[lldb][Test] Propagate llvm::yaml error message in TestFile::fromYaml

[Michael137]

Summary

Currently the test-suite would swallow the error message
on llvm::yaml::convertYAML failures.

This patch simply propagates the error string up to the caller.

Before patch:

[ RUN      ] DWARFASTParserClangTests.TestDefaultTemplateParamParsing
/Users/michaelbuch/Git/llvm-worktrees/playground/lldb/unittests/TestingSupport/Symbol/YAMLModuleTester.cpp:19: Failure
Value of: llvm::detail::TakeExpected(File)
Expected: succeeded
  Actual: failed  (convertYAML() failed: )
Assertion failed: (!HasError && "Cannot get value when an error exists!"), function getStorage, file Error.h, line 671.

After patch:

[ RUN      ] DWARFASTParserClangTests.TestDefaultTemplateParamParsing
/Users/michaelbuch/Git/llvm-worktrees/playground/lldb/unittests/TestingSupport/Symbol/YAMLModuleTester.cpp:19: Failure
Value of: llvm::detail::TakeExpected(File)
Expected: succeeded
  Actual: failed  (convertYAML() failed: wrote too much data somewhere, section offsets don't line up)
Assertion failed: (!HasError && "Cannot get value when an error exists!"), function getStorage, file Error.h, line 671.

lldb/unittests/TestingSupport/TestUtilities.cpp

std::string lldb_private::GetInputFilePath(const llvm::Twine &name) {
   llvm::sys::path::append(result, "Inputs", name);
   return std::string(result.str());
 }
 
 llvm::Expected<TestFile> TestFile::fromYaml(llvm::StringRef Yaml) {
   std::string Buffer;
   llvm::raw_string_ostream OS(Buffer);
   llvm::yaml::Input YIn(Yaml);
-  if (!llvm::yaml::convertYAML(YIn, OS, [](const llvm::Twine &Msg) {}))
-    return llvm::createStringError(llvm::inconvertibleErrorCode(),
-                                   "convertYAML() failed");
+  std::string ErrorMsg("convertYAML() failed: ");
+  if (!llvm::yaml::convertYAML(YIn, OS, [&ErrorMsg](const llvm::Twine &Msg) {
+        ErrorMsg += Msg.str();
+      }))
+    return llvm::createStringError(llvm::inconvertibleErrorCode(), ErrorMsg);
   return TestFile(std::move(Buffer));
 }
 
 llvm::Expected<TestFile> TestFile::fromYamlFile(const llvm::Twine &Name) {
   auto BufferOrError =
       llvm::MemoryBuffer::getFile(GetInputFilePath(Name), /*IsText=*/false,
                                   /*RequiresNullTerminator=*/false);
   if (!BufferOrError)
     return llvm::errorCodeToError(BufferOrError.getError());
   return fromYaml(BufferOrError.get()->getBuffer());
 }