FFI backlog

[quasilyte]

This issue lists features that are nice to have but are not implemented in our FFI yet.

Separate issues can be created for any of these.

Important

• [ ] Variable-size arrays support. We have fixed-size arrays and pointers, but there is currently no way to create a T[$n].
• [ ] Pointer dereferencing via $ptr[0] syntax
• [ ] Array indexing operations (read+write) via $array[$i] syntax (we have it for fixed-size arrays, but not for dynamic arrays)
• [x] FFI::string function
• [ ] Preserve const information in TypeData; should it be a ffi_const_flag_e bit or something more complex? Can we store FFIType* there and avoid all the headaches (this will ease the arrays support too)? #357

Less important

• Add support for calling C function ptr that were returned from C code (e.g. c2php for functions)
• Add support for PHP function passing and calling it from C code (e.g. php2c for functions and closures)
• Compile-time checks for FFI::cast(T1, T2) where sizeof(T1) > sizeof(T2). PHP throws exception in that case.

Even less important

• Detect obviously bad (close to UB) patterns that cause segfault even in PHP. For example, $v = FFI::cdef('struct Foo { int32_t x; };')->new('struct Foo'); var_dump($v); will cause a segfault in PHP8.
• Add a check for "Attempt to perform assign pointer to owned C data" (see PHP sources)