[cfe-dev] annotation token documentation

[Douglas Gregor]

On Jan 5, 2009, at 10:13 PM, 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
>
> Argiris, I've come around to being a true believer in the approach, I
> think it is very nifty.  I have a couple of concerns about the current
> implementation though: first it looks like the template-id handling
> code is not really complete.

The completely-broken template-id handling is my fault. There's a  
whole bunch of code that needs to get written, but it's relatively low  
priority (for now).

> 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.


This would be great. Right now, we have isTypeName,  
isCurrentClassName, and isTemplateName, all of which call LookupDecl  
and then return a single yes or no answer. Some code paths call these  
routines multiple times. We'd be better off with a "what does this  
identifier?" action that tells us what we're looking at... and then we  
can store that information in an annotation token.

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.

	- Doug