Added a new AST transformation pass called the

"Playground Transform."  This is an
instrumentation pass that adds calls to a
function called playground_log at locations of
interest.  Roughly speaking, these locations are

- Initialization of variables
- Modification of variables
- Expressions returning values
- Application of mutating methods on objects

The playground transform currently only finds
modifications of variables, but the intent is to
make all of these cases work.

It is enabled by a frontend option, and can
also be invoked by calling

swift::performPlaygroundTransform(SF)

which is the way LLDB, its main client, will
use it.

The frontend option is intended for testing,
and indeed I will add tests for this
transformation in the coming week as I bring
more functionality online.


Swift SVN r14801

lib/Frontend/CompilerInvocation.cpp

@@ -96,6 +96,10 @@ static bool ParseFrontendArgs(FrontendOptions &Opts, ArgList &Args,
     Opts.PrintStats = true;
   }
 
+  if (Args.hasArg(OPT_playground)) {
+    Opts.Playground = true;
+  }
+
   if (const Arg *A = Args.getLastArg(OPT_help, OPT_help_hidden)) {
     if (A->getOption().matches(OPT_help)) {
       Opts.PrintHelp = true;