meson: Ignore unused variables in release builds

Variables that are only used for assertions are considered unused in release builds. Don't treat this as an error, since we build with -Werror even for release in CI. This causes reasonable code to build and pass tests locally (and therefore to be queued for merge by reasonable developers), but later fail in CI due to a variable used only as an assertion. This pattern is common enough we have an ASSERTED macro to workaround the behaviour, but failing a CI run to have the author go back and add in the ASSERTED and re-queue later is a recipe for frustration, wasted time, and wasted CI bandwidth.

Disable this behaviour to reduce CI friction.

In my view, sprinkling in ASSERTED clutters the code, rather than helps; I find CI's insistence on doing so actively counterproductive. Developers are free to continue doing so after this change. But this way CI won't fail merge requests over it. After all, CI enforces policy, and we shouldn't have "mark variables only used for assertions as ASSERTED" as policy. Let's pick our battles wisely and improve CI's signal-to-noise ratio.

Note that actual unused variables will be caught by debug builds. It is expected that develpers do debug builds locally before ramming code through CI, so that should be caught.

RFC: Should -Wunused-function also be silenced for release (but not debug) builds? This affects a similar case of assert(some_validation()).

Signed-off-by: Alyssa Rosenzweig alyssa@collabora.com Suggested-by: Daniel Stone daniels@collabora.com