dis failed to parse function that has only annotations

[uriyyo]

BPO	42562
Nosy	@markshannon, @uriyyo
PRs	bpo-42562: Fix issue when dis failed to parse function that has no line numbers #23632

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-12-04.15:23:45.704>
created_at = <Date 2020-12-03.20:38:17.926>
labels = ['type-bug', 'library', '3.10']
title = 'dis failed to parse function that has only annotations'
updated_at = <Date 2020-12-04.15:23:45.703>
user = 'https://github.com/uriyyo'

bugs.python.org fields:

activity = <Date 2020-12-04.15:23:45.703>
actor = 'Mark.Shannon'
assignee = 'none'
closed = True
closed_date = <Date 2020-12-04.15:23:45.704>
closer = 'Mark.Shannon'
components = ['Library (Lib)']
creation = <Date 2020-12-03.20:38:17.926>
creator = 'uriyyo'
dependencies = []
files = []
hgrepos = []
issue_num = 42562
keywords = ['patch']
message_count = 4.0
messages = ['382453', '382477', '382491', '382493']
nosy_count = 2.0
nosy_names = ['Mark.Shannon', 'uriyyo']
pr_nums = ['23632']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42562'
versions = ['Python 3.10']

[uriyyo]

dis module failed when trying to parse function that has only annotations at the function body:

def foo():
    a: int

Failed with stacktrace:

  1           0 LOAD_CONST               0 (<code object foo at 0x10847ebe0, file "test.py", line 1>)
              2 LOAD_CONST               1 ('foo')
              4 MAKE_FUNCTION            0
              6 STORE_NAME               0 (foo)
              8 LOAD_CONST               2 (None)
             10 RETURN_VALUE

Disassembly of <code object foo at 0x10847ebe0, file "test.py", line 1>:
Traceback (most recent call last):
  File "/Users/yuriikarabas/my-projects/temp-cpython/Lib/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/Users/yuriikarabas/my-projects/temp-cpython/Lib/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/Users/yuriikarabas/my-projects/temp-cpython/Lib/dis.py", line 536, in <module>
    _test()
  File "/Users/yuriikarabas/my-projects/temp-cpython/Lib/dis.py", line 533, in _test
    dis(code)
  File "/Users/yuriikarabas/my-projects/temp-cpython/Lib/dis.py", line 79, in dis
    _disassemble_recursive(x, file=file, depth=depth)
  File "/Users/yuriikarabas/my-projects/temp-cpython/Lib/dis.py", line 381, in _disassemble_recursive
    _disassemble_recursive(x, file=file, depth=depth)
  File "/Users/yuriikarabas/my-projects/temp-cpython/Lib/dis.py", line 373, in _disassemble_recursive
    disassemble(co, file=file)
  File "/Users/yuriikarabas/my-projects/temp-cpython/Lib/dis.py", line 369, in disassemble
    _disassemble_bytes(co.co_code, lasti, co.co_varnames, co.co_names,
  File "/Users/yuriikarabas/my-projects/temp-cpython/Lib/dis.py", line 389, in _disassemble_bytes
    maxlineno = max(linestarts.values()) + line_offset
ValueError: max() arg is an empty sequence

[markshannon]

There are two issues here.

1. The compiler is not following PEP-626 for functions with no executable code
2. dis is not robust in the case that there are no line numbers.

I want to fix 1. first, then 2.

[markshannon]

New changeset f24b810 by Yurii Karabas in branch 'master':
bpo-42562: Fix issue when dis failed to parse function that has no line numbers (GH-23632)
f24b810

[markshannon]

Thanks Yurii