Detect malformed YAML sequence in yaml::Input::beginSequence()

When reading a yaml::SequenceTraits object, YAMLIO does not report an
error if the yaml item is not a sequence. Instead, YAMLIO reads an
empty sequence. For example:

---
seq:
    foo: 1
    bar: 2
...

If `seq` is a SequenceTraits object, then reading the above yaml will
yield `seq` as an empty sequence.

Fix this to report an error for the above mapping ("not a sequence")

Patch by William Fisher. Thanks!

llvm-svn: 230976

1 files changed, 10 insertions, 7 deletions

diff --git a/llvm/lib/Support/YAMLTraits.cpp b/llvm/lib/Support/YAMLTraits.cpp
index 43a0e102d7e..d888e698937 100644
--- a/llvm/lib/Support/YAMLTraits.cpp
+++ b/llvm/lib/Support/YAMLTraits.cpp
@@ -168,9 +168,17 @@ void Input::endMapping() {
 }
 
 unsigned Input::beginSequence() {
-  if (SequenceHNode *SQ = dyn_cast<SequenceHNode>(CurrentNode)) {
+  if (SequenceHNode *SQ = dyn_cast<SequenceHNode>(CurrentNode))
     return SQ->Entries.size();
+  if (isa<EmptyHNode>(CurrentNode))
+    return 0;
+  // Treat case where there's a scalar "null" value as an empty sequence.
+  if (ScalarHNode *SN = dyn_cast<ScalarHNode>(CurrentNode)) {
+    if (isNull(SN->value()))
+      return 0;
   }
+  // Any other type of HNode is an error.
+  setError(CurrentNode, "not a sequence");
   return 0;
 }
 
@@ -192,12 +200,7 @@ void Input::postflightElement(void *SaveInfo) {
   CurrentNode = reinterpret_cast<HNode *>(SaveInfo);
 }
 
-unsigned Input::beginFlowSequence() {
-  if (SequenceHNode *SQ = dyn_cast<SequenceHNode>(CurrentNode)) {
-    return SQ->Entries.size();
-  }
-  return 0;
-}
+unsigned Input::beginFlowSequence() { return beginSequence(); }
 
 bool Input::preflightFlowElement(unsigned index, void *&SaveInfo) {
   if (EC)