Eli Zaretskii <eliz@gnu.org> schrieb am Mo., 9. Okt. 2017 um 08:54 Uhr:

> From: Philipp Stephani <p.stephani2@gmail.com>
> Date: Sun, 08 Oct 2017 23:14:18 +0000
> Cc: eggert@cs.ucla.edu, emacs-devel@gnu.org
>
> Jansson only accepts UTF-8 strings, and at least in our usage will also only hand out UTF-8 strings.

How can we be 100% sure of that? We don't trust any other libraries
with such high fidelity, we always decode any external data.

We also trust glibc's malloc to never return overlapping non-freed blocks, right? This "trust" isn't different. Of course we can assume that libraries behave according to their specification.

> It's totally OK to rely on this assumption since all code that's involved here is part of the Emacs core, so it can
> rely on implementation details.

That is in stark contrast with your usual coding style, which tends to
place checks and assertions where they are not always needed.

I wouldn't mind placing an assertion here as well. An assertion primarily documents the assumptions made in the code and as a side effect is also tested in debug builds. It's generally a good idea to add such documentation.

Could
it be that you underestimate the damage that broken non-ASCII byte
stream can cause Emacs if inserted directly into a buffer or a string?
Doing so will usually cause Emacs die a horrible death quite soon,
because code that processes buffer or string text has no defenses
against such calamities.

If and when such a bug happens, we can work around it (after filing a bug against Jansson). But we can't work around potential bugs in libraries, see above.