test: fix undefined order of functio parameters. (#6946)

Detected instability when built `flatbuffers-2.0.0` on `gcc-12`:

    [ 75%] Building CXX object CMakeFiles/flattests.dir/tests/test_builder.cpp.o
    .../c++/12.0.0/bits/shared_ptr_base.h:397:45: error: 'size' may be used uninitialized [-Werror=maybe-uninitialized]
      397 |       explicit _Sp_ebo_helper(_Tp&& __tp) : _M_tp(std::move(__tp)) { }
          |                                             ^~~~~~~~~~~~~~~~~~~~~~
    In file included from flatbuffers/tests/test_builder.cpp:1:
    flatbuffers/tests/test_builder.h: In function 'void builder_move_assign_after_releaseraw_test(Builder) [with Builder = flatbuffers::FlatBufferBuilder]':
    flatbuffers/tests/test_builder.h:63:10: note: 'size' was declared here
       63 |   size_t size, offset;
          |          ^~~~
    ...
    In file included from flatbuffers/tests/test_builder.cpp:1:
    flatbuffers/tests/test_builder.h: In function 'void builder_move_assign_after_releaseraw_test(Builder) [with Builder = GrpcLikeMessageBuilder]':
    flatbuffers/tests/test_builder.h:63:10: note: 'size' was declared here
       63 |   size_t size, offset;
          |          ^~~~
    cc1plus: all warnings being treated as errors

Here is the relevant bit of test:

    template<class Builder>
    void builder_move_assign_after_releaseraw_test(Builder b1) {
      auto root_offset1 = populate1(b1);
      b1.Finish(root_offset1);
      size_t size, offset;
      std::shared_ptr<uint8_t> raw(
          b1.ReleaseRaw(size, offset), [size](uint8_t *ptr) {
            flatbuffers::DefaultAllocator::dealloc(ptr, size);
          });

Note how `b1.ReleaseRaw(size, offset)` is expected to populate `size`
and `[size](uint8_t *ptr) {` captures the result. But both are parameters
to the same function call and thus evaluation order is unspecified.

diff --git a/tests/test_builder.h b/tests/test_builder.h
index 6d97ac0..75338b0 100644 (file)
--- a/tests/test_builder.h
+++ b/tests/test_builder.h
@@ -61,8 +61,10 @@ void builder_move_assign_after_releaseraw_test(Builder b1) {
   auto root_offset1 = populate1(b1);
   b1.Finish(root_offset1);
   size_t size, offset;
+
+  uint8_t *rr = b1.ReleaseRaw(size, offset);
   std::shared_ptr<uint8_t> raw(
-      b1.ReleaseRaw(size, offset), [size](uint8_t *ptr) {
+      rr, [size](uint8_t *ptr) {
         flatbuffers::DefaultAllocator::dealloc(ptr, size);
       });
   Builder src;