Make luarocks "just work" with lua

Fixes Homebrew/homebrew#5735.

Our default install now doesn't make `/usr/local` group writable in an attempt to "play nicely", this caused luarocks to refuse to install anything because it would assume a non-writable prefix would mean it couldn't write any files. Which is an incorrect check since it only installs files to `prefix/lib`. So the check is removed with a patch if Homebrew is installed to `/usr/local`.

Formula/lua.rb

@@ -31,6 +31,10 @@ class Lua < Formula
       s.gsub! "INSTALL_MAN= ${prefix}/man/man1", "INSTALL_MAN= ${prefix}/share/man/man1"
     end
 
+    # this ensures that this symlinking for lua starts at lib/lua/5.1 and not
+    # below that, thus making luarocks work
+    (HOMEBREW_PREFIX/"lib/lua"/version.split('.')[0..1].join('.')).mkpath
+
     system "make", "macosx", "INSTALL_TOP=#{prefix}", "INSTALL_MAN=#{man1}"
     system "make", "install", "INSTALL_TOP=#{prefix}", "INSTALL_MAN=#{man1}"
 

Formula/luarocks.rb

@@ -11,6 +11,10 @@ class Luarocks < Formula
 
   fails_with_llvm "Lua itself compiles with llvm, but may fail when other software trys to link."
 
+  def patches
+    DATA if HOMEBREW_PREFIX.to_s == '/usr/local'
+  end
+
   def options
     [['--with-luajit', 'Use LuaJIT instead of the stock Lua.']]
   end
@@ -18,7 +22,7 @@ class Luarocks < Formula
   def install
     # Install to the Cellar, but direct modules to HOMEBREW_PREFIX
     args = ["--prefix=#{prefix}",
-            "--rocks-tree=#{HOMEBREW_PREFIX}/lib/luarocks",
+            "--rocks-tree=#{HOMEBREW_PREFIX}",
             "--sysconfdir=#{etc}/luarocks"]
 
     if use_luajit?
@@ -31,9 +35,39 @@ class Luarocks < Formula
     system "make install"
   end
 
+  def caveats; <<-EOS.undent
+    Luarocks now "just works" but this means any rocks you installed previously
+    will need to be moved from `lib/luarocks/lib/luarocks` to `lib/luarocks`.
+    You'll probably have a better time of it all if you just reinstall them.
+    EOS
+  end
+
   def test
     opoo "Luarocks test script installs 'lpeg'"
     system "luarocks install lpeg"
-    system "lua", "-lluarocks.loader", "-llpeg", "-e", 'print ("Hello World!")'
+    system "lua", "-llpeg", "-e", 'print ("Hello World!")'
   end
 end
+
+
+# this patch because we set the permissions of /usr/local to root owned
+# not user writable to be "good" citizens of /usr/local. Actually LUA is being
+# pedantic since all the directories it wants under /usr/local are writable
+# so we just return true. Naughty, but I don't know LUA and don't want to
+# write a better patch.
+__END__
+diff --git a/src/luarocks/fs/lua.lua b/src/luarocks/fs/lua.lua
+index 3a547fe..ca4ddc5 100644
+--- a/src/luarocks/fs/lua.lua
++++ b/src/luarocks/fs/lua.lua
+@@ -619,10 +619,5 @@ end
+ -- @return boolean or (boolean, string): true on success, false on failure,
+ -- plus an error message.
+ function check_command_permissions(flags)
+-   local root_dir = path.root_dir(cfg.rocks_dir)
+-   if not flags["local"] and not fs.is_writable(root_dir) then
+-      return nil, "Your user does not have write permissions in " .. root_dir ..
+-                  " \n-- you may want to run as a privileged user or use your local tree with --local."
+-   end
+    return true
+ end