1 files changed, 22 insertions, 8 deletions

diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 097046d93dd..b2de0455e2a 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -7842,6 +7842,10 @@ Expected<Decl *> ASTImporter::Import(Decl *FromD) {
   if (!FromD)
     return nullptr;
 
+  // Push FromD to the stack, and remove that when we return.
+  ImportPath.push(FromD);
+  auto ImportPathBuilder =
+      llvm::make_scope_exit([this]() { ImportPath.pop(); });
 
   // Check whether there was a previous failed import.
   // If yes return the existing error.
@@ -7853,6 +7857,10 @@ Expected<Decl *> ASTImporter::Import(Decl *FromD) {
   if (ToD) {
     // If FromD has some updated flags after last import, apply it
     updateFlags(FromD, ToD);
+    // If we encounter a cycle during an import then we save the relevant part
+    // of the import path associated to the Decl.
+    if (ImportPath.hasCycleAtBack())
+      SavedImportPaths[FromD].push_back(ImportPath.copyCycleAtBack());
     return ToD;
   }
 
@@ -7889,16 +7897,20 @@ Expected<Decl *> ASTImporter::Import(Decl *FromD) {
       // FIXME: AST may contain remaining references to the failed object.
     }
 
-    // Error encountered for the first time.
-    assert(!getImportDeclErrorIfAny(FromD) &&
-           "Import error already set for Decl.");
-
-    // After takeError the error is not usable any more in ToDOrErr.
+    // After takeError the error is not usable anymore in ToDOrErr.
     // Get a copy of the error object (any more simple solution for this?).
     ImportError ErrOut;
     handleAllErrors(ToDOrErr.takeError(),
                     [&ErrOut](const ImportError &E) { ErrOut = E; });
     setImportDeclError(FromD, ErrOut);
+
+    // Set the error for all nodes which have been created before we
+    // recognized the error.
+    for (const auto &Path : SavedImportPaths[FromD])
+      for (Decl *Di : Path)
+        setImportDeclError(Di, ErrOut);
+    SavedImportPaths[FromD].clear();
+
     // Do not return ToDOrErr, error was taken out of it.
     return make_error<ImportError>(ErrOut);
   }
@@ -7921,6 +7933,7 @@ Expected<Decl *> ASTImporter::Import(Decl *FromD) {
   Imported(FromD, ToD);
 
   updateFlags(FromD, ToD);
+  SavedImportPaths[FromD].clear();
   return ToDOrErr;
 }
 
@@ -8641,9 +8654,10 @@ ASTImporter::getImportDeclErrorIfAny(Decl *FromD) const {
 }
 
 void ASTImporter::setImportDeclError(Decl *From, ImportError Error) {
-  assert(ImportDeclErrors.find(From) == ImportDeclErrors.end() &&
-         "Setting import error allowed only once for a Decl.");
-  ImportDeclErrors[From] = Error;
+  auto InsertRes = ImportDeclErrors.insert({From, Error});
+  // Either we set the error for the first time, or we already had set one and
+  // now we want to set the same error.
+  assert(InsertRes.second || InsertRes.first->second.Error == Error.Error);
 }
 
 bool ASTImporter::IsStructurallyEquivalent(QualType From, QualType To,