[modules] Make NamespaceAliasDecl redeclarable, as it should be. This fixes

merging of namespace aliases across modules and improves source fidelity.
Incidentally also fixes PR20816.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217103 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 33 insertions, 30 deletions

diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 5da6546105..858f2c70b0 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -8264,49 +8264,50 @@ Decl *Sema::ActOnAliasDeclaration(Scope *S,
   return NewND;
 }
 
-Decl *Sema::ActOnNamespaceAliasDef(Scope *S,
-                                             SourceLocation NamespaceLoc,
-                                             SourceLocation AliasLoc,
-                                             IdentifierInfo *Alias,
-                                             CXXScopeSpec &SS,
-                                             SourceLocation IdentLoc,
-                                             IdentifierInfo *Ident) {
+Decl *Sema::ActOnNamespaceAliasDef(Scope *S, SourceLocation NamespaceLoc,
+                                   SourceLocation AliasLoc,
+                                   IdentifierInfo *Alias, CXXScopeSpec &SS,
+                                   SourceLocation IdentLoc,
+                                   IdentifierInfo *Ident) {
 
   // Lookup the namespace name.
   LookupResult R(*this, Ident, IdentLoc, LookupNamespaceName);
   LookupParsedName(R, S, &SS);
 
+  if (R.isAmbiguous())
+    return nullptr;
+
+  if (R.empty()) {
+    if (!TryNamespaceTypoCorrection(*this, R, S, SS, IdentLoc, Ident)) {
+      Diag(IdentLoc, diag::err_expected_namespace_name) << SS.getRange();
+      return nullptr;
+    }
+  }
+  assert(!R.isAmbiguous() && !R.empty());
+
   // Check if we have a previous declaration with the same name.
-  NamedDecl *PrevDecl
-    = LookupSingleName(S, Alias, AliasLoc, LookupOrdinaryName, 
-                       ForRedeclaration);
+  NamedDecl *PrevDecl = LookupSingleName(S, Alias, AliasLoc, LookupOrdinaryName,
+                                         ForRedeclaration);
   if (PrevDecl && !isDeclInScope(PrevDecl, CurContext, S))
     PrevDecl = nullptr;
 
   if (PrevDecl) {
     if (NamespaceAliasDecl *AD = dyn_cast<NamespaceAliasDecl>(PrevDecl)) {
       // We already have an alias with the same name that points to the same
-      // namespace, so don't create a new one.
-      // FIXME: At some point, we'll want to create the (redundant)
-      // declaration to maintain better source information.
-      if (!R.isAmbiguous() && !R.empty() &&
-          AD->getNamespace()->Equals(getNamespaceDecl(R.getFoundDecl())))
+      // namespace; check that it matches.
+      if (!AD->getNamespace()->Equals(getNamespaceDecl(R.getFoundDecl()))) {
+        Diag(AliasLoc, diag::err_redefinition_different_namespace_alias)
+          << Alias;
+        Diag(PrevDecl->getLocation(), diag::note_previous_namespace_alias)
+          << AD->getNamespace();
         return nullptr;
-    }
-
-    unsigned DiagID = isa<NamespaceDecl>(PrevDecl) ? diag::err_redefinition :
-      diag::err_redefinition_different_kind;
-    Diag(AliasLoc, DiagID) << Alias;
-    Diag(PrevDecl->getLocation(), diag::note_previous_definition);
-    return nullptr;
-  }
-
-  if (R.isAmbiguous())
-    return nullptr;
-
-  if (R.empty()) {
-    if (!TryNamespaceTypoCorrection(*this, R, S, SS, IdentLoc, Ident)) {
-      Diag(IdentLoc, diag::err_expected_namespace_name) << SS.getRange();
+      }
+    } else {
+      unsigned DiagID = isa<NamespaceDecl>(PrevDecl)
+                            ? diag::err_redefinition
+                            : diag::err_redefinition_different_kind;
+      Diag(AliasLoc, DiagID) << Alias;
+      Diag(PrevDecl->getLocation(), diag::note_previous_definition);
       return nullptr;
     }
   }
@@ -8315,6 +8316,8 @@ Decl *Sema::ActOnNamespaceAliasDef(Scope *S,
     NamespaceAliasDecl::Create(Context, CurContext, NamespaceLoc, AliasLoc,
                                Alias, SS.getWithLocInContext(Context),
                                IdentLoc, R.getFoundDecl());
+  if (PrevDecl)
+    AliasDecl->setPreviousDecl(cast<NamespaceAliasDecl>(PrevDecl));
 
   PushOnScopeChains(AliasDecl, S);
   return AliasDecl;