1 files changed, 21 insertions, 0 deletions
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 59539566e7d..d102cdf55dd 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -10144,6 +10144,27 @@ TypedefDecl *Sema::ParseTypedefDecl(Scope *S, Declarator &D, QualType T,
     if (!Context.hasSameType(T, Context.getTagDeclType(tagFromDeclSpec)))
       break;
 
+    // If we've already computed linkage for the anonymous tag, then
+    // adding a typedef name for the anonymous decl can change that
+    // linkage, which might be a serious problem.  Diagnose this as
+    // unsupported and ignore the typedef name.  TODO: we should
+    // pursue this as a language defect and establish a formal rule
+    // for how to handle it.
+    if (tagFromDeclSpec->hasLinkageBeenComputed()) {
+      Diag(D.getIdentifierLoc(), diag::err_typedef_changes_linkage);
+
+      SourceLocation tagLoc = D.getDeclSpec().getTypeSpecTypeLoc();
+      tagLoc = Lexer::getLocForEndOfToken(tagLoc, 0, getSourceManager(),
+                                          getLangOpts());
+
+      llvm::SmallString<40> textToInsert;
+      textToInsert += ' ';
+      textToInsert += D.getIdentifier()->getName();
+      Diag(tagLoc, diag::note_typedef_changes_linkage)
+        << FixItHint::CreateInsertion(tagLoc, textToInsert);
+      break;
+    }
+
     // Otherwise, set this is the anon-decl typedef for the tag.
     tagFromDeclSpec->setTypedefNameForAnonDecl(NewTD);
     break;