[yaml2obj] - Don't crash on invalid document.

Previously jaml2obj would segfault on empty document.
(without yaml description).
Patch fixes the issue.

Differential revision: https://reviews.llvm.org/D38036

llvm-svn: 313746

llvm/include/llvm/Support/YAMLTraits.h

@@ -1418,8 +1418,8 @@ inline typename std::enable_if<has_MappingTraits<T, EmptyContext>::value,
                                Input &>::type
 operator>>(Input &yin, T &docMap) {
   EmptyContext Ctx;
-  yin.setCurrentDocument();
-  yamlize(yin, docMap, true, Ctx);
+  if (yin.setCurrentDocument())
+    yamlize(yin, docMap, true, Ctx);
   return yin;
 }
 

llvm/test/Object/yaml2obj-invalid.yaml

@@ -0,0 +1,2 @@
+# RUN: not yaml2obj %s 2>&1 | FileCheck %s
+# CHECK: Unknown document type!