I was wondering if there is something similar to GCC_XML for C#3; basically a way to represent a program's entire syntactic structure in XML.
Once the representation is created, I was hoping to parse it into an XDocument and interpret or query it from there.
Are there tools out there for this?
The DMS Software Reengineering Toolkit can do this with C# 2/3/4.
DMS has compiler accurate parsers for C# (as well as Java and many other languages).
It automatically builds full Abstract Syntax Trees for whatever it parses. Each AST node is stamped with file/line/column for the token that represents that start of that node, and the final column can be computed by a DMS API call. It attaches comments to tree nodes so they aren't lost. DMS can also regenerate valid code from the AST, or from a modified AST; this enables it to be used for code modification or generation.
It has a built-in option to generate XML from the ASTs, complete with node type, source position (as above), and any associated literal value. The command line call is:
run DMSDomainParser ++XML <path_to_your_file>
DMS itself provides a vast amount of infrastructure for manipulating the ASTs it builds: traversing, pattern matching (against patterns coded essentially in source form), source-to-source transforms.
It has control flow, data flow, points-to analysis, global call graphs for C, COBOL and Java; that's all coming for C#.
DMS was designed to be a better solution than XML for manipulating such code.