remove a use of toAppend in ChronoParse.h

Summary: We are migrating away from `folly::to`.

Reviewed By: xavierd

Differential Revision: D45935360

fbshipit-source-id: c33f0ecb0e7b2482dd7d49a8a00f3309c17caded

eden/fs/config/FieldConverter.cpp

@@ -106,7 +106,8 @@ FieldConverter<std::chrono::nanoseconds>::fromString(
   if (result.hasValue()) {
     return result.value();
   }
-  return folly::makeUnexpected(chronoParseErrorToString(result.error()).str());
+  return folly::makeUnexpected(
+      std::string{chronoParseErrorToString(result.error())});
 }
 
 std::string FieldConverter<std::chrono::nanoseconds>::toDebugString(

eden/fs/utils/ChronoParse.cpp

@@ -143,29 +143,29 @@ ChronoParseError conversionCodeToParseError(ConversionCode code) {
 
 namespace facebook::eden {
 
-StringPiece chronoParseErrorToString(ChronoParseError error) {
+std::string_view chronoParseErrorToString(ChronoParseError error) {
   switch (error) {
     case ChronoParseError::UnknownUnit:
-      return "unknown duration unit specifier"_sp;
+      return "unknown duration unit specifier";
     case ChronoParseError::InvalidChronoUnitOrder:
-      return "duration units must be listed from largest to smallest"_sp;
+      return "duration units must be listed from largest to smallest";
     case ChronoParseError::Overflow:
-      return "overflow"_sp;
+      return "overflow";
     case ChronoParseError::EmptyInputString:
-      return "empty input string"_sp;
+      return "empty input string";
     case ChronoParseError::InvalidLeadingChar:
-      return "invalid leading character"_sp;
+      return "invalid leading character";
     case ChronoParseError::NoDigits:
-      return "no digits found in input string"_sp;
+      return "no digits found in input string";
     case ChronoParseError::NonDigitChar:
-      return "non-digit character found"_sp;
+      return "non-digit character found";
     case ChronoParseError::NonWhitespaceAfterEnd:
-      return "non-whitespace character found after end of input"_sp;
+      return "non-whitespace character found after end of input";
     case ChronoParseError::OtherError:
-      return "other error"_sp;
+      return "other error";
   }
 
-  return "unexpected error"_sp;
+  return "unexpected error";
 }
 
 Expected<std::chrono::nanoseconds, ChronoParseError> stringToDuration(

eden/fs/utils/ChronoParse.h

@@ -30,18 +30,7 @@ enum class ChronoParseError {
 /**
  * Get a human-readable string describing a ChronoParseError code.
  */
-folly::StringPiece chronoParseErrorToString(ChronoParseError error);
-
-/**
- * Append the human-readable description of a ChronoParseError to a string.
- *
- * This allows ChronoParseError arguments to be used with
- * folly::to<std::string>().
- */
-template <typename String>
-void toAppend(ChronoParseError error, String* result) {
-  toAppend(chronoParseErrorToString(error), result);
-}
+std::string_view chronoParseErrorToString(ChronoParseError error);
 
 /**
  * Parse a string to a std::chrono::nanoseconds duration.

eden/fs/utils/test/ChronoTest.cpp

@@ -18,7 +18,7 @@ using folly::StringPiece;
 TEST(Chrono, chronoErrorToString) {
   EXPECT_EQ(
       "unknown duration unit specifier",
-      folly::to<std::string>(ChronoParseError::UnknownUnit));
+      chronoParseErrorToString(ChronoParseError::UnknownUnit));
   EXPECT_EQ(
       "duration units must be listed from largest to smallest",
       chronoParseErrorToString(ChronoParseError::InvalidChronoUnitOrder));