That sounds cool, but this quickly gets complicated. Some aspects that need to be addressed:

- where does the automatically defined struct live? Data segment might work for static, but doesn't allow dynamic use. Stack will be garbage if closure outlives function context (ie. callback, future). Heap might work, but how do you prevent leaks without C++/Rust RAII?

- while a function pointer may be copied or moved, the state area probably cannot. It may contain pointers to stack object or point into itself (think Rust's pinning)

- you already mention recursion, compilation

- ...

IMO the C way is to allow users to explicitly manage context area, along the lines of posix ucontext.h or how the author's closure proposal handle closure allocation[1]. [1] https://thephd.dev/_vendor/future_cxx/papers/C%20-%20Functio...