[cfe-dev] libclang and MemberRefExpr

[Erik Verbruggen]

On 13 May 2011, at 17:56, Douglas Gregor wrote:

> 
> On May 13, 2011, at 5:13 AM, Erik Verbruggen wrote:
> 
>> On 12 May, 2011,at 05:43 PM, Douglas Gregor <dgregor at apple.com> wrote:
>> 
>>> However, if the name isn't a simple identifier ("x.operator[]"), then you can still get the location of the start of the member name ("operator"), but when you ask for the range, you'll only get the range of that one token.
>>> 
>>> Back when we designed libclang, Clang didn't even have the information about where the three tokens of "operator[]" were. Now, we actually have this information via DeclarationNameInfo, so it would make sense to add an API for specifically what you want. Here is a general API that (I think!) could fully solve this problem:
>>> 
>>> CXSourceRange clang_getCursorReferenceNameRange(CXCursor C, unsigned NameFlags, unsigned PieceIndex);
>>> 
>>> where C is a cursor that references something else (e.g., a member reference, declaration reference, type reference, etc.), and returns the source range covering the reference itself. The two "unsigned" values would be for configurability:
>>> 
>>> - NameFlags could be bitset with three independent flags: WantQualifier (to ask it to include the nested-name-specifier, e.g., Foo:: in x.Foo::y, in the range), WantTemplateArgs (to ask it to include the explicit template arguments, e.g., <int> in x.f<int>, in the range), and WantSinglePiece (described below).
>>> 
>>> - WantPiece/PieceIndex is my attempt at handling cases where the name itself isn't contiguous. For example, imagine the expression "a[y]", which ends up referring to an overloaded operator[]. The source range for the full operator name is, effectively, "[y]", since the name has been split into two parts. However, that's not necessarily useful, so WantPiece would indicate that we want a range covering only one piece of the name, where PieceIndex==0 indicates that we want the '[' and PieceIndex==1 indicates that we want the ']'.
>> 
>> So for "operator[]" you would 3 pieces? Or just 1?
> 
> Probably just one.

After a bit of thought and some explorative programming, I'm not sure if this API would be covering all cases. It would work for C/ObjC, but C++ is (as usual) a bit more tricky, especially with conversion operators. For example:

struct Something {
  operator const std::string &();
};

void foo() {
  Something s;
  s.operator const  std::string &(); // <-- this line
}

In the call to the conversion operator, the visitor will only give a MemberRefExpr as node, and no more detail on the right-hand side of the expression. But what is in there, is a TypeRef. Actually, it can by any id-expression, so it might even be something like "some_template<some_type, 1 + 2 + 3>". (And I do not know if c++0x is going to add some more cases...) So I am wondering if this function might be too limited to be really useful, or if it would still make sense for the other cases.

-- Erik.

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