Not GUI based, but completely syntax driven: my company's Smart Differencer tools for many langauges (incluiding Java, C#, C++, PHP, Python, JavaScript, HTML, XML, COBOL,...)
The Smart Differencer parses the source text like the compiler, so it understands that language syntax and structures the way the compiler does. It compares these structures (using ASTs) to determine the "least edit distance" in terms of edit actions (move, copy, delete, replace, rename-identifier-in-block) on these structures and report them.
In your example, it would know the curly brace on the right belongs to foo, not bar, and would tell you that the entire statement involving bar was simply deleted.
The output style is diff-like if you want to feed the result to another tool, or more human readable if you want to examine it directly.