From: Philipp Stephani <p.stephani2@gmail.com>
To: Eli Zaretskii <eliz@gnu.org>,
aurelien.aptel+emacs@gmail.com, tzz@lifelogs.com,
dancol@dancol.org
Cc: emacs-devel@gnu.org
Subject: Re: Dynamic modules: emacs-module.c and signaling errors
Date: Wed, 25 Nov 2015 18:09:25 +0000 [thread overview]
Message-ID: <CAArVCkQuuFqXXdC_DLkMCLfT0+0CXEehX_y2-H0NCgKa80Uhzw@mail.gmail.com> (raw)
In-Reply-To: <83k2p7xk13.fsf@gnu.org>
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Eli Zaretskii <eliz@gnu.org> schrieb am Di., 24. Nov. 2015 um 20:41 Uhr:
> In "emacs -Q", load the modules/mod-test/mod-test module, then try
> this:
>
> M-: (mod-test-sum "1" 2) RET
>
> Result: Emacs aborts. This happens because the eassert in
> module_extract_integer aborts, when that function is called for the
> 2nd time:
>
> static intmax_t
> module_extract_integer (emacs_env *env, emacs_value n)
> {
> check_main_thread ();
> eassert (module_non_local_exit_check (env) ==
> emacs_funcall_exit_return);
> Lisp_Object l = value_to_lisp (n);
> if (! INTEGERP (l))
> {
> module_wrong_type (env, Qintegerp, l);
> return 0;
> }
>
> The first call to module_extract_integer correctly detects the wrong
> type of argument and calls module_wrong_type. But module_wrong_type
> just records the problem in the env structure, it doesn't signal any
> Lisp error, like an Emacs primitive would. So the actual error goes
> undetected, and is masked by the assertion violation (because Emacs is
> built with --enable-checking).
>
> Since this obviously works as it was designed, my question is: how
> should a module be written so that this kind of errors signal a normal
> Lisp error we are accustomed with Emacs primitives?
>
>
I still need to fix most of the example module (unfortunately that was
written before the error handling got implemented), but the gist is that
functions returning emacs_value should usually be called like this:
emacs_value ret = env->foo(env, ...);
if (ret == NULL) return NULL;
This will cause errors to be reported back to Emacs, where they are thrown
as normal signals.
I have thought about how we can prevent some accidental misuse. I propose
that all environment functions should have a signature like this:
__attribute__((warn_unused_result))
bool (*func)(emacs_env *env, ..., result_type* result);
instead of returning result directly. This way users get a warning if they
forget to check for errors. The above example would then turn into:
emacs_value ret;
if (!env->foo(env, ..., &ret)) return false;
which isn't worse, but avoids sentinel values and makes the API harder to
misuse. Thoughts?
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next prev parent reply other threads:[~2015-11-25 18:09 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-24 19:41 Dynamic modules: emacs-module.c and signaling errors Eli Zaretskii
2015-11-24 19:45 ` Eli Zaretskii
2015-11-24 20:12 ` Tom Tromey
2015-11-24 20:49 ` Eli Zaretskii
2015-11-24 21:34 ` Paul Eggert
2015-11-24 21:55 ` Daniel Colascione
2015-11-25 6:52 ` Paul Eggert
2015-11-25 7:03 ` Daniel Colascione
2015-11-25 7:14 ` Paul Eggert
2015-11-25 7:18 ` Daniel Colascione
2015-11-25 7:23 ` Paul Eggert
2015-11-25 7:25 ` Daniel Colascione
2015-11-25 7:49 ` Paul Eggert
2015-11-25 7:52 ` Daniel Colascione
2015-11-25 7:58 ` Paul Eggert
2015-11-25 8:12 ` Daniel Colascione
2015-11-25 8:24 ` Paul Eggert
2015-11-25 8:50 ` Daniel Colascione
2015-11-25 9:11 ` Daniel Colascione
2015-11-25 18:19 ` Eli Zaretskii
2015-11-25 18:26 ` Philipp Stephani
2015-11-25 19:19 ` Eli Zaretskii
2015-11-25 21:52 ` Philipp Stephani
2015-11-25 17:34 ` Paul Eggert
2015-11-24 22:21 ` Tom Tromey
2015-11-25 6:55 ` Paul Eggert
2015-11-25 17:30 ` Eli Zaretskii
2015-11-25 17:34 ` Paul Eggert
2015-11-25 21:23 ` Stefan Monnier
2015-11-26 15:42 ` Eli Zaretskii
2015-11-26 16:36 ` Stefan Monnier
2015-11-26 17:08 ` Eli Zaretskii
2015-11-26 19:28 ` Stefan Monnier
2015-11-26 19:34 ` Eli Zaretskii
2015-11-26 20:11 ` Stefan Monnier
2015-11-26 20:19 ` Eli Zaretskii
2015-11-26 21:20 ` Paul Eggert
2015-11-26 22:29 ` Philipp Stephani
2015-11-26 22:33 ` Philipp Stephani
2015-11-27 1:06 ` Stefan Monnier
2015-11-27 1:10 ` Daniel Colascione
2015-11-27 15:06 ` Stefan Monnier
2015-11-27 8:12 ` Eli Zaretskii
2015-11-27 9:11 ` Eli Zaretskii
2015-11-27 12:25 ` Aurélien Aptel
2015-11-27 14:44 ` Eli Zaretskii
2015-11-28 23:31 ` Paul Eggert
2015-11-27 1:21 ` Stefan Monnier
2015-11-27 8:26 ` Eli Zaretskii
2015-11-27 15:15 ` Stefan Monnier
2015-11-27 15:57 ` Eli Zaretskii
2015-11-27 16:29 ` Stefan Monnier
2015-11-27 17:38 ` Eli Zaretskii
2015-11-27 17:54 ` Stefan Monnier
2015-11-25 18:10 ` Tom Tromey
2015-11-25 18:15 ` Eli Zaretskii
2015-11-25 18:09 ` Philipp Stephani [this message]
2015-11-25 21:19 ` Stefan Monnier
2015-11-26 15:41 ` Eli Zaretskii
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