Regression: `cfunction return type struct fields cannot contain a reference`

[pablosanjose]

I get this error on v1.8 beta1 (not on 1.7.2), both under Intel and M1 macos, whenever I wrap a type containing a heap reference.

MWE:

julia> using FunctionWrappers: FunctionWrapper

julia> struct T
           x::Vector{Int}
       end

julia> FunctionWrapper{T,Tuple{}}(() -> T([1,2]))
ERROR: cfunction return type struct fields cannot contain a reference
Stacktrace:
 [1] macro expansion
   @ ~/.julia/packages/FunctionWrappers/8xdVB/src/FunctionWrappers.jl:83 [inlined]
 [2] gen_fptr
   @ ~/.julia/packages/FunctionWrappers/8xdVB/src/FunctionWrappers.jl:81 [inlined]
 [3] FunctionWrapper{T, Tuple{}}(obj::var"#1#2")
   @ FunctionWrappers ~/.julia/packages/FunctionWrappers/8xdVB/src/FunctionWrappers.jl:100
 [4] top-level scope
   @ REPL[3]:1

julia> versioninfo()
Julia Version 1.8.0-beta1
Commit 7b711ce699 (2022-02-23 15:09 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin18.7.0)
  CPU: 8 × Intel(R) Core(TM) i7-5775R CPU @ 3.30GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-13.0.1 (ORCJIT, broadwell)
  Threads: 1 on 8 virtual cores
Environment:
  JULIA_EDITOR = code