[Modules] Implement ODR-like semantics for tag types in C/ObjC

Allow ODR for ObjC/C in the sense that we won't keep more that
one definition around (merge them). However, ensure the decl
pass the structural compatibility check in C11 6.2.7/1, for that,
reuse the structural equivalence checks used by the ASTImporter.

Few other considerations:
- Create error diagnostics for tag types mismatches and thread
them into the structural equivalence checks.
- Note that by doing this we only support redefinition between types
that are considered "compatible types" by C.

This is mixed approach of the suggestions discussed in
http://lists.llvm.org/pipermail/cfe-dev/2017-March/053257.html

Differential Revision: https://reviews.llvm.org/D31778

rdar://problem/31909368

llvm-svn: 306918

1 files changed, 12 insertions, 7 deletions

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 06a9d70..0705454 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -4319,8 +4319,15 @@ void Parser::ParseEnumSpecifier(SourceLocation StartLoc, DeclSpec &DS,
     return;
   }
 
-  if (Tok.is(tok::l_brace) && TUK != Sema::TUK_Reference)
-    ParseEnumBody(StartLoc, TagDecl);
+  if (Tok.is(tok::l_brace) && TUK != Sema::TUK_Reference) {
+    Decl *D = SkipBody.CheckSameAsPrevious ? SkipBody.New : TagDecl;
+    ParseEnumBody(StartLoc, D);
+    if (SkipBody.CheckSameAsPrevious &&
+        !Actions.ActOnDuplicateDefinition(DS, TagDecl, SkipBody)) {
+      DS.SetTypeSpecError();
+      return;
+    }
+  }
 
   if (DS.SetTypeSpecType(DeclSpec::TST_enum, StartLoc,
                          NameLoc.isValid() ? NameLoc : StartLoc,
@@ -4392,11 +4399,9 @@ void Parser::ParseEnumBody(SourceLocation StartLoc, Decl *EnumDecl) {
     }
 
     // Install the enumerator constant into EnumDecl.
-    Decl *EnumConstDecl = Actions.ActOnEnumConstant(getCurScope(), EnumDecl,
-                                                    LastEnumConstDecl,
-                                                    IdentLoc, Ident,
-                                                    attrs.getList(), EqualLoc,
-                                                    AssignedVal.get());
+    Decl *EnumConstDecl = Actions.ActOnEnumConstant(
+        getCurScope(), EnumDecl, LastEnumConstDecl, IdentLoc, Ident,
+        attrs.getList(), EqualLoc, AssignedVal.get());
     EnumAvailabilityDiags.back().done();
 
     EnumConstantDecls.push_back(EnumConstDecl);