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Date: Mon, 18 May 2020 15:56:45 +0200
To: ~alpine/devel@lists.alpinelinux.org
Subject: Disable assert statements by default?
From: =?UTF-8?Q?S=C3=B6ren?= Tempel <soeren@soeren-tempel.net>
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Hi,

This is a follow-up discussion from !7970 [0], the question that was
raised in this MR is whether or not assert statements should be disabled
by default. The recently added meson helper script (abuild-meson)
previously included the `-Db_ndebug=3Dtrue` flag to disable asserts by
default. I removed this flag for two reasons: (a) I believe further
discussion is needed and (b) if we come to consensus that this is a
good idea we should enable it for all aports through /etc/abuild.conf.
That is, to make sure that all aports get the potential benefits.

A bit of background information, the C standard library includes an
assert(3) function which aborts the program if the given assertion is
false. If the preprocessor macro NDEBUG is defined (which meson defines
if the aforementioned flag is true [1]), the assert(3) function does not
generate any code. Meson itself seems to also support disabling assert
statements in other languages, e.g. D [2].

The benefits of disabling asserts by default would be:

	* Users would not run into program crashes triggered by
	  development assert statements.
	* Would probably cause a minor size reduction.

The major drawback imho is that (at least in my experience) programmers
assume that these assert statements are always true, but never formally
proof that they are. If there exists a path which causes an assert to be
false this is a bug which should be fixed. If assert(3) doesn't generate
any code (i.e. NDEBUG is defined) this causes bugs to go unnoticed.
Depending on the specific assert statement, this may also lead to
undefined behaviour (e.g. integer overflows or memory corruptions).
Undefined behaviour should obviously be avoided and falling asserts are
much easier to debug than undefined behaviour.

For software which uses assert statements that are intentionally
reachable we can still disable them by selectively passing NDEBUG but I
wouldn't enable it unconditionally by default (not even just for meson
packages).

Thoughts?

Greetings,
S=C3=B6ren

[0]: https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/7970
[1]: https://github.com/mesonbuild/meson/blob/ab6a410426d614f95b779797f3dfb=
289eb3672d9/mesonbuild/compilers/compilers.py#L320-L323
[2]: https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/7970#not=
e_88839