Context-aware merge?

Is there any diff/merge tool for programming languages, that works in a syntax-aware way (like XML Diff Tool), doing more than compare line-by-line (and optionally ignoring whitespace).

I'm interested in a program actually following the language syntax and delimeters, suggesting changes without breaking syntactic correctness, or bundling statements separated over multiple lines. Example behavior would be:

*upon finding an if(){ which introduces an extra nesting level automatically bundle the closing brace } several lines below with it.)

*keep matching syntax elements together, avoid silliness like removing a block tends to create:

 int function_A()
 { 
     int ret;
     ret = something;
     ret += something_else;

      return ret;
  }

  int function_B()
  { 
     if(valid)
     {
         int ret;
         ret = something;
         ret += something_else;

          return ret;
      }

       else return -1;
  }

Personally, I'd love to find software capable of handling C++ syntax, but knowing about solutions for other languages would be interesting too.

Beyond Compare does some of what you're asking. It doesn't maintain syntactical correctness or compare language blocks at a time, but it can do the following:

• Some understanding of language syntax, so it can do syntax highlighting of compared files, and it can also recognize and optionally ignore unimportant differences (like comments, including multiline comments).
• Support for using external conversion programs for loading and saving data. Out of the box, it supports using this to prettify XML and HTML before comparing it. You could set up GNU Indent to standardize syntax before comparing two C files.
• Optional line weights to let you give a higher weight to matching, e.g., closing braces. I've not tried this feature.
• Replacements, to ignore for a single session every place where old_variable_name on the left was replaced with new_variable_name on the right.

It's by far the best diff-and-merge tool that I've used. It's also cross platform, cheap ($30 for standard, $50 for pro), and has a very generous evaluation period, so it's worth a try.