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

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

llvm-svn: 217103

4 files changed, 11 insertions, 3 deletions

diff --git a/clang/test/Modules/Inputs/cxx-decls-imported.h b/clang/test/Modules/Inputs/cxx-decls-imported.h
index 691b374d0d8..8c1e74f17c3 100644
--- a/clang/test/Modules/Inputs/cxx-decls-imported.h
+++ b/clang/test/Modules/Inputs/cxx-decls-imported.h
@@ -44,3 +44,6 @@ typedef struct {
 } NameForLinkage2;
 auto name_for_linkage2_inner_a = NameForLinkage2::Inner();
 typedef decltype(name_for_linkage2_inner_a) NameForLinkage2Inner;
+
+namespace Aliased { extern int a; }
+namespace Alias = Aliased;
diff --git a/clang/test/Modules/Inputs/cxx-decls-merged.h b/clang/test/Modules/Inputs/cxx-decls-merged.h
index 7f2baf36ee9..86e81a9bb68 100644
--- a/clang/test/Modules/Inputs/cxx-decls-merged.h
+++ b/clang/test/Modules/Inputs/cxx-decls-merged.h
@@ -22,3 +22,6 @@ typedef struct {
 } NameForLinkage2;
 auto name_for_linkage2_inner_b = NameForLinkage2::Inner();
 typedef decltype(name_for_linkage2_inner_b) NameForLinkage2Inner;
+
+namespace Aliased { extern int b; }
+namespace Alias = Aliased;
diff --git a/clang/test/Modules/cxx-decls.cpp b/clang/test/Modules/cxx-decls.cpp
index 1fb550ba280..109306ed79d 100644
--- a/clang/test/Modules/cxx-decls.cpp
+++ b/clang/test/Modules/cxx-decls.cpp
@@ -46,6 +46,8 @@ int overrides_virtual_functions_test =
 
 void use_extern_c_function() { ExternCFunction(); }
 
+int use_namespace_alias() { return Alias::a + Alias::b; }
+
 @import cxx_decls_premerged;
 
 void use_extern_c_function_2() { ExternCFunction(); }
diff --git a/clang/test/SemaCXX/namespace-alias.cpp b/clang/test/SemaCXX/namespace-alias.cpp
index e18b58b4d44..63615ecbd35 100644
--- a/clang/test/SemaCXX/namespace-alias.cpp
+++ b/clang/test/SemaCXX/namespace-alias.cpp
@@ -35,12 +35,12 @@ namespace H {
   namespace A2 { }
 
   // These all point to A1.
-  namespace B = A1; // expected-note {{previous definition is here}}
+  namespace B = A1;
   namespace B = A1;
   namespace C = B;
-  namespace B = C;
+  namespace B = C; // expected-note {{previously defined as an alias for 'A1'}}
 
-  namespace B = A2; // expected-error {{redefinition of 'B' as different kind of symbol}}
+  namespace B = A2; // expected-error {{redefinition of 'B' as an alias for a different namespace}}
 }
 
 namespace I {