Can Xtext be used for parsing general purpose programming languages?

I can't speak for what Xtext is or does well.

I can speak to the problem of developing robust tools for processing real languages, based on our experience with the DMS Software Reengineering Toolkit, which we imagine is a language manipulation framework.

First, parsing of real languages usually involves something messy in lexing and/or parsing, due to the historical ways these languages have evolved. Java is pretty clean. C# has context-dependent keywords and a rudimentary preprocessor sort of like C's. C has a full blown preprocessor. C++ is famously "hard to parse" due to ambiguities in the grammar and shenanigans with template syntax. COBOL is fairly ugly, doesn't have any reference grammars, and comes in a variety of dialects. PHP will turn you to stone if you look at it because it is so poorly defined. (DMS has parsers for all of these, used in anger on real applications).

Yet you can parse all of these with most of the available parsing technologies if you try hard enough, usually by abusing the lexer or the parser to achieve your goals (how the GNU guys abused Bison to parse C++ by tangling lexical analysis with symbol table lookup is a nice ugly case in point). But it takes a lot of effort to get the language details right, and the reference manuals are only close approximations of the truth with respect to what the compilers really accept.

If Xtext has a decent parsing engine, one can likely do this with Xtext. A brief perusal of the Xtext site sounds like the lexers and parsers are fairly decent. I didn't see anything about the "Semantic Predicate"s; we have them in DMS and they are lifesavers in some of the really dark corners of parsing. Even using the really good parsing technology (we use GLR parsers), it would be very hard to parse COBOL data declarations (extracting their nesting structure during the parse) without them.

You have an interesting problem in that your language isn't well defined yet. That will make your initial parsers somewhat messy, and you'll revise them a lot. Here's where strong parsing technology helps you: if you can revise your grammar easily you can focus on what you want your language to look like, rather than focusing on fighting the lexer and parser. The fact that you can change your language definition means in fact that if Xtext has some limitations, you can probably bend your language syntax to match without huge amounts of pain. ANTLR does have the proven ability to parse a language pretty much as you imagine it, modulo the usual amount of parser hacking.

What is never discussed is what else is needed to process a language for real. The first thing you need to be able to do is to construct ASTs, which ANTLR and YACC will help you do; I presume Xtext does also. You also need symbol tables, control and data flow analysis (both local and global), and machinery to transform your language into something else (presumably more executable). Doing just symbol tables you will find surprisingly hard; C++ has several hundred pages of "how to look up an identifier"; Java generics are a lot tougher to get right than you might expect. You might also want to prettyprint the AST back to source code, if you want to offer refactorings. (EDIT: Here both ANTLR and Xtext offer what amounts to text-template driven code generation).

Yet these are complex mechanisms that take as much time, if not more than building the parser. The reason DMS exists isn't because it can parse (we view this just as the ante in a poker game), but because all of this other stuff is very hard and we wanted to amortize the cost of doing it all (DMS has, we think, excellent support for all of these mechanisms but YMMV).

On reading the Xtext overview, it sounds like they have some support for symbol tables but it is unclear what kind of assumption is behind it (e.g., for C++ you have to support multiple inheritance and namespaces).

If you are already started down the ANTLR road and have something running, I'd be tempted to stay the course; I doubt if Xtext will offer you a lot of additional help. If you really really want Xtext's editor, then you can probably switch at the price of restructuring what grammar you have (this is a pretty typical price to pay when changing parsing paradigms). Expect most of your work to appear after you get the parser right, in an ad hoc way. I doubt you will find Xtext or ANTLR much different here.

I think nobody implemented Java or C++ because it is a lot of work (even with Xtext) and the existing tools and compilers are excellent. However, you could have a look at Xbase and Xtend, which is the expression language we ship with Xtext. It is built with Xtext and is quite a good proof for what you can build with Xtext. We have done that in about 4 person months.

I did a couple of screencasts on Xtend:

http://blog.efftinge.de/2011/03/xtend-screencast-part-1-basics.html
http://blog.efftinge.de/2011/03/xtend-screencast-part-2-switch.html
http://blog.efftinge.de/2011/03/xtend-screencast-part-3-rich-strings-ie.html

Note, that you can simply embed Xbase expressions into your language.