Document the existence of inherinted weights in #[pallet::call]

[kianenigma]

This code path is not well known and not well documented. It should be explained with a simple example or similar in the documentation of pallet::call and pallet::weight.

cc @shawntabrizi @gupnik

[Cjumelin]

Hi 👋

I have came with a short description of the behavior of Inherit. Yet I am not sure where to put it

CallWeightDef::Inherited

CallWeightDef::Inherited represents a call weight definition that is inherited. This variant is used when the weight of a dispatchable function is not explicitly defined but is instead determined by its parent context, if it exist. It is particularly useful in scenarios where the weight of a dispatchable is dependent on dynamic, higher-level calculations or nested dispatchable calls.

The CallWeightDef::Inherited variant is automatically applied implicitly in the following cases:

• No Explicit Weight Attribute (does not define a #[pallet::weight($expr)])

• Developer Mode dev_mode

Code Reference:

In CallDef of substrate/frame/support/procedural/src/pallet/expand/call.rs:

match weight_attrs.len() {
    0 if inherited_call_weight.is_some() => CallWeightDef::Inherited,
}

cc @ndkazu @Krayt78

[kianenigma]

Ho Cjumelin, thanks for taking this on!

To finish the task, please do the following:

1. The objective is to document how this feature is present for developers building on top of FRAME, rather than the internals of the macro
2. Therefore, what we need to only update the documentation of pallet::call and #pallet::weight
3. Within these update, only focus on specifying what feature is available to end-users, not how it is implemented.

Please open a PR for this if clear, and we will continue there!

[Cjumelin]

Can I be assigned to it then?

[shawntabrizi]

@Cjumelin done