[PATCH] D47623: [clangd] Avoid indexing decls associated with friend decls.

[Eric Liu via Phabricator via cfe-commits]

ioeric added inline comments.


================
Comment at: clangd/index/SymbolCollector.cpp:293
   assert(CompletionAllocator && CompletionTUInfo);
+  // A declaration created for a friend declaration should not be used as the
+  // canonical declaration in the index.
----------------
ilya-biryukov wrote:
> Maybe move this closer to `shouldFilterDecl()`? We have similar filters there.
> That would also mean we properly add the reference counts for friend declarations that get a normal declaration after their usage later.
I didn't put this filter there because I think it's a bit more special than those filters in `shouldFilterDecl`. We check the `OrigD` and we could potentially replace `D` with `OrigD`. We could change `shouldFilterDecl` to handle that, but I'm not sure if it's worth it.

Reference counting for friend declarations is actually a bit tricky as USRs of the generated declarations might be ambiguous.

 Consider the following exmaple:
```
namespace a {                
class A {};                  
namespace b { class B { friend class A; };  }  // b                          
} // a                            
```

I would expect the generated friend decl to be `a::A`, but it's actually `a::b::A`! So getting USR right is a bit tricky, and I think it's probably ok to ignore references in friend decls.

For reference, `[namespace.memdef]p3`:
"If the name in a friend declaration is neither qualified nor a template-id and the declaration is a function or an elaborated-type-specifier, the lookup to determine whether the entity has been previously declared shall not consider any scopes outside the innermost enclosing namespace.


Repository:
  rCTE Clang Tools Extra

https://reviews.llvm.org/D47623