[wpiutil] Return wpi::expected from MemoryBuffer::GetFile (#7069)

wpiutil/src/main/native/thirdparty/llvm/cpp/llvm/MemoryBuffer.cpp

@@ -259,10 +259,14 @@ static std::unique_ptr<WritableMemoryBuffer> GetMemoryBufferForStream(
   return GetMemBufferCopyImpl(buffer, bufferName, ec);
 }
 
-std::unique_ptr<MemoryBuffer> MemoryBuffer::GetFile(std::string_view filename,
-                                                    std::error_code& ec,
-                                                    int64_t fileSize) {
-  return GetFileAux<MemoryBuffer>(filename, ec, fileSize, fileSize, 0);
+wpi::expected<std::unique_ptr<MemoryBuffer>, std::error_code>
+MemoryBuffer::GetFile(std::string_view filename, int64_t fileSize) {
+  std::error_code ec;
+  auto ret = GetFileAux<MemoryBuffer>(filename, ec, fileSize, fileSize, 0);
+  if (ec) {
+    return wpi::unexpected{ec};
+  }
+  return ret;
 }
 
 template <typename MB>

wpiutil/src/main/native/thirdparty/llvm/include/wpi/MemoryBuffer.h

@@ -24,6 +24,7 @@
 #include <span>
 #include <string_view>
 #include <system_error>
+#include <wpi/expected>
 
 // Duplicated from fs.h to avoid a dependency
 namespace fs {
@@ -77,9 +78,8 @@ class MemoryBuffer {
   /// if successful, otherwise returning null. If FileSize is specified, this
   /// means that the client knows that the file exists and that it has the
   /// specified size.
-  static std::unique_ptr<MemoryBuffer> GetFile(std::string_view filename,
-                                               std::error_code& ec,
-                                               int64_t fileSize = -1);
+  static wpi::expected<std::unique_ptr<MemoryBuffer>, std::error_code>
+  GetFile(std::string_view filename, int64_t fileSize = -1);
 
   /// Read all of the specified file into a MemoryBuffer as a stream
   /// (i.e. until EOF reached). This is useful for special files that