Support Python 3.8 decompilation

[zrax]

Tasks

• Bytecode support (pycdas)
• Handle new opcodes in AST builder
  • BEGIN_FINALLY
  • END_ASYNC_FOR
  • CALL_FINALLY
  • POP_FINALLY

[TiZCrocodile]

@zrax do you have an idea how to support the new while loops?
because I don't see a way to infer a comparison of a while, just until the JUMP_ABSOLUTE or JUMP_BACKWARD or JUMP_BACKWARD_IF_TRUE etc. which is already the end of the while loop.

so we would need to maybe switch the if block inferred before to a while?
or maybe go over all the opcodes before we process them, as a pre step to search for a while loops?
for example this source code:

item = None
while item is None:
    print('inside while')

has this bytecode in 3.7:

  2           0 LOAD_CONST               0 (None)
              2 STORE_FAST               0 (item)

  3           4 SETUP_LOOP              20 (to 26)
        >>    6 LOAD_FAST                0 (item)
              8 LOAD_CONST               0 (None)
             10 COMPARE_OP               8 (is)
             12 POP_JUMP_IF_FALSE       24

  4          14 LOAD_GLOBAL              0 (print)
             16 LOAD_CONST               1 ('inside while')
             18 CALL_FUNCTION            1
             20 POP_TOP
             22 JUMP_ABSOLUTE            6
        >>   24 POP_BLOCK
        >>   26 LOAD_CONST               0 (None)
             28 RETURN_VALUE

whereas in 3.8, it's exactly the same only there is no SETUP_LOOP and POP_BLOCK, so the only thing here that differentiate it from a regular if statement, is the JUMP_ABSOLUTE or any other opcode that goes backwards like this. what way do you think we can solve this maybe?