rsmith added a comment.
The right way to handle this is to pass both the ultimately-selected
declaration and the declaration found by name lookup into the calls to
`MarkAnyDeclReferenced` and friends. We should mark the selected declaration as
`Used` (when appropriate), and mark the found declaration as `Referenced`.
We should not be trying to reconstruct which using declarations are in scope
after the fact. Only declarations actually found by name lookup and then
selected by the context performing the lookup should be marked referenced.
(There may be cases where name lookup discards equivalent lookup results that
are not redeclarations of one another, though, and to handle such cases
properly, you may need to teach name lookup to track a list of found
declarations rather than only one.)
================
Comment at: lib/Sema/Sema.cpp:1884-1885
+ ND = NA->getAliasedNamespace();
+ if (auto *NNS = NA->getQualifier())
+ MarkNamespaceAliasReferenced(NNS->getAsNamespaceAlias());
+ }
----------------
The loop and recursion here -- and indeed this whole function -- seem
unnecessary.
```
namespace A {} // #1
namespace X {
namespace B = A; // #2
}
namespace Y = X; // #3
namespace C = Y::B; // #4
```
Declaration `#4` should mark `#2` and `#3` referenced. So the only
'unreferenced namespace alias' warning we should get here is for `#4` -- and
there is no need for marking `#4` as referenced to affect `#2` or `#3`.
================
Comment at: lib/Sema/Sema.cpp:1890-1891
+
+/// \brief Mark as referenced any 'using declaration' that have introduced
+/// the given declaration in the current context.
+void Sema::MarkUsingReferenced(Decl *D, CXXScopeSpec *SS, Expr *E) {
----------------
Why is this ever appropriate? I would think we should just mark the named
declaration from the relevant lookup as referenced in all cases.
https://reviews.llvm.org/D46190
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