[cfe-dev] annotation token documentation

[Douglas Gregor]

Hi Argiris,

On Jan 6, 2009, at 10:47 PM, Argiris Kirtzidis wrote:

> Hi Chris & Doug,
>
> Chris Lattner wrote:
>> After my little fun hacking on annotation tokens, I decided to  
>> write up some documentation so that I'd remember how they work the  
>> next time around:
>> http://clang.llvm.org/docs/InternalsManual.html#AnnotationToken
>
> Thanks a lot for documenting it!
>
>>
>> Second, I think it would be interesting to consider handling the  
>> "negative" case (when an identifier is not a type) by turning the  
>> identifier into an annotation token as well, representing the  
>> variable it resolves to (which could be null if it refers to  
>> nothing).  Right now, if we see an identifier in the token stream,  
>> we don't know if that means it is unresolved or whether it means  
>> that it is a variable and backtracking already analyzed but did not  
>> change it.
>>
>> Argiris, do you think it would make sense to make a new  
>> annot_variable that contains a (potentially null) pointer to a  
>> variable decl?  Even without backtracking, this would reduce name  
>> lookups in C: right now we try to decide if something is a type  
>> (which requires a lookup) then decide its not, so we handle it as a  
>> variable (requiring another lookup).  Specifically, things like:
>>
>> int x = sizeof(x);
>>
>> first call Sema::isTypeName then call Sema::LookupDecl.  If the  
>> parser just called a "lookup the decl for this identifier" method,  
>> it could annotate it once and avoid the second lookup.
>
> This would work really well in combination with the suggestion by  
> Doug about unifying the "identifier inquiring" methods in the  
> Actions API. Something like "LookupIdentifier" which returns an enum  
> describing it and optionally returning a void* through an out  
> parameter ?

Yep, that's what I had in mind. The name could be (at least) a type,  
an object/function, a type template, a function template, the current  
class name (which is also a type), or the current class template name  
(which is also both a type and a type template).

>
>
> Douglas Gregor wrote:
>> On Jan 5, 2009, at 10:13 PM, Chris Lattner wrote:
>>
>>  One thing we have to be careful of is that a given identifier can  
>> be  looked up in different ways in different contexts, so we have  
>> to know  when to throw away the results of a previous lookup. For  
>> example, and  identifier 'x' prior to a '::' is looked up  
>> differently that 'x' if it  is followed by something else.
>>
>>
>
> AFAIK an identifier followed by a '::' would always be looked up in  
> a different context (using ActOnCXXNestedNameSpecifier) so there  
> wouldn't be a need to change a previous annotation.

Okay.

	- Doug