fix: explicitly cast unspecified chrono rep type

Blackhole can handle both signed int64 and unsigned integers,
but std::chrono representation type is long long, which may
vary depending on architecture where building occurs. Thus,
it may lead to ambiguous integer promotion when it's time
to format.

This commit does explicit cast to resolve ambiguity.

This should fix #126 and #129.

src/formatter/json.cpp

@@ -41,14 +41,19 @@ struct visitor_t {
         node.AddMember(rapidjson::StringRef(name.data(), name.size()), rapidjson::kNullType, allocator);
     }
 
-    // For `bool`, `std::int64_t`, `std::uint64_t` and `double` types.
-    template<typename T>
-    auto operator()(T value) -> void {
-        static_assert(
-            std::is_same<T, bool>::value ||
-            std::is_same<T, std::int64_t>::value ||
-            std::is_same<T, std::uint64_t>::value ||
-            std::is_same<T, double>::value, "type mismatch");
+    auto operator()(bool value) -> void {
+        node.AddMember(rapidjson::StringRef(name.data(), name.size()), value, allocator);
+    }
+
+    auto operator()(std::int64_t value) -> void {
+        node.AddMember(rapidjson::StringRef(name.data(), name.size()), value, allocator);
+    }
+
+    auto operator()(std::uint64_t value) -> void {
+        node.AddMember(rapidjson::StringRef(name.data(), name.size()), value, allocator);
+    }
+
+    auto operator()(double value) -> void {
         node.AddMember(rapidjson::StringRef(name.data(), name.size()), value, allocator);
     }
 
@@ -219,9 +224,10 @@ class json_t::inner_t::builder {
             inner.timestamp(record.timestamp(), wr);
             apply("timestamp", wr.inner.data(), wr.inner.size());
         } else {
-            apply("timestamp", std::chrono::duration_cast<
+            const auto timestamp = std::chrono::duration_cast<
                 std::chrono::microseconds
-            >(record.timestamp().time_since_epoch()).count());
+            >(record.timestamp().time_since_epoch()).count();
+            apply("timestamp", static_cast<std::int64_t>(timestamp));
         }
     }