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:
> ioeric wrote:
> > 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.
> > Reference counting for friend declarations is actually a bit tricky as USRs
> > of the generated declarations might be ambiguous.
> This seems like an obvious bug in the USRs that we should fix. WDYT?
Sorry, I think I was not clear... I think this is intended according to the
standard. So in the example, the qualified name of the friend decl `a::b::A`
is, although confusing, correct, and o the actual problem is not with the USR.
See `[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
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