[cfe-dev] Source location for the template keyword.

[Enea Zaffanella]

Hello.

It seems that the AST representation is missing information regarding 
the presence and the source location of the 'template' keyword in a few 
expression nodes.

For instance, consider the following example:

template <typename T>
struct S {
   template <class U> static int foo(U*);

   static const unsigned s = sizeof(S<T>::template foo<T>(0));
};

The argument of sizeof is an UnresolvedLookupExpr.
This gets pretty printed as follows:

template <typename T> struct S {
     template <class U> static int foo(U *);
     static const unsigned int s = sizeof (S<T>::foo<T>(0));
};


We were considering the addition of a SourceLocation for the template 
keyword to UnresolvedLookupExpr and similar AST nodes. Such a source 
location will be invalid if the keyword is not written in the sources. 
Afawct, there are examples when such a template keyword is needed (as 
the one above) and other examples where it is just optional; a possibly 
invalid source location should be enough to distinguish among all 
possibilities.

Afawct, the template keyword can appear (it is meant, after the nested 
name specifier and before the declaration name) in the following 
expressions:

   DeclRefExpr
   MemberExpr
   DependentScopeDeclRefExpr
   CXXDependentScopeMemberExpr
   UnresolvedLookupExpr
   UnresolvedMemberExpr

What about CXXUnresolvedConstructExpr?
Are there other cases?

For the DeclRefExpr and MemberExpr nodes, we could add it to the 
ExplicitTemplateArgs structure (even though, strictly speaking, the 
template keyword is not part of the template args ... this way it will 
go after the end of the node, taking no space if there are no explicit 
template arguments).
For the Unresolved* nodes, we guess that it should be stored in the 
common base class OverloadedExpr.

Does this proposal sound OK?

Regards,
Enea.