Change isset field from bool to uint8_t

Summary:
We want to replace `isset` from `bool` to `bit` and we will do it step by step. So in this diff, we will replace `isset` from `bool` to `uint_8` and update related code.

- It will replace:
```
 struct Foo {
 private:
  struct __isset {
    bool field1;
    bool field2;
    // ...
    bool field9;

    bool __fbthrift_get (folly::index_constant<0>) const {
        return field1 ;
    }
    bool __fbthrift_get (folly::index_constant<1>) const {
        return field1;
    }
   ...

    bool __fbthrift_get (folly::index_constant<8>) const {
        return field9;
    }

    void __fbthrift_set (folly::index_constant<0>, bool isset_flag) const {
        field1 = isset_flag;
        return;
    }
    void __fbthrift_set (folly::index_constant<1>, bool isset_flag) const {
        field2 = isset_flag;
        return;
    }
    ...

    void __fbthrift_set (folly::index_constant<8>, bool isset_flag) const {
        field9 = isset_flag;
        return;
    }

  } __isset = {};
  // ...
};
```
with:
```
 struct Foo {
 private:
  struct __isset {
    uint_8 field1;
    uint_8 field2;
    // ...
    uint_8 field9;

    bool __fbthrift_get (folly::index_constant<0>) const {
        return field1 == 1;
    }
    bool __fbthrift_get (folly::index_constant<1>) const {
        return field1 == 1;
    }
   ...

    bool __fbthrift_get (folly::index_constant<8>) const {
        return field9 == 1;
    }

    void __fbthrift_set (folly::index_constant<0>, bool isset_flag) const {
        field1 = isset_flag ? 1 : 0;;
    }
    void __fbthrift_set (folly::index_constant<1>, bool isset_flag) const {
        field2 = isset_flag ? 1 : 0;;
    }
    ...

    void __fbthrift_set (folly::index_constant<8>, bool isset_flag) const {
        field9 = isset_flag ? 1 : 0;;
    }

  } __isset = {};
  // ...
};
```
- Add new functions `make_optional_field_ref` and `make_field_ref` in detail namespace, and replace `optional_field_ref` and `field_ref` with these new functions.

Next steps:
- Change multiple isset fields into a single array of uint8_t
- Compress array of uint8_t into bits.
- Change isset struct into bitset.

Reviewed By: Mizuchi

Differential Revision: D30523019

fbshipit-source-id: 8d1060f89af560c9a5e707cba88dea0c2903d0f7

mcrouter/lib/carbon/ReplyCommon.h

@@ -9,6 +9,7 @@
 
 #include <memory>
 
+#include <thrift/lib/cpp2/FieldRef.h>
 #include "mcrouter/lib/carbon/MessageCommon.h"
 #include "mcrouter/lib/carbon/gen-cpp2/carbon_result_types.h"
 
@@ -49,17 +50,19 @@ class ReplyCommonThrift : public ReplyCommon {
     return result_;
   }
 
-  apache::thrift::field_ref<const carbon::Result&> result_ref() const& {
-    return {this->result_, __isset.result};
+  auto result_ref() const& {
+    return apache::thrift::detail::make_field_ref(
+        this->result_, __isset.result);
   }
 
-  apache::thrift::field_ref<carbon::Result&> result_ref() & {
-    return {this->result_, __isset.result};
+  auto result_ref() & {
+    return apache::thrift::detail::make_field_ref(
+        this->result_, __isset.result);
   }
 
  private:
   struct __isset {
-    bool result;
+    uint8_t result;
   } __isset = {};
   carbon::Result result_{carbon::Result::UNKNOWN};
 };

mcrouter/lib/carbon/test/a/b/gen/BMessages.h

@@ -84,7 +84,7 @@ class SimpleStruct {
 
  private:
   struct __isset {
-    bool member1;
+    uint8_t member1;
   } __isset = {};
 
   int64_t member1_{0};
@@ -275,7 +275,7 @@ class YetAnotherRequest : public carbon::RequestCommon {
 
  private:
   struct __isset {
-    bool key;
+    uint8_t key;
   } __isset = {};
 
   carbon::Keys<folly::IOBuf> key_;
@@ -326,7 +326,7 @@ class YetAnotherReply : public carbon::ReplyCommon {
 
  private:
   struct __isset {
-    bool result;
+    uint8_t result;
   } __isset = {};
 
   carbon::Result result_{carbon::Result::UNKNOWN};

mcrouter/lib/carbon/test/a/gen/AMessages.h

@@ -88,7 +88,7 @@ class AnotherRequest : public carbon::RequestCommon {
 
  private:
   struct __isset {
-    bool key;
+    uint8_t key;
   } __isset = {};
 
   carbon::Keys<folly::IOBuf> key_;
@@ -139,7 +139,7 @@ class AnotherReply : public carbon::ReplyCommon {
 
  private:
   struct __isset {
-    bool result;
+    uint8_t result;
   } __isset = {};
 
   carbon::Result result_{carbon::Result::UNKNOWN};

mcrouter/lib/carbon/test/b/gen/BMessages.h

@@ -76,7 +76,7 @@ class BaseStruct {
 
  private:
   struct __isset {
-    bool baseInt64Member;
+    uint8_t baseInt64Member;
   } __isset = {};
 
   int64_t baseInt64Member_{0};
@@ -208,11 +208,11 @@ class SimpleStruct {
 
  private:
   struct __isset {
-    bool _carbon_basestruct_;
-    bool int32Member;
-    bool stringMember;
-    bool enumMember;
-    bool vectorMember;
+    uint8_t _carbon_basestruct_;
+    uint8_t int32Member;
+    uint8_t stringMember;
+    uint8_t enumMember;
+    uint8_t vectorMember;
   } __isset = {};
 
   BaseStruct _carbon_basestruct_;