"url" now has same features as "head"

Specifically, it can accept all the VCS tag specs that head could,
making it more useful for defining stable versions that come from
VCS instead of tarballs.

A new "SoftwareSpecification" class was added to implement this.

This new class holds a "spec" for downloading a software package.
It combines the url (or head url) with the "specs" [1] that head has
been able to take.

This allows both the stable (url) and unstable (head) specification
for a software package to co-exist without stomping on each others
"specs".

[1] "specs" contain instructions on which branch/tag/revision/etc. to use
    from the source repository URL.

Library/Homebrew/formula.rb

@@ -11,6 +11,50 @@ class FormulaUnavailableError <RuntimeError
 end
 
 
+class SoftwareSpecification
+  attr_reader :url, :specs, :using
+
+  VCS_SYMBOLS = {
+    :bzr,     BazaarDownloadStrategy,
+    :curl,    CurlDownloadStrategy,
+    :cvs,     CVSDownloadStrategy,
+    :git,     GitDownloadStrategy,
+    :hg,      MercurialDownloadStrategy,
+    :nounzip, NoUnzipCurlDownloadStrategy,
+    :post,    CurlPostDownloadStrategy,
+    :svn,     SubversionDownloadStrategy,
+  }
+
+  def initialize url, specs=nil
+    raise "No url provided" if url.nil?
+    @url = url
+    unless specs.nil?
+      # Get download strategy hint, if any
+      @using = specs.delete :using
+      # The rest of the specs are for source control
+      @specs = specs
+    end
+  end
+
+  # Returns a suitable DownloadStrategy class that can be
+  # used to retreive this software package.
+  def download_strategy
+    return detect_download_strategy @url if @using.nil?
+
+    # If a class is passed, assume it is a download strategy
+    return @using if @using.kind_of? Class
+
+    detected = VCS_SYMBOLS[@using]
+    raise "Unknown strategy #{@using} was requested." unless detected
+    return detected
+  end
+
+  def detect_version
+    Pathname.new(@url).version
+  end
+end
+
+
 # Derive and define at least @url, see Library/Formula for examples
 class Formula
   include FileUtils
@@ -19,13 +63,24 @@ class Formula
 
   # Homebrew determines the name
   def initialize name='__UNKNOWN__'
+    set_instance_variable 'homepage'
     set_instance_variable 'url'
     set_instance_variable 'head'
     set_instance_variable 'specs'
 
+    set_instance_variable 'stable'
+    set_instance_variable 'unstable'
+
     if @head and (not @url or ARGV.build_head?)
-      @url=@head
+      @url = @head
-      @version='HEAD'
+      @version = 'HEAD'
+      @spec_to_use = @unstable
+    else
+      if @stable.nil?
+        @spec_to_use = SoftwareSpecification.new(@url, @specs)
+      else
+        @spec_to_use = @stable
+      end
     end
 
     raise "No url provided for formula #{name}" if @url.nil?
@@ -33,16 +88,12 @@ class Formula
     validate_variable :name
 
     set_instance_variable 'version'
-    @version ||= Pathname.new(@url).version
+    @version ||= @spec_to_use.detect_version
     validate_variable :version if @version
 
-    set_instance_variable 'homepage'
+    CHECKSUM_TYPES.each { |type| set_instance_variable type }
 
-    CHECKSUM_TYPES.each do |type|
+    @downloader=download_strategy.new @spec_to_use.url, name, version, @spec_to_use.specs
-      set_instance_variable type
-    end
-
-    @downloader=download_strategy.new url, name, version, specs
   end
 
   # if the dir is there, but it's empty we consider it not installed
@@ -52,18 +103,14 @@ class Formula
     return false
   end
 
-  def prefix
-    validate_variable :name
-    validate_variable :version
-    HOMEBREW_CELLAR+@name+@version
-  end
-
   def path
     self.class.path name
   end
 
