]]; then
             local opts=$(

Library/Homebrew/cmd/versions.rb

@@ -0,0 +1,91 @@
+require 'formula'
+
+module Homebrew extend self
+
+  module Versions
+
+    # The commit SHA for a specific version of a formula
+    def self.sha_for name, version
+      shas_for(name).each do |sha|
+        return sha if version == version_for(name, sha)
+      end
+
+      nil
+    end
+
+    # All SHAs of the commits the named formula has been changed in
+    def self.shas_for name
+      `git --git-dir=#{HOMEBREW_REPOSITORY}/.git rev-list HEAD^ -- Library/Formula/#{name}.rb`.split
+    end
+
+    # Returns the version number for the named formula and the given commit SHA
+    def self.version_for name, sha
+      code = `git --git-dir=#{HOMEBREW_REPOSITORY}/.git show #{sha}:Library/Formula/#{name}.rb`
+      version = code.match(/class #{Formula.class_s name} < ?Formula.*?(?:version\s|@version\s*=)\s*(?:'|")(.+?)(?:'|").*?end\s/m)
+      if version.nil?
+        url = code.match(/class #{Formula.class_s name} < ?Formula.*?(?:url\s|@url\s*=)\s*(?:'|")(.+?)(?:'|").*?end\s/m)
+        if url.nil?
+          head = code.match(/class #{Formula.class_s name} < ?Formula.*?head\s'(.*?)'.*?end\s\s/m)
+          if head.nil?
+            opoo "Version of #{name} could not be determined for #{sha}."
+            nil
+          else
+            'HEAD'
+          end
+        else
+          Pathname.new(url[1]).version
+        end
+      else
+        version[1]
+      end
+    end
+
+    # All older versions of a formula together with the SHA of their most recent
+    # revision
+    def self.old_versions(formula)
+      old_versions = []
+
+      shas_for(formula.name).each do |sha|
+        old_version = version_for formula.name, sha
+
+        if old_version != formula.version &&
+           (old_versions.empty? || old_version != old_versions.last[0])
+          old_versions << [old_version, sha]
+        end
+      end
+
+      old_versions
+    end
+
+  end
+
+  def versions
+    puts "Listing older versions for: #{ARGV.formulae.join(', ')}"
+
+    puts <<-EOS.undent
+
+      If you want to install one of these old versions run `git reset --hard
+      $COMMIT_ID_OF_VERSION` in "#{HOMEBREW_REPOSITORY}". After that you can install the formula
+      like usual with `brew install formula`. When you're done use `git reset --hard
+      master@{1}` in "#{HOMEBREW_REPOSITORY}" to get back to the most recent versions again.
+
+      WARNING: This also reverts Homebrew itself to an old revision. This may lead to
+      broken installations and/or not being able to install an old formula at all.
+    EOS
+
+    ARGV.formulae.all? do |f|
+      old_versions = Versions.old_versions f
+
+      if old_versions.empty?
+        puts "\nThere are no older versions for \"#{f.name}\" (current: #{f.version})."
+      else
+        puts "\nOlder versions for \"#{f.name}\" (current: #{f.version}):\n"
+
+        max_size = 0
+        old_versions.each { |v| max_size = v[0].size if v[0].size > max_size }
+        old_versions.each { |v| puts '  %s (%s)' % [v[0].ljust(max_size), v[1]] }
+      end
+    end
+  end
+
+end