[YAML] fix output incorrect format for block scalar string

Author: HerrCai0907

llvm/lib/Support/YAMLTraits.cpp

@@ -725,18 +725,18 @@ void Output::blockScalarString(StringRef &S) {
   if (!StateStack.empty())
     newLineCheck();
   output(" |");
-  outputNewLine();
 
   unsigned Indent = StateStack.empty() ? 1 : StateStack.size();
 
   auto Buffer = MemoryBuffer::getMemBuffer(S, "", false);
   for (line_iterator Lines(*Buffer, false); !Lines.is_at_end(); ++Lines) {
+    outputNewLine();
     for (unsigned I = 0; I < Indent; ++I) {
       output("  ");
     }
     output(*Lines);
-    outputNewLine();
   }
+  outputUpToEndOfLine("");
 }
 
 void Output::scalarTag(std::string &Tag) {

llvm/unittests/Support/YAMLIOTest.cpp

@@ -1273,6 +1273,36 @@ TEST(YAMLIO, TestReadWriteBlockScalarValue) {
   }
 }
 
+struct V {
+  MultilineStringType doc;
+  std::string str;
+};
+template <> struct MappingTraits<V> {
+  static void mapping(IO &io, V &v) {
+    io.mapRequired("block_scalac", v.doc);
+    io.mapRequired("scalar", v.str);
+  }
+};
+template <> struct llvm::yaml::SequenceElementTraits<V> {
+  static const bool flow = false;
+};
+TEST(YAMLIO, TestScalarAfterBlockScalar) {
+  std::vector<V> v{V{}};
+  v[0].doc.str = "Just a block\nscalar doc";
+  v[0].str = "a";
+  std::string output;
+  llvm::raw_string_ostream ostr(output);
+  Output yout(ostr);
+  yout << v;
+  EXPECT_EQ(output, R"(---
+- block_scalac:     |
+    Just a block
+    scalar doc
+  scalar:          a
+...
+)");
+}
+
 //===----------------------------------------------------------------------===//
 //  Test flow sequences
 //===----------------------------------------------------------------------===//