-  def cached_download
+  def prefix
-    @downloader.cached_location
+    validate_variable :name
+    validate_variable :version
+    HOMEBREW_CELLAR+@name+@version
   end
 
   def bin; prefix+'bin' end
@@ -77,33 +124,19 @@ class Formula
   def include; prefix+'include' end
   def share; prefix+'share' end
 
-  # generally we don't want var stuff inside the keg
-  def var; HOMEBREW_PREFIX+'var' end
   # configuration needs to be preserved past upgrades
   def etc; HOMEBREW_PREFIX+'etc' end
+  # generally we don't want var stuff inside the keg
+  def var; HOMEBREW_PREFIX+'var' end
 
-  # reimplement if we don't autodetect the download strategy you require
+  # Use the @spec_to_use to detect the download strategy.
+  # Can be overriden to force a custom download strategy
   def download_strategy
-    if @specs and @url == @head
+    @spec_to_use.download_strategy
-      vcs = @specs.delete :using
-      if vcs != nil
-        # If a class is passed, assume it is a download strategy
-        return vcs if vcs.kind_of? Class
-
-        case vcs
-        when :bzr then return BazaarDownloadStrategy
-        when :curl then return CurlDownloadStrategy
-        when :cvs then return CVSDownloadStrategy
-        when :git then return GitDownloadStrategy
-        when :hg then return MercurialDownloadStrategy
-        when :svn then return SubversionDownloadStrategy
   end
 
-        raise "Unknown strategy #{vcs} was requested."
+  def cached_download
-      end
+    @downloader.cached_location
-    end
-
-    detect_download_strategy url
   end
 
   # tell the user about any caveats regarding this package, return a string
@@ -213,7 +246,7 @@ class Formula
       require self.path(name)
     end
     begin
-      klass_name =self.class_s(name)
+      klass_name = self.class_s(name)
       klass = eval(klass_name)
     rescue NameError
       # TODO really this text should be encoded into the exception
@@ -284,10 +317,10 @@ protected
   end
 
 private
-  # creates a temporary directory then yields, when the block returns it
+  # Create a temporary directory then yield. When the block returns,
-  # recursively deletes the temporary directory
+  # recursively delete the temporary directory.
   def mktemp
-    # I used /tmp rather than mktemp -td because that generates a directory
+    # I used /tmp rather than `mktemp -td` because that generates a directory
     # name with exotic characters like + in it, and these break badly written
     # scripts that don't escape strings before trying to regexp them :(
 
@@ -336,11 +369,8 @@ EOF
 
   def stage
     HOMEBREW_CACHE.mkpath
-
+    fetched = @downloader.fetch
-    downloaded_tarball = @downloader.fetch
+    verify_download_integrity fetched if fetched.kind_of? Pathname
-    if downloaded_tarball.kind_of? Pathname
-      verify_download_integrity downloaded_tarball
-    end
 
     mktemp do
       @downloader.stage
@@ -427,6 +457,8 @@ EOF
   end
 
   class << self
+    # The methods below define the formula DSL.
+    attr_reader :stable, :unstable
 
     def self.attr_rw(*attrs)
       attrs.each do |attr|
@@ -438,13 +470,21 @@ EOF
       end
     end
 
-    attr_rw :url, :version, :homepage, :specs, :deps, :external_deps, *CHECKSUM_TYPES
+    attr_rw :version, :homepage, :specs, :deps, :external_deps
+    attr_rw *CHECKSUM_TYPES
 
     def head val=nil, specs=nil
-      if specs
+      return @head if val.nil?
+      @unstable = SoftwareSpecification.new(val, specs)
+      @head = val
       @specs = specs
     end
-      val.nil? ? @head : @head = val
+
+    def url val=nil, specs=nil
+      return @url if val.nil?
+      @stable = SoftwareSpecification.new(val, specs)
+      @url = val
+      @specs = specs
     end
 
     def depends_on name