gh-89726 handle frame.f_lineno is None in inspect.getframeinfo

[graingert]

https://bugs.python.org/issue45563

• Issue: inspect.getframeinfo() doesn't handle frames without lineno #89726

[graingert]

there's a lasti2lineno implementation here - but it uses a reversed list(dis.finelinestarts(code)) and starts at 0 instead of co_firstlineno

cpython/Lib/pdb.py

Lines 119 to 126 in deeaac4

	def lasti2lineno(code, lasti):
	linestarts = list(dis.findlinestarts(code))
	linestarts.reverse()
	for i, lineno in linestarts:
	if lasti >= i:
	return lineno
	return 0

[markshannon]

What are you trying to fix here?

[graingert]

What are you trying to fix here?

frame can sometimes have a frame.f_lineno=None and so inspect.getframeinfo fails eg:

import sys
import inspect

def demo():
    for i in range(1):
        if i >= 0:
            pass


class Tracer:
    def __init__(self):
        self.events = []

    def trace(self, frame, event, arg):
        inspect.getframeinfo(frame)
        frame.f_trace_lines = True
        frame.f_trace_opcodes = True
        return self.trace

def main():
    t = Tracer()
    old_trace = sys.gettrace()
    try:
        sys.settrace(t.trace)
        demo()
    finally:
        sys.settrace(old_trace)


if __name__ == "__main__":
    sys.exit(main())

Traceback (most recent call last):
  File "/home/graingert/projects/cpython/demo.py", line 31, in <module>
    sys.exit(main())
  File "/home/graingert/projects/cpython/demo.py", line 25, in main
    demo()
  File "/home/graingert/projects/cpython/demo.py", line -1, in demo
  File "/home/graingert/projects/cpython/demo.py", line -1, in demo
  File "/home/graingert/projects/cpython/demo.py", line 15, in trace
    inspect.getframeinfo(frame)
  File "/usr/lib/python3.10/inspect.py", line 1627, in getframeinfo
    start = lineno - 1 - context//2
TypeError: unsupported operand type(s) for -: 'NoneType' and 'int'

[markshannon]

I would make more sense IMO to fix inspect to not crash, rather than trying to fake a line number.