A install name fix step during install

We currently only fix relative paths, but we should expand this more.

Library/Homebrew/install.rb

@@ -120,6 +120,18 @@ def install f
 
   ohai 'Finishing up' if ARGV.verbose?
 
+  keg = Keg.new f.prefix
+
+  begin
+    keg.fix_install_names
+  rescue Exception => e
+    onoe "Failed to fix install names"
+    puts "The formula built, but you may encounter issues using it or linking other"
+    puts "formula against it."
+    ohai e, e.backtrace if ARGV.debug?
+    show_summary_heading = true
+  end
+
   begin
     require 'cleaner'
     Cleaner.new f
@@ -177,10 +189,10 @@ def install f
 
     # link from Cellar to Prefix
     begin
-      Keg.new(f.prefix).link
+      keg.link
     rescue Exception => e
       onoe "The linking step did not complete successfully"
-      puts "The package built, but is not symlinked into #{HOMEBREW_PREFIX}"
+      puts "The formula built, but is not symlinked into #{HOMEBREW_PREFIX}"
       puts "You can try again using `brew link #{f.name}'"
       if ARGV.debug?
         ohai e, e.backtrace

Library/Homebrew/keg.rb

@@ -122,3 +122,5 @@ protected
     end
   end
 end
+
+require 'keg_fix_install_names'

Library/Homebrew/keg_fix_install_names.rb

@@ -0,0 +1,45 @@
+class Keg
+  def fix_install_names
+    dylibs.each do |dylib|
+      bad_install_names_for dylib do |id, bad_names|
+        dylib.ensure_writable do
+          system "install_name_tool", "-id", id, dylib
+          bad_names.each do |bad_name|
+            # we should be more careful here, check the path we point to exists etc.
+            system "install_name_tool", "-change", bad_name, "@loader_path/#{bad_name}", dylib
+          end
+        end
+      end
+    end
+  end
+
+  private
+
+  OTOOL_RX = /\t(.*) \(compatibility version (\d+\.)*\d+, current version (\d+\.)*\d+\)/
+
+  def bad_install_names_for dylib
+    dylib = dylib.to_s
+
+    ENV['HOMEBREW_DYLIB'] = dylib # solves all shell escaping problems
+    install_names = `otool -L "$HOMEBREW_DYLIB"`.split "\n"
+
+    install_names.shift # first line is fluff
+    install_names.map!{ |s| OTOOL_RX =~ s && $1 }
+    id = install_names.shift
+    install_names.compact!
+    install_names.reject!{ |fn| fn =~ /^@(loader|executable)_path/ }
+    install_names.reject!{ |fn| fn.start_with? '/' }
+
+    unless install_names.empty? and id == dylib # avoid the work if possible
+      yield dylib, install_names
+    end
+  end
+
+  def dylibs
+    if (lib = join 'lib').directory?
+      lib.children.select{ |pn| pn.extname == '.dylib' and not pn.symlink? }
+    else
+      []
+    end
+  end
+end