Fix implementation of [temp.local]p4.

When a template-name is looked up, we need to give injected-class-name
declarations of class templates special treatment, as they denote a
template rather than a type.

Previously we achieved this by applying a filter to the lookup results
after completing name lookup, but that is incorrect in various ways, not
least of which is that it lost all information about access and how
members were named, and the filtering caused us to generally lose
all ambiguity errors between templates and non-templates.

We now preserve the lookup results exactly, and the few places that need
to map from a declaration found by name lookup into a declaration of a
template do so explicitly. Deduplication of repeated lookup results of
the same injected-class-name declaration is done by name lookup instead
of after the fact.

This reinstates r354091, which was previously reverted in r354097
because it exposed bugs in lldb and compiler-rt. Those bugs were fixed
in r354173 and r354174 respectively.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@354176 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 19 insertions, 3 deletions

diff --git a/lib/Sema/SemaLookup.cpp b/lib/Sema/SemaLookup.cpp
index 249be78098..86960e0a1d 100644
--- a/lib/Sema/SemaLookup.cpp
+++ b/lib/Sema/SemaLookup.cpp
@@ -2172,11 +2172,27 @@ bool Sema::LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
         DeclContext::lookup_iterator FirstD = FirstPath->Decls.begin();
         DeclContext::lookup_iterator CurrentD = Path->Decls.begin();
 
+        // Get the decl that we should use for deduplicating this lookup.
+        auto GetRepresentativeDecl = [&](NamedDecl *D) -> Decl * {
+          // C++ [temp.local]p3:
+          //   A lookup that finds an injected-class-name (10.2) can result in
+          //   an ambiguity in certain cases (for example, if it is found in
+          //   more than one base class). If all of the injected-class-names
+          //   that are found refer to specializations of the same class
+          //   template, and if the name is used as a template-name, the
+          //   reference refers to the class template itself and not a
+          //   specialization thereof, and is not ambiguous.
+          if (R.isTemplateNameLookup())
+            if (auto *TD = getAsTemplateNameDecl(D))
+              D = TD;
+          return D->getUnderlyingDecl()->getCanonicalDecl();
+        };
+
         while (FirstD != FirstPath->Decls.end() &&
                CurrentD != Path->Decls.end()) {
-         if ((*FirstD)->getUnderlyingDecl()->getCanonicalDecl() !=
-             (*CurrentD)->getUnderlyingDecl()->getCanonicalDecl())
-           break;
+          if (GetRepresentativeDecl(*FirstD) !=
+              GetRepresentativeDecl(*CurrentD))
+            break;
 
           ++FirstD;
           ++CurrentD;