[ASTImporter] Fix name conflict handling with different strategies

There are numorous flaws about the name conflict handling, this patch
attempts fixes them. Changes in details:

* HandleNameConflict return with a false DeclarationName

Hitherto we effectively never returned with a NameConflict error, even
if the preceding StructuralMatch indicated a conflict.
Because we just simply returned with the parameter `Name` in
HandleNameConflict and that name is almost always `true` when converted to
`bool`.

* Add tests which indicate wrong NameConflict handling

* Add to ConflictingDecls only if decl kind is different

Note, we might not indicate an ODR error when there is an existing record decl
and a enum is imported with same name.  But there are other cases. E.g. think
about the case when we import a FunctionTemplateDecl with name f and we found a
simple FunctionDecl with name f. They overload.  Or in case of a
ClassTemplateDecl and CXXRecordDecl, the CXXRecordDecl could be the 'templated'
class, so it would be false to report error.  So I think we should report a
name conflict error only when we are 100% sure of that.  That is why I think it
should be a general pattern to report the error only if the kind is the same.

* Fix failing ctu test with EnumConstandDecl

In ctu-main.c we have the enum class 'A' which brings in the enum
constant 'x' with value 0 into the global namespace.
In ctu-other.c we had the enum class 'B' which brought in the same name
('x') as an enum constant but with a different enum value (42). This is clearly
an ODR violation in the global namespace. The solution was to rename the
second enum constant.

 * Introduce ODR handling strategies

Reviewers: a_sidorin, shafik

Differential Revision: https://reviews.llvm.org/D59692

llvm-svn: 370045

1 files changed, 4 insertions, 4 deletions

diff --git a/clang/test/Analysis/Inputs/ctu-other.c b/clang/test/Analysis/Inputs/ctu-other.c
index 9a952061102..82d29c6edb3 100644
--- a/clang/test/Analysis/Inputs/ctu-other.c
+++ b/clang/test/Analysis/Inputs/ctu-other.c
@@ -12,11 +12,11 @@ int f(int i) {
 }
 
 // Test enums.
-enum B { x = 42,
-         l,
-         s };
+enum B { x2 = 42,
+         y2,
+         z2 };
 int enumCheck(void) {
-  return x;
+  return x2;
 }
 
 // Test reporting an error in macro definition