[cfe-dev] Chaining ASTConsumers

[Vlad]

I've been successful with the following approach:

- use an ASTConsumer implementation that can delegate to yet another instance of an ASTConsumer
- the first consumer performs its ASTConsumer callbacks (and, if necessary, node transformations) *before* the delegate consumer:

ASTConsumer * m_delegate;

void HandleTopLevelDecl (DeclGroupRef group)
{
	for (DeclGroupRef::iterator node = group.begin(), n_limit = group.end (); n != n_lmit; ++ n)
	{
		// [do whatever you want with 'node', including AST transforms: this will typically use DeclVisitor and StmtVisitor to handle just the decls and expressions of interest]
	}

	m_delegate-> HandleTopLevelDecl (visit); // now let the "real" consumer see what we've done
}

// forward other ASTConsumer methods to 'm_delegate' as well so it knowns when a translation unit is done, etc

So, when my ASTConsumer is an AST transformer and m_delegate is, say, a CodeGenerator instance, I get to modify AST just before it gets compiled into native code. It works because the "real" AST consumer (CodeGenerator) only sees the nodes that I want it to see, possibly after a transformation.

Of course, not every AST transform can be done this way, but for additive/substitutive tree transformations this works well and does not require a pretty-printing pass. It is easy to imagine this working for an entire chain/pipeline of AST manipulators.

HTH,
Vlad


On May 7, 2010, at 7:22 AM, Mohamed Yousef wrote:

> Hello ,
> 
> I'm writing a source to source tool, according to list prefred way is Rewriter class , but also i can modify list by a series of traversals
> 
> the problem is Rewriter class method is really primitive,, isn't suitable for big changes (esp. in structure )
> 
> what i'm asking for is, can i chain ASTConsumer's ,,so i can progressively modify AST and pretty-print it finally
> but it looks like (from ParseAST) i would have to Parser -> ASTConsumer ->  pretty-print ->Parser ->ASTConsumer -> .. and so on
> which is very tedious
> 
> is the there an explicit AST data structure ? can i just parse once and modify resulting AST many times  (traverse,add/delete nodes it not re-parse source) ?
> 
> Thanks,
> Mohamed Yousef
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