bug#74879: 30.0.92; trusted-content-p and trusted-files cannot be used for non-file buffers

[Daniel Mendler via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> Thank you for the recent addition of `trusted-content-p'. Is there a
>> possibility to use `trusted-content-p' in buffers which are not backed
>> by a file? I use Flymake in *scratch* or similar buffers and it seems
>> that this won't continue to work given that `trusted-content-p' needs a
>> `buffer-file-truename'.
>
> Good question.
> We don't really have a good answer yet, AFAIK, in large part because we
> don't have enough experience with it.
> Off the top of my head, here are some elements relevant to this
> discussion, in random order:
>
> - The current setup is a kind of "minimal" change for Emacs-30 because
>   it's late in the pretest, so as much as possible we should separate
>   the discussion into what's a simple enough solution for Emacs-30 and
>   what we should use in the longer term.

Agree. As I suggested a simple trusted-buffer-function hook may be the
simplest solution, which is also not limiting and allows us to mark
various buffers as trusted.

> - You should be able to get fully-featured Flymake in *scratch*
>   with (setq-local trusted-files :all).
>   Maybe we should do that when we setup *scratch*?
>   Which other non-file buffers would need that?  The minibuffer?

Given that the trust applies to the given buffer, setting `(setq-local
trusted-files :all)' in this buffer feels odd as a recommended
mechanism. Even more so since the variable is marked as risky local.

> - Trust sucks, so we really should work on better solutions where we
>   don't need to rely on trust, such as running code in `bwrap` or other
>   kinds of sandboxes.

I agree. But what about interactive scenarios like auto completion?
There we may be limited to trust, even if we want sandboxing in other
scenarios. I think trust checking might be helpful in all scenarios
where there is a "low threshold" to invoking code execution or even
unintentionally.

> - I think we do want some kind of hook, with which we can have (for
>   instance) `emacs-lisp-mode` tell Emacs to trust the user init file,
>   the early-init file, the custom-file, and all the files in
>   `load-path`.

You suggest a hook which is executed per buffer? This seems similar to
my proposal of a trusted-buffer-function hook.

Daniel