Merge processing of sdkconfig options

[stc1988]

I have a question about the How sdkconfig files are processed section.

When sdkconfig files are specified for both the application and the device, are they both merged?
For example, in the case of building the giphy app with esp32/m5stack_cores3.

[stc1988]

@phoddie
Hi, could you please take a look at this question when possible? Thanks!

[phoddie]

Good question. Because SDKCONFIG is a variable in the manifest, it can only have a single value. So, I would expect that the last value assigned to it will be the SDKCONFIG that is merged.

[stc1988]

Thank you for your response.
Does that mean that when SDKCONFIG settings are defined on the device side, like in esp32/m5stack_core, they cannot be changed from the application side?

[phoddie]

Depending on the order of evaluation (I don't remember at the moment), it means that either the application or platform is used, but not both. Either way, it someone loses.

Looking at the implementation in mcmanifest.js the SDKCONFIGPATH variable is intended to be used by the "application' so, strictly speaking, it is the platform that is misusing the variable.

To solve this, we have a couple of choices:

1. Add another variable which is for the platform. That would mostly mean duplicating the code in mcmanifest.js linked to above. That should work here. It will fail if there is another module, for example, that wants to contribute to the SDKCONFIG too.
2. Implement an SDKCONFIG array in the ESP32 section of the manifest. This would allow be an unrestricted number of contributors to SDKCONFIG. That would be similar to the "dependency" manifest section that supports the ESP Component Registry.

(1) is easy. (2) is some work.

[stc1988]

Thank you for the explanation. I understand your intention.

(2) seems straightforward, but at present, it seems that cases where it’s actually needed are quite rare.

[phoddie]

The cases are rare today, but that may be because the mechanism doesn't exist. If it did, maybe it would be used more. ;)