bug#31229: 27.0.50; Semantic mode for Python causes segmentation fault

[Glenn Morris]

Stuart wrote:

> Emacs segfaults when semantic-mode is enabled in a python buffer. To
> reproduce this, place the python code below into a file. I called it
> the_file.py'.
> Then run 'emacs -Q the_file.py', then 'M-x semantic-mode'.
>
> Here's the contents of a file that emacs crashes on:
>
> import sys
> import re
>
> def foo(x):
>     print(x)
>     print("Hello world!")
>
> def bar(x):
>     print("I'm a teapot")
>
> class emacs_bug:
>
>     def __init__():
>         pass
>

Confirmed on RHEL 7.4 (clicking around the menu bar triggers it for me).
Crashes at lread.c:1777.
Reverting f939cd0 fixes it.