Add filename support to yaml::Input.

[trombonehero]

Summary

The current yaml::Input constructor takes a StringRef of data as its
first parameter, discarding any filename information that may have been
present when a YAML file was opened. Add an alterate yaml::Input
constructor that takes a MemoryBufferRef, which can have a filename
associated with it. This leads to clearer diagnostic messages.

Sponsored By: DARPA, AFRL

[trombonehero]

(previously known as D11137)

[asb]

This isn't part of LLVM I usually hack on, but I just wanted to comment to say:

1. I've manually verified this patch applies cleanly to top of tree and all checks pass
2. The patch looks good to me, and addresses the final nits from @arphaman in the previous revision. The only other changes vs the previous revision seems to be the removal of CurrentNode from the initialiser list as the field now has a default initialiser (as of rL305969).

@arphaman: are you happy with this patch now?

[arphaman]

Yep, LGTM. Thanks.

llvm/trunk/include/llvm/Support/YAMLTraits.h

 public:
   // Construct a yaml Input object from a StringRef and optional
   // user-data. The DiagHandler can be specified to provide
   // alternative error reporting.
   Input(StringRef InputContent,
         void *Ctxt = nullptr,
         SourceMgr::DiagHandlerTy DiagHandler = nullptr,
         void *DiagHandlerCtxt = nullptr);
+  Input(MemoryBufferRef Input,
+        void *Ctxt = nullptr,
+        SourceMgr::DiagHandlerTy DiagHandler = nullptr,
+        void *DiagHandlerCtxt = nullptr);
   ~Input() override;
 
   // Check if there was an syntax or semantic error during parsing.
   std::error_code error();
 
 private:
   bool outputting() override;
   bool mapTag(StringRef, bool) override;

llvm/trunk/lib/Support/YAMLTraits.cpp

 Input::Input(StringRef InputContent, void *Ctxt,
              SourceMgr::DiagHandlerTy DiagHandler, void *DiagHandlerCtxt)
     : IO(Ctxt), Strm(new Stream(InputContent, SrcMgr, false, &EC)) {
   if (DiagHandler)
     SrcMgr.setDiagHandler(DiagHandler, DiagHandlerCtxt);
   DocIterator = Strm->begin();
 }
 
+Input::Input(MemoryBufferRef Input, void *Ctxt,
+             SourceMgr::DiagHandlerTy DiagHandler, void *DiagHandlerCtxt)
+    : IO(Ctxt), Strm(new Stream(Input, SrcMgr, false, &EC)) {
+  if (DiagHandler)
+    SrcMgr.setDiagHandler(DiagHandler, DiagHandlerCtxt);
+  DocIterator = Strm->begin();
+}
+
 Input::~Input() = default;
 
 std::error_code Input::error() { return EC; }
 
 // Pin the vtables to this file.
 void Input::HNode::anchor() {}
 void Input::EmptyHNode::anchor() {}
 void Input::ScalarHNode::anchor() {}

llvm/trunk/unittests/Support/YAMLIOTest.cpp

std::string intermediate;
     FooBar& map2 = seq2[1];
     EXPECT_EQ(map1.foo, 10);
     EXPECT_EQ(map1.bar, -3);
     EXPECT_EQ(map2.foo, 257);
     EXPECT_EQ(map2.bar, 0);
   }
 }
 
+//
+// Test YAML filename handling.
+//
+static void testErrorFilename(const llvm::SMDiagnostic &Error, void *) {
+  EXPECT_EQ(Error.getFilename(), "foo.yaml");
+}
+
+TEST(YAMLIO, TestGivenFilename) {
+  auto Buffer = llvm::MemoryBuffer::getMemBuffer("{ x: 42 }", "foo.yaml");
+  Input yin(*Buffer, nullptr, testErrorFilename);
+  FooBar Value;
+  yin >> Value;
+
+  EXPECT_TRUE(!!yin.error());
+}
+
 
 //===----------------------------------------------------------------------===//
 //  Test built-in types
 //===----------------------------------------------------------------------===//
 
 struct BuiltInTypes {
   llvm::StringRef str;
   std::string stdstr;