1 files changed, 10 insertions, 2 deletions
diff --git a/llvm/lib/Support/YAMLTraits.cpp b/llvm/lib/Support/YAMLTraits.cpp
index ae7f7dcb0d0..1a6adbf559b 100644
--- a/llvm/lib/Support/YAMLTraits.cpp
+++ b/llvm/lib/Support/YAMLTraits.cpp
@@ -510,8 +510,16 @@ void Output::endBitSetScalar() {
 
 void Output::scalarString(StringRef &S) {
   this->newLineCheck();
-  if (S.find('\n') == StringRef::npos) {
-    // No embedded new-line chars, just print string.
+
+  if (S.empty()) {
+    // Print '' for the empty string because leaving the field empty is not
+    // allowed.
+    this->outputUpToEndOfLine("''");
+    return;
+  }
+  if (!strchr("'`@\"", S.front()) && S.find('\n') == StringRef::npos) {
+    // Plain string cannot start with double quote or single quote. Backquote
+    // and atsign are reserved characters. Newline is not allowed.
     this->outputUpToEndOfLine(S);
     return;
   }