core/thread_flags: remove #error from header file

[jia200x]

Contribution description

This commit removes the #error from the thread_flags header.
This #error makes the usage of
if(IS_USED(MODULE_THAT_DEPENDS_ON_THREAD_FLAGS)) pattern harder,
because the error is triggered each time the header is included.
If a module uses any thread_flags function it will fail in link time
anyway.

Testing procedure

Try removing the core_thread_flags dependency from any component that requires thread flags (e.g /tests/thread_flags_xtimer. It should fail.

Issues/PRs references

#13669

[kaspar030]

This #error makes the usage of
if(IS_USED(MODULE_THAT_DEPENDS_ON_THREAD_FLAGS)) pattern harder,
because the error is triggered each time the header is included.

don't include headers you don''t use?

[miri64]

This #error makes the usage of
if(IS_USED(MODULE_THAT_DEPENDS_ON_THREAD_FLAGS)) pattern harder,
because the error is triggered each time the header is included.

don't include headers you don''t use?

This leads to a lot of ugly #ifdefs if the module is used optionally.

[jia200x]

This leads to a lot of ugly #ifdefs if the module is used optionally.

This.

You need to add the header files for that pattern:

#include "A.h"

if (IS_USED(MODULE_A)) {
    function_in_header_a();
}
another_function();

It will fail if you didn't include "A.h" header.

[kaspar030]

This leads to a lot of ugly #ifdefs if the module is used optionally.

This.

Yes, but as soon as we add static inline thread_flags_get() { return sched_active_thread->thread_flags; } because it is useful, you have to make the define conditional anyways. I'm sorry your macro breaks.

[jia200x]

Yes, but as soon as we add static inline thread_flags_get() { return sched_active_thread->thread_flags; } because it is useful, you have to make the define conditional anyways. I'm sorry your macro breaks.

Well, the function doesn't exist now, right? And as soon as someone add it, you only need to guard the function instead of a whole snippet of code. That's what it was done in #13669

[miri64]

Yes, but as soon as we add static inline thread_flags_get() { return sched_active_thread->thread_flags; } because it is useful, you have to make the define conditional anyways. I'm sorry your macro breaks.

Then we introduce that like this:

static inline thread_flags_t thread_flags_get()
{
#if IS_USED(MODULE_CORE_THREAD_FLAGS)
    return sched_active_thread->thread_flags;
#else
    return 0U;
#endif
}

[kaspar030]

ACK.

[bergzand]

And go!