cmake: add REQUIRED option ot dt_nodelabel

[unsanded]

dt_nodelabel ea currently fail quietly.
This can cause some very confusing errors later on. By adding REQUIRED to the function call one can easily generate a more clear message:

required nodelabel not found: ...

I wrote this because i spent an hour debugging a strange error, which was caused because my dts didn't have a slot0_partition nodelabel, which mcuboot expects.

[tejlmand]

Fine extension for cases where a nodelabel, alias, or property is indeed required.

But I would not go as far as saylng that a missing nodelabel, alias, or property is a quiet failure today.
Ref:

• dt_nodelabel
• dt_alias
• dt_prop

these currently fail quietly.

There are many valid use-cases where a label can be missing which should not cause a failure, and it is documented that in those cases, the return variable will be empty so the caller of the function does have the ability to check for that:

zephyr/cmake/modules/extensions.cmake

Line 3635 in 34727df

# <var> will be undefined if node does not exist.

zephyr/cmake/modules/extensions.cmake

Lines 3682 to 3683 in 34727df

	# The node's path will be returned in the <var> parameter. The
	# variable will be left undefined if the alias does not exist.

But having a REQUIRED option for cases where the label / property is required is a fine addition and can avoid boilerplate testing code for developers.

Just a minor observation to fix before a final +1.

[tejlmand]

please remove extra empty line.

Suggested change

[tejlmand]

and remember to fix compliance.

[unsanded]

Thanks for the review, i fixed the compliance and the line :)
Btw, the reason (and an example usecase) for this was: here. I didn't have this nodelabel, on my board (arduino nano ble), but the error only came way down in dt_prop, since path was empty.

[tejlmand]

Btw, the reason (and an example usecase) for this was: here.

Thanks, and exactly that use seems to be flawed in MCUboot here:
https://github.com/zephyrproject-rtos/mcuboot/blob/84b56b61118a1140e1afcb8802e2d94dd9fee44d/boot/zephyr/CMakeLists.txt#L371-L376

where ERROR is used instead of FATAL_ERROR.
If the correct FATAL_ERROR had been used there, my expectation is that you had found your missing node much earlier.

So it seems it is mcuboot which silently fail because it failed to properly handle missing nodes.

[tejlmand]

sent a patch to mcuboot here: mcu-tools/mcuboot#2065

[unsanded]

I agree the flaw was in mcuboot. I was going to send them a patch, but then it seemed that having this option would be the least duplicated code way, hence this pull request.