Encode formula revision in installation prefix

In order to allow kegs built with the same version but differing formula
revisions to coexist, we must encode the revision as part of the keg's
name. This is necessary to actually perform an upgrade, as we cannot
upgrade a keg in-place, and temporarily moving it pending the result of
the upgrade is error-prone and potentially slow.

To accomplish this, we introduce a new Formula#pkg_version method that
concatenates the active_spec version with the formula revision. An
exception is made for a formula that has no revision: the tag is
omitted. This preserves compatibility with existing installations.

1 files changed, 4 insertions, 2 deletions

diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 6ad5eae3a..07fcc5a67 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -10,6 +10,7 @@ require 'build_options'
 require 'formulary'
 require 'software_spec'
 require 'install_renamed'
+require 'pkg_version'
 
 class Formula
   include FileUtils
@@ -18,7 +19,7 @@ class Formula
 
   attr_reader :name, :path, :homepage, :build
   attr_reader :stable, :bottle, :devel, :head, :active_spec
-  attr_reader :revision
+  attr_reader :pkg_version, :revision
 
   # The current working directory during builds and tests.
   # Will only be non-nil inside #stage and #test.
@@ -55,6 +56,7 @@ class Formula
     @active_spec = determine_active_spec
     validate_attributes :url, :name, :version
     @build = determine_build_options
+    @pkg_version = PkgVersion.new(version, revision)
 
     @pin = FormulaPin.new(self)
 
@@ -152,7 +154,7 @@ class Formula
     Keg.new(installed_prefix).version
   end
 
-  def prefix(v=version)
+  def prefix(v=pkg_version)
     Pathname.new("#{HOMEBREW_CELLAR}/#{name}/#{v}")
   end
   def rack; prefix.parent end