Pretty print for interface::Result

Summary:
- Add a pretty-print interface for interface::Result so we don't have to manually unpack it to print the error code & message
- Use uint8_t as the underlying type for error codes

Reviewed By: pbhandar2

Differential Revision: D90684997

fbshipit-source-id: 6da8e72bc5cdd471b05443eede29a2d1b6f8a59b

Author: rlyerly

cachelib/cachebench/runner/CacheComponentStressor.cpp

@@ -104,9 +104,7 @@ CacheComponentStressor::CacheComponentStressor(
 
   auto cache =
       RAMCacheComponent::create(std::move(lruConfig), std::move(poolConfig));
-  XCHECK(cache.hasValue())
-      << "Error code: " << static_cast<int8_t>(cache.error().code_) << ": "
-      << cache.error().error_;
+  XCHECK(cache.hasValue()) << cache.error();
   cache_ = std::make_unique<RAMCacheComponent>(std::move(cache).value());
 }
 

cachelib/interface/Result.h

@@ -18,10 +18,13 @@
 
 #include <folly/Expected.h>
 
+#include <magic_enum/magic_enum.hpp>
+
 namespace facebook::cachelib::interface {
 
 struct Error {
-  enum class Code {
+  enum class Code : uint8_t {
+    // User errors
     INVALID_ARGUMENTS,
     INVALID_CONFIG,
 
@@ -60,3 +63,12 @@ using Result = folly::Expected<Value, Error>;
 using UnitResult = Result<folly::Unit>;
 
 } // namespace facebook::cachelib::interface
+
+namespace std {
+inline ostream& operator<<(ostream& os,
+                           const facebook::cachelib::interface::Error& error) {
+  os << "Error (" << magic_enum::enum_name(error.code_) << ", code "
+     << static_cast<uint8_t>(error.code_) << "): " << error.error_;
+  return os;
+}
+} // namespace std