[cfe-dev] Patch for C++ namespaces

[Argiris Kirtzidis]

Chris Lattner wrote:
>> For:
>> namespace A { int x; }
>> namespace A { int y; }
>>
>> There are two NamespaceDecls created and reported at 
>> ASTConsumer::HandleTopLevelDecl, but 'A' refers only to the first one 
>> (the 'original' namespace).
>> And while there's no list of decls associated with NamespaceDecls 
>> yet, the intention is that the 'original namespace' will contain the 
>> list (y will be associated with the first NamespaceDecl).
>
> Ok.
>
>> By reporting 2 namespace decls, the AST maps to the source code 
>> better, and a refactoring tool would be able to do (for example) 
>> "rename all 'A' namespaces" by traversing the AST.
>>
>> If this sound reasonable, how about adding a OriginalNamespace member 
>> to NamespaceDecl so that extended namespace definition decls point to 
>> the 'original' one?
>
> I think we should tackle this in a more systematic way.  All "merging" 
> of decls should be treated the same.  It really would be nice to be 
> able to walk all declarations of some decl.

A unified way to walk all 'merged' declaration would be great. How about 
I commit namespaces as it is (minus NamespaceScope), so that a way to 
deal generally with merged decls would
consider NamespaceDecls too.
>
> The best way to implement this (in terms of space efficiency) is an 
> on-the-side DenseMap<Decl*,Decl*> which would implement a linked list 
> of decls.  Then each decl can just have one bit that says whether it 
> has an entry in the map (i.e. whether there is a 'next').  This can be 
> hidden around behind an accessor, just like the attribute stuff is.  
> Does this seem reasonable?

That's a good idea!


-Argiris