bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands

[João Távora]

Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Fri, 1 Oct 2021 17:10:57 +0000
>> From: Alan Mackenzie <acm@muc.de>
>> 
>> In emacs -Q in the emacs-28 branch, create the following two line file,
>> foobar.el, and try to load it:
>> 
>> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>> (defvar foo-baz "foobar-baz")
>> FOOBARELISP-SHORTHANDS: (("foo" . "foobar")))
>> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>> 
>> This will throw an error, but that isn't important.
>> 
>> What is important is that the symbol foobar-baz is created by the
>> elisp-shorthands facility.
>> 
>> This shouldn't happen since:
>> 1/- There is no Local Variables section.
>> 2/- There is no variable elisp-shorthands in that non-existent section.
>> 
>> The following errors are evident in hack-elisp-shorthands:
>> 1/- The code doesn't check for a correctly formatted Local Variables
>>   section.
>> 2/- The code, even if it did check, would only check the last 3000 bytes
>>   in the file.  The section can occur anywhere in the last 3000
>>   CHARACTERS.
>> 3/- The code doesn't do a case-sensitive search for "elisp-shorthands".
>> 4/- The code doesn't check for "elisp-shorthands" being a complete
>>   symbol.
>> 5/- The code doesn't even check that "elisp-shorthands" is in a comment.
>
> Thanks.
>
> João, could you please look into this?

Done.  In the Emacs 28 branch.  All tests pass (except a strange
'seccomp' one that never did).  Let me know if some more bugs lurk.

Addressed all the points except the last one which doesn't make much
sense, since normal `hack-local-variables` also doesn't do any such
check.  In fact what I'm doing is re-using
hack-local-variables--find-variables from files.el, as I had wanted to
anyway.

João