Matter Code generation questions

[BertL]

Currently the Matter code generation process is a bit confusing to me. Part of the code needs to be generated before building, using west zap-generate. Another part of the code is generated during the build process. Why is this necessary? Wouldn't it make more sense to generate everything during the build process, so we only need the zap-file as input?

A bit more information in the documentation would also be useful in my opinion. For instance:

• What is the difference between the .zap and .matter file? Do you need both? Which one do you need when?
• Is it always okay to just use west zap-generate or is it sometimes necessary to also use west zap-generate --full?
• Does the zap file determine which Matter version is going to be used (using the featureLevel value)?

[Maria Gilje]

Hello,

What is the difference between the .zap and .matter file? Do you need both? Which one do you need when?

Here is some documentation which covers .zap and .matter files: https://project-chip.github.io/connectedhomeip-doc/zap_and_codegen/code_generation.html 

Is it always okay to just use west zap-generate or is it sometimes necessary to also use west zap-generate --full?

I can see that the argument is listed as an option for west zap-generate, but it is not in our documentation for west zap-generate. I can't find any internal documentation where it is used either, so I think it is not relevant for nRF Connect SDK. 

Does the zap file determine which Matter version is going to be used (using the featureLevel value)?

To my understanding, no. The Matter version is determined by the SDK version, see the full overview in the togglable table in the Matter launch documentation page. The ZAP tool also needs to be the corresponding version, but this is handled for you when using west zap-gui from a Matter sample directory within the SDK. 

Best regards,

Maria