Some builds failed with

 ----------------------------- Captured stderr call -----------------------------
/home/runner/work/RIOT/RIOT/cpu/native/irq_cpu.c:33: error: "__USE_GNU" redefined [-Werror]
   33 | #define __USE_GNU

-- the defines have been removed.

It's generally (according to feature_test_macros(7)) preferable to provide these defines at the command line rather than around individual includes, for any other preceding include might already have transitively included that same file without the defines around it, negating their effect.

OK, I'm leaving this rabbit hole for now. Right now we have a wild mix of files that require -std=gnuxx, C files that set _GNU_SOURCE, header files that set GNU_SOURCE (?), and all without any larger semblance of a consistent plan.

I think it would be prudent to

• consistently ifndef ... define the required properties on compilation units where it's needed
• revisit whether the GNU_SOURCE (and XOPEN_SOURCE) declarations in header files even do anything reliably (given that such a header could be included from a compilation unit that previously included the relevant headers without the declarations)

and then look at whether we really need to set anything but std=cxx on native in the first place.

(and I think this is best restarted when FreeBSD and MacOS are testable in CI, otherwise this'll be a nightmare to test)

Murdock results

❌ FAILED

f1dbc39 fixup! native: Explicitly opt in to GNUisms rather than setting std=gnu11

Artifacts

This only reflects a subset of all builds from https://ci-prod.riot-os.org. Please refer to https://ci.riot-os.org for a complete build for now.

Please squash at will an ping me when Murdock is happy. I will only need a quick look to ACK this.

I think this eneavour would need a more systematic reboot, distinguishing where we have GNUisms inside compilation units (and how to set CFLAGS for these specifically), or whether any are part of our headers (ugh). This issue probably best serves as inspiration for where to find them, or as a starting point. I can't drive this to completion right now, anyone with the energy to continue this is welcome to take anything in here they deem usable.