[cfe-commits] [Patch][Review request] RecursiveASTVisitor can now traverse template specializations

[Benoit Belley]

Hi John,

I have made good progress today with the help of your comments.  I’ll test some more before submitting the new patch.

Le 2010-08-30 à 21:08, John McCall a écrit :

On Aug 30, 2010, at 5:33 PM, Benoit Belley wrote:
I think that I’ll need a bit more explanation here. The infinite recursion occurs while traversing the instantiations of the class template definition and I do want to traverse these instantiations. That’s the whole point of my proposed change.

Yes, I understood that.  My point is that you're visiting the instantiations regardless of whether the current template declaration you're visiting is a redeclaration or not.  This creates two problems:  first, you end up visiting the instantiations multiple times if the template is redeclared; and second, if the template is redeclared within itself (which can only be done with friend declarations), you end up visiting it recursively, which blows up the stack.  The solution is to only visit implicit instantiations when you visit a pattern definition.

 template <class T> class A;  // <- don't visit any instantiations here
 class B { template <class T> friend class A; };  // <- or here
 template <class T> class A { ... }; // <- okay to visit implicit instantiations here

By the way, here’s one more bit of information.  The problem does not occur when the template is explicitly instantiated:

Yes, because your implementation of TraverseImplicitClassInstantiations ignores explicit instantiations.  So when you visit the explicit instantiation, you visit its friend decl, whereupon you visit all the implicit instantiations, which (as long as there are none) doesn't cause an infinite recursion because you ignore the explicit instantiation.


Visiting the class template definition while skipping the re-declarations turns out to be not so obvious. FunctionDecl and VarDecl have isThisDeclarationADefiniton(). RecordDecl has getDefintion()... But, ClassTemplateDecl has none of this. I have found that the following trick seems to work in practice:

    ClassTemplateDecl* D = ...;
    CXXRecordDecl* TemplDecl = D->getTemplatedDecl();
    if (TemplDecl) {
      if (CXXRecordDecl* TemplDef = TemplDecl->getDefinition()) {
        if (TemplDecl == TemplDef) {
          TRY_TO(TraverseImplicitClassInstantiations(D));
        }
      }
    }

 Is this the correct approach ?



Also, can you explain why you're not visiting the written type of explicit specializations when your flag is set?  That doesn't seem very general.


Miscomprehension of the Clang AST from my side...


John.
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Thanks for being patient. I am new to the Clang AST, so I am learning as I go.
Benoit


Benoit Belley
Sr Principal Developer
M&E-Product Development Group

Autodesk Canada Inc.
10 Rue Duke
Montreal, Quebec  H3C 2L7
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Direct 514 954-7154



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