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RE: [cdt-dev] Using the CDT parser for debug expressions?

Title: Using the CDT parser for debug expressions?
Hi Ken,
I'm of course not an expert but I've been down this path before.  There's some more API for this since the last time I looked, but in 5.0.x I thought this would be a way to do this:
IStorage storage = /* some custom in-memory implementation */;
IASTTranslationUnit tu = CDOM.getTranslationUnit(storage, project);

But I see that 'storage' is only used to fetch a path, and then the core assumes everything's in a file.  I assume the debugger won't want to write a lot of files to populate the Variables view...

Another approach requires touching non-API code but you should at least be able to control where the parsed content comes from:

ILanguage language = GCCLanguage.DEFAULT_INSTANCE;
IIndex index = CCorePlugin.getIndexManager.getIndex(project, 0 /* ?? */);

IScanner scanner = new CPreprocessor/**non API**/(.. lots of stuff you have to implement or instantiate...);
ISourceCodeParser parser = language.createParser(scanner, ParserMode.QUICK_PARSE /* ?? */, new DefaultLogService(), index);

IASTTranslationUnit tu = parser.parse();

... then see what 'tu' has to offer.  N.B. you'll probably need to wrap the _expression_ in a dummy function body, like  "void debugger_func()  { /* _expression_ */ } ". 

You would need to manually visit this tree to evaluate the _expression_ or find something that does it for you. 

An important question, though, is how the TU will respond to all the identifiers, struct/class dereferences, etc. it will encounter along the way in a complex _expression_... I think IASTProblem[Holder] nodes will appear in the tree, which you may or may not be able to work around. 

This is where the experts can help more :)

-- Ed

From: Ryall Ken (Nokia-D-MSW/Austin)
Sent: Tuesday, June 09, 2009 1:49 PM
To: cdt-dev@xxxxxxxxxxx
Subject: [cdt-dev] Using the CDT parser for debug expressions?

I have a question for the folks who have more experience with CDT language parsing than I:

The EDC debugger needs to parse and then evaluate C/C++ expressions. The JDT debugger does this for java expressions using an ASTEvaluationEngine. It looks like it can take a snippet of Java code and create a CompilationUnit, which extends ASTNode. The CompilationUnit accepts a visitor (ASTInstructionCompiler) which produces a compiled version of the _expression_ that the debugger can evaluate. This is all done in org.eclipse.jdt.internal.debug.eval.ast.engine and org.eclipse.jdt.internal.debug.eval.ast.instructions

So I'm wondering if I can take the same approach in CDT. It would need to parse a snippet of code but would usually have a translation unit and project context to consider too.

Thanks for your thoughts,

- Ken

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