Fix up typo in tryTo<> for enums

Summary: This diff fixes the typo in `tryTo` declaration for `enum`s and adds test coverage for enum specialization.

Reviewed By: yfeldblum, shixiao

Differential Revision: D8694574

fbshipit-source-id: d20e34d7d7bae7805cc7c31507cffb292235bdfc

folly/Conv.h

@@ -1561,8 +1561,8 @@ tryTo(const Src& value) {
 
 template <class Tgt, class Src>
 typename std::enable_if<
-    !std::is_convertible<Src, StringPiece>::valuea &&
-        std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value,
+    !std::is_convertible<Src, StringPiece>::value && std::is_enum<Tgt>::value &&
+        !std::is_same<Src, Tgt>::value,
     Expected<Tgt, ConversionCode>>::type
 tryTo(const Src& value) {
   using I = typename std::underlying_type<Tgt>::type;

folly/test/ConvTest.cpp

@@ -1294,3 +1294,21 @@ TEST(Conv, TryToThenWithVoid) {
   Unit u = x.value();
   (void)u;
 }
+
+TEST(conv, TryIntToUnscopedEnumAndBack) {
+  enum UnscopedEnum {
+    First = 0,
+    Second = 1,
+  };
+  EXPECT_EQ(UnscopedEnum::Second, folly::tryTo<UnscopedEnum>(1).value());
+  EXPECT_EQ(1, folly::tryTo<int>(UnscopedEnum::Second).value());
+}
+
+TEST(conv, TryIntToScopedEnumAndBack) {
+  enum class ScopedEnum {
+    First = 0,
+    Second = 1,
+  };
+  EXPECT_EQ(ScopedEnum::Second, folly::tryTo<ScopedEnum>(1).value());
+  EXPECT_EQ(1, folly::tryTo<int>(ScopedEnum::Second).value());
+}