Bugfix: grpc supress incorrect warning

[fliiiix]

new_p is a local addr but is owned now by slice_
thus the life time does not end at the end of the function

The newest compilers had opinions about returning new_p here.

[fliiiix]

@aardappel should be easy to merge, maybe there would be a way to rewrite this to be simpler for humans and compiler but it wasn't clear to me how

[aardappel]

It doesn't seem so great to be putting compiler specific warning toggles in the code like this.

What is the exact error? Can it be fixed in different ways, for example to construct the slice directly in slice_ such that there is no new_slice to warn about? Or to make the assignment between the two a move operation so it is clear to the compiler the local is not in use anymore? etc.

[fliiiix]

The error/warning message with GCC 14.3 is:

src/vendor/flatbuffers/include/flatbuffers/grpc.h: In member function ‘virtual uint8_t* flatbuffers::grpc::SliceAllocator::reallocate_downward(uint8_t*, size_t, size_t, size_t, size_t)’:
src/vendor/flatbuffers/include/flatbuffers/grpc.h:124:12: warning: function may return address of local variable [-Wreturn-local-addr]
  124 |     return new_p;
      |            ^~~~~
src/vendor/flatbuffers/include/flatbuffers/grpc.h:119:19: note: declared here
  119 |     ::grpc::Slice new_slice = ::grpc::Slice(new_size);
      |                   ^~~~~~~~~

I updated the MR to return the pointer to the _slice.begin() which should be the same as new_p and allowing the compiler to understand that the address is not out of scope

[aardappel]

Hmm this seems strange that this is required for the compiler, but I guess we'll merge for now.

[fliiiix]

Thanks, I assume at some point diagnostics will become better but for now i guess the compiler sees the pointer and new_slice and both are going out of scope and it misses the fact that this memory is now owned by slice_

[mustiikhalil]

Sorry was reading from the phone and miss clicked

[fliiiix]

@aardappel i don't think any failed CI jobs are related to this change?