There has been discussion about whether invocations of optional API
that has been disabled should:
1. result in a link-time error because the API implementation is not
provided; or
2. result in a run-time error by having a trivial implementation that
returns -ENOTSUP.
Clarify that the intent of the guideline is that a link-time error
should be produced. The rationale is that it is too easy to disable
the option at build time, and not discover it because the application
fails to check for a `-ENOTSUP` return.
Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
Various API involves functions and data that are conditionally
enabled. Zephyr practice is to exclude data (always) and function
(sometimes) declarations at build time using the enabling preprocessor
macro. This meets functional needs, but blocks generation of the API
documentation as Doxygen will not see the declarations.
Document the need to extend Doxygen's PREDEFINED setting to generate
the documentation.
Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
Provide a location for recommended practices that are not related to
coding style. Initialize it with information about the expected
design for callbacks.
Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
