Fail build on Kconfig warning

[rettichschnidi]

Introduction

There are many tests/samples, which issue a Kconfig warning when getting built (with certain boards). This also applies to combinations which are built in CI, as Twister currently can not fail builds on Kconfig warnings.

Problem description

Not enforcing the absence of Kconfig warnings causes them to pile up, make the devs blind to them.

For example, this makes it hard to catch the relevant (new) warnings when upgrading to a new Zephyr release downstream.

Even when running Twister for well-supported platforms such as nrf52840dk/nrf52840, and for upstream code, many build.log files contain warnings like those:

-- Including generated dts.cmake file: twister-out/nrf52840dk_nrf52840/samples/subsys/profiling/perf/sample.perf/zephyr/dts.cmake

warning: PROFILING_PERF (defined at subsys/profiling/perf/Kconfig:5) was assigned the value 'y' but
got the value 'n'. Check these unsatisfied dependencies: PROFILING_PERF_HAS_BACKEND (=n). See
http://docs.zephyrproject.org/latest/kconfig.html#CONFIG_PROFILING_PERF and/or look up
PROFILING_PERF in the menuconfig/guiconfig interface. The Application Development Primer, Setting
Configuration Values, and Kconfig - Tips and Best Practices sections of the manual might be helpful
too.


warning: PROFILING_PERF_BUFFER_SIZE (defined at subsys/profiling/perf/Kconfig:15) was assigned the
value '128' but got the value ''. Check these unsatisfied dependencies: PROFILING_PERF (=n). See
http://docs.zephyrproject.org/latest/kconfig.html#CONFIG_PROFILING_PERF_BUFFER_SIZE and/or look up
PROFILING_PERF_BUFFER_SIZE in the menuconfig/guiconfig interface. The Application Development
Primer, Setting Configuration Values, and Kconfig - Tips and Best Practices sections of the manual
might be helpful too.

Proposed change

Introduce a KCONFIG_WARNINGS_AS_ERRORS option and enabled it per default in Twister, similar to ?COMPILER_WARNINGS_AS_ERRORS.

Detailed RFC

Proposed change (Detailed)

1. Introduce KCONFIG_WARNINGS_AS_ERRORS: kconfig: Add option to fail build on warning #77529. This allows developers to opt-in, ensure their applications-of-concern build warning free.
2. Start enabling KCONFIG_WARNINGS_AS_ERRORS for certain key samples/tests to enforce warning free builds in CI
3. Add KCONFIG_WARNINGS_AS_ERRORS to twister per default, allow opt-out using the existing (and to be extended) parameter --disable-warnings-as-errors
4. Clean up opt-ins from point 2.

Dependencies

• None?

Concerns and Unresolved Questions

• When a build fails due to a Kconfig warning, the dev needs to run cmake -DCONFIG_KCONFIG_WARNINGS_AS_ERRORS=n . in the build directory before being able to running west build -t menuconfig to investigate the dependency issue.

Alternatives

• Add some kind of post-build hook to grep for ^warning: messages

[teburd]

@ranj063 might have some thoughts on this one

[koffes]

I support this suggestion. As you say, devs go blind, there is a lot of build output which should be minimized, and this can go uncaught in many CI systems.

I propose an amendment:

1. KCONFIG_UNSATISFIED_DEPENDENCIES_AS_ERRORS. This should IMO be default on, and will catch all of these assigned the value 'y' but got the value 'n'. and similar. This should never happen.

2. KCONFIG_WARNINGS_AS_ERRORS as you said. This will catch all KConfig warnings, and should be default off. Sometimes we do get potentially acceptable warnings on deprecated APIs or "debug keys are used".