Always find git and svn without trying hard

Two wrapper scripts that find git and svn using the ENV variables we support and then searching through the PATH and looking inside Xcode.app if necessary.

Now just calling git or svn in Homebrew code will find and exec the right tool and we can stop fussing.

Apologies to @adamv who is probably unimpressed that the cmds directory has non-commands in it now. If it's consolation these are temporary pending some more work on superenv whereby some more directories are created under the superenv root.

Library/Contributions/cmds/git

@@ -0,0 +1,51 @@
+#!/usr/bin/ruby -W0
+# This script because we support $GIT, $HOMEBREW_SVN, etc. and Xcode-only
+# configurations. Order is careful to be what the user would want.
+
+F = File.basename(__FILE__).freeze
+D = File.expand_path(File.dirname(__FILE__)).freeze
+
+def exec *args
+  # prevent fork-bombs
+  arg0 = if args.size == 1
+    args.first.split(' ')
+  else
+    args
+  end.first
+  return if arg0 =~ /^#{F}/i
+  return if File.expand_path(arg0) == File.expand_path(__FILE__)
+
+  if args[1] == '-print-path' and File.executable? args[0]
+    puts args[0]
+    exit 0
+  else
+    Kernel.exec *args
+  end
+end
+
+case F.downcase
+  when 'git' then %W{HOMEBREW_GIT GIT}
+  when 'svn' then "HOMEBREW_SVN"
+  else []
+end.each do |key|
+  exec ENV[key], *ARGV if ENV[key] and File.executable? ENV[key]
+end
+
+brew_version = File.expand_path("#{D}/../../../bin/#{F}")
+exec brew_version, *ARGV if File.executable? brew_version
+
+`/usr/bin/which -a #{F} 2>/dev/null`.split("\n").each do |path|
+  exec path, *ARGV
+end
+
+# xcrun hangs if xcode-select is set to "/"
+path = `/usr/bin/xcode-select -print-path 2>/dev/null`.chomp
+if path != "/"
+  path = `/usr/bin/xcrun -find #{F} 2>/dev/null`.chomp
+  exec path, *ARGV if File.executable? path
+end
+
+path = "/Applications/Xcode.app/Contents/Developer/usr/bin/#{F}"
+exec path, *ARGV if File.executable? path
+
+abort "You must: brew install #{F}"

Library/Contributions/cmds/svn

@@ -0,0 +1 @@
+git

Library/Homebrew/cmd/--env.rb

@@ -23,7 +23,7 @@ module Homebrew extend self
       CMAKE_PREFIX_PATH CMAKE_INCLUDE_PATH CMAKE_FRAMEWORK_PATH MAKEFLAGS
       MACOSX_DEPLOYMENT_TARGET PKG_CONFIG_PATH HOMEBREW_BUILD_FROM_SOURCE
       HOMEBREW_DEBUG HOMEBREW_MAKE_JOBS HOMEBREW_VERBOSE HOMEBREW_USE_CLANG
-      HOMEBREW_USE_GCC HOMEBREW_USE_LLVM HOMEBREW_SVN
+      HOMEBREW_USE_GCC HOMEBREW_USE_LLVM HOMEBREW_SVN HOMEBREW_GIT
       MAKE GIT CPP
       ACLOCAL_PATH OBJC PATH ].select{ |key| env[key] }
   end

Library/Homebrew/download_strategy.rb

@@ -210,7 +210,7 @@ end
 class SubversionDownloadStrategy < AbstractDownloadStrategy
   def initialize name, package
     super
-    @@svn ||= find_svn
+    @@svn ||= 'svn'
     @unique_token="#{name}--svn" unless name.to_s.empty? or name == '__UNKNOWN__'
     @unique_token += "-HEAD" if ARGV.include? '--HEAD'
     @co=HOMEBREW_CACHE+@unique_token
@@ -269,20 +269,12 @@ class SubversionDownloadStrategy < AbstractDownloadStrategy
     args << '--ignore-externals' if ignore_externals
     quiet_safe_system(*args)
   end
-
-  # Try HOMEBREW_SVN, a Homebrew-built svn, and finally the OS X system svn.
-  # Not all features are available in the 10.5 system-provided svn.
-  def find_svn
-    return ENV['HOMEBREW_SVN'] if ENV['HOMEBREW_SVN']
-    return "#{HOMEBREW_PREFIX}/bin/svn" if File.exist? "#{HOMEBREW_PREFIX}/bin/svn"
-    return MacOS.locate 'svn'
-  end
 end
 
 # Require a newer version of Subversion than 1.4.x (Leopard-provided version)
 class StrictSubversionDownloadStrategy < SubversionDownloadStrategy
   def find_svn
-    exe = super
+    exe = `svn -print-path`
     `#{exe} --version` =~ /version (\d+\.\d+(\.\d+)*)/
     svn_version = $1
     version_tuple=svn_version.split(".").collect {|v|Integer(v)}
@@ -316,7 +308,7 @@ end
 class GitDownloadStrategy < AbstractDownloadStrategy
   def initialize name, package
     super
-    @@git ||= find_git
+    @@git ||= 'git'
     @unique_token="#{name}--git" unless name.to_s.empty? or name == '__UNKNOWN__'
     @clone=HOMEBREW_CACHE+@unique_token
   end
@@ -334,7 +326,7 @@ class GitDownloadStrategy < AbstractDownloadStrategy
   end
 
   def fetch
-    raise "You must install Git: brew install git" unless which "git"
+    raise "You must: brew install git" unless which "git"
 
     ohai "Cloning #{@url}"
 
@@ -405,13 +397,6 @@ class GitDownloadStrategy < AbstractDownloadStrategy
       end
     end
   end
-
-  # Try GIT, a Homebrew-built Git, and finally the OS X system Git.
-  def find_git
-    return ENV['GIT'] if ENV['GIT']
-    return "#{HOMEBREW_PREFIX}/bin/git" if File.exist? "#{HOMEBREW_PREFIX}/bin/git"
-    return MacOS.locate 'git'
-  end
 end
 
 class CVSDownloadStrategy < AbstractDownloadStrategy