cmake: kconfig: Preserve correct CLI assignments across re-runs

This tiny patch makes two improvements:

1. Preserve boolean (=n) assignments from command-line.

This fixes an issue where, if a symbol with `default y` were turned off
via command-line, e.g., `-DCONFIG_BOOT_BANNER=n`, a CMake re-run would
revert that symbol back to its default value.

To avoid this, the assignment should have been preserved in CMake cache
as `CLI_CONFIG_BOOT_BANNER:INTERNAL=n`. However, `kconfig.cmake` clears
unset variables from cache, and (=n) symbols become unset variables, so
an exception had to be made for them.

2. Discard invalid assignments from command-line.

Although `kconfig.cmake` takes care to discard assignments to symbols
which get unset by Kconfig, it wasn't handling the case where Kconfig
would keep the symbol but replace its value, making the CMake-cached
assignment invalid.

For example, this assignment:

   west build . -DCONFIG_PRINTK=n

could be invalidated if PRINTK were selected by, e.g., BOOT_BANNER,
producing this warning:

   PRINTK (...) was assigned the value 'n' but got the value 'y'. (...)

Still, the old value of (=n) was being cached. One way in which this was
evident was when setting an unrelated symbol in a separate invocation:

   west build . -DCONFIG_MAIN_STACK_SIZE=512

the same warning for PRINTK would show up again.

Signed-off-by: Grzegorz Swiderski <grzegorz.swiderski@nordicsemi.no>
1 file changed