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Properly fix Jump out of too many nested blocks error #20

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c5a1271
Properly fix `Jump out of too many nested blocks` error
insignification Dec 10, 2019
8b431a2
Rename new SyntaxError to be more descriptive in case ever encountered.
Dec 10, 2019
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68 changes: 41 additions & 27 deletions goto.py
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Original file line number Diff line number Diff line change
Expand Up @@ -86,6 +86,19 @@ def _parse_instructions(code):
extended_arg_offset = None
yield (dis.opname[opcode], oparg, offset)

def _get_instruction_size(opname, oparg=0):
size = 1

extended_arg = oparg >> _BYTECODE.argument_bits
if extended_arg != 0:
size += _get_instruction_size('EXTENDED_ARG', extended_arg)
oparg &= (1 << _BYTECODE.argument_bits) - 1

opcode = dis.opmap[opname]
if opcode >= _BYTECODE.have_argument:
size += _BYTECODE.argument.size

return size

def _write_instruction(buf, pos, opname, oparg=0):
extended_arg = oparg >> _BYTECODE.argument_bits
Expand Down Expand Up @@ -164,37 +177,38 @@ def _patch_code(code):
target_depth = len(target_stack)
if origin_stack[:target_depth] != target_stack:
raise SyntaxError('Jump into different block')

size = 0
for i in range(len(origin_stack) - target_depth):
size += _get_instruction_size('POP_BLOCK')
size += _get_instruction_size('JUMP_ABSOLUTE', target // _BYTECODE.jump_unit)

moved_to_end = False
if pos + size > end:
# not enough space, add at end
pos = _write_instruction(buf, pos, 'JUMP_ABSOLUTE', len(buf) // _BYTECODE.jump_unit)

if pos > end:
raise SyntaxError('Goto in an incredibly huge function') # not sure if reachable

size += _get_instruction_size('JUMP_ABSOLUTE', end // _BYTECODE.jump_unit)

moved_to_end = True
pos = len(buf)
buf.extend([0] * size)

failed = False
try:
for i in range(len(origin_stack) - target_depth):
pos = _write_instruction(buf, pos, 'POP_BLOCK')

if target >= end:
rel_target = (target - pos) // _BYTECODE.jump_unit
oparg_bits = 0

while True:
rel_target -= (1 + _BYTECODE.argument.size) // _BYTECODE.jump_unit
if rel_target >> oparg_bits == 0:
pos = _write_instruction(buf, pos, 'EXTENDED_ARG', 0)
break

oparg_bits += _BYTECODE.argument_bits
if rel_target >> oparg_bits == 0:
break

pos = _write_instruction(buf, pos, 'JUMP_FORWARD', rel_target)
else:
pos = _write_instruction(buf, pos, 'JUMP_ABSOLUTE', target // _BYTECODE.jump_unit)

except (IndexError, struct.error):
failed = True

if failed or pos > end:
raise SyntaxError('Jump out of too many nested blocks')

_inject_nop_sled(buf, pos, end)
pos = _write_instruction(buf, pos, 'JUMP_ABSOLUTE', target // _BYTECODE.jump_unit)
except (IndexError, struct.error) as e:
raise SyntaxError("Internal error", e)

if moved_to_end:
pos = _write_instruction(buf, pos, 'JUMP_ABSOLUTE', end // _BYTECODE.jump_unit)

else:
_inject_nop_sled(buf, pos, end)

return _make_code(code, _array_to_bytes(buf))

Expand Down
120 changes: 72 additions & 48 deletions test_goto.py
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Original file line number Diff line number Diff line change
Expand Up @@ -71,63 +71,87 @@ def func():

pytest.raises(SyntaxError, with_goto, func)

if sys.version_info >= (3, 6):
def test_jump_out_of_nested_2_loops():
@with_goto
def func():
x = 1
for i in range(2):
for j in range(2):
# These are more than 256 bytes of bytecode, requiring
# a JUMP_FORWARD below on Python 3.6+, since the absolute
# address would be too large, after leaving two blocks.
x += x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x
x += x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x
x += x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x
def test_jump_out_of_nested_2_loops():
@with_goto
def func():
x = 1
for i in range(2):
for j in range(2):
# These are more than 256 bytes of bytecode
x += x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x
x += x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x
x += x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x

goto .end
label .end
return (i, j)

assert func() == (0, 0)

def test_jump_out_of_nested_3_loops():
@with_goto
def func():
for i in range(2):
for j in range(2):
for k in range(2):
goto .end
label .end
return (i, j)
label .end
return (i, j, k)

assert func() == (0, 0)
assert func() == (0, 0, 0)

def test_jump_out_of_nested_3_loops():
def func():
for i in range(2):
for j in range(2):
for k in range(2):
def test_jump_out_of_nested_4_loops():
@with_goto
def func():
for i in range(2):
for j in range(2):
for k in range(2):
for m in range(2):
goto .end
label .end
return (i, j, k)

pytest.raises(SyntaxError, with_goto, func)
else:
def test_jump_out_of_nested_4_loops():
@with_goto
def func():
for i in range(2):
for j in range(2):
for k in range(2):
for m in range(2):
goto .end
label .end
return (i, j, k, m)
label .end
return (i, j, k, m)

assert func() == (0, 0, 0, 0)
assert func() == (0, 0, 0, 0)

def test_jump_out_of_nested_5_loops():
def func():
for i in range(2):
for j in range(2):
for k in range(2):
for m in range(2):
for n in range(2):
goto .end
label .end
return (i, j, k, m, n)
def test_jump_out_of_nested_5_loops():
@with_goto
def func():
for i in range(2):
for j in range(2):
for k in range(2):
for m in range(2):
for n in range(2):
goto .end
label .end
return (i, j, k, m, n)

pytest.raises(SyntaxError, with_goto, func)
assert func() == (0, 0, 0, 0, 0)

def test_jump_out_of_nested_11_loops():
@with_goto
def func():
x = 1
for i1 in range(2):
for i2 in range(2):
for i3 in range(2):
for i4 in range(2):
for i5 in range(2):
for i6 in range(2):
for i7 in range(2):
for i8 in range(2):
for i9 in range(2):
for i10 in range(2):
for i11 in range(2):
# These are more than 256 bytes of bytecode
x += x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x
x += x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x
x += x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x+x

goto .end
label .end
return (i1, i2, i3, i4, i5, i6, i7, i8, i9, i10, i11)

assert func() == (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)

def test_jump_across_loops():
def func():
Expand Down