force explicit conversions to desired types in generated code

upb/upb.h

@@ -90,6 +90,24 @@ UPB_INLINE bool upb_StringView_IsEqual(upb_StringView a, upb_StringView b) {
   return a.size == b.size && memcmp(a.data, b.data, a.size) == 0;
 }
 
+/** upb_*Int* conversion routines ********************************************/
+
+UPB_INLINE int32_t upb_Int32_FromI(int v) {
+  return (int32_t)v;
+}
+
+UPB_INLINE int64_t upb_Int64_FromLL(long long v) {
+  return (int64_t)v;
+}
+
+UPB_INLINE uint32_t upb_UInt32_FromU(unsigned v) {
+  return (uint32_t)v;
+}
+
+UPB_INLINE uint64_t upb_UInt64_FromULL(unsigned long long v) {
+  return (uint64_t)v;
+}
+
 #define UPB_STRINGVIEW_INIT(ptr, len) \
   { ptr, len }
 

upbc/protoc-gen-upb.cc

@@ -323,13 +323,17 @@ std::string FieldDefault(const protobuf::FieldDescriptor* field) {
       return absl::Substitute("upb_StringView_FromString(\"$0\")",
                               absl::CEscape(field->default_value_string()));
     case protobuf::FieldDescriptor::CPPTYPE_INT32:
-      return absl::StrCat(field->default_value_int32());
+      return absl::Substitute("upb_Int32_FromI($0)",
+                              field->default_value_int32());
     case protobuf::FieldDescriptor::CPPTYPE_INT64:
-      return absl::StrCat(field->default_value_int64());
+      return absl::Substitute("upb_Int64_FromLL($0ll)",
+                              field->default_value_int64());
     case protobuf::FieldDescriptor::CPPTYPE_UINT32:
-      return absl::StrCat(field->default_value_uint32());
+      return absl::Substitute("upb_UInt32_FromU($0u)",
+                              field->default_value_uint32());
     case protobuf::FieldDescriptor::CPPTYPE_UINT64:
-      return absl::StrCat(field->default_value_uint64());
+      return absl::Substitute("upb_UInt64_FromULL($0ull)",
+                              field->default_value_uint64());
     case protobuf::FieldDescriptor::CPPTYPE_FLOAT:
       return absl::StrCat(field->default_value_float());
     case protobuf::FieldDescriptor::CPPTYPE_DOUBLE: