Update metadata.md

[wheresaddie]

updated to 0x0c

[danforbes]

Apparently this is the actual change to the transaction encoding (?) that caused the version bump paritytech/substrate#6969 I'm not sure if this change has been incorporated into our docs.

[wheresaddie]

good to know. In that case might run this by @folsen or @gnunicorn ..?

[gnunicorn]

@thiolliere should be able to say.

[gui1117]

below in the doc is explained each field of module metadata: name, storage, error, ... but not index.

An explanation is that index is:

index comes from how pallet is defined in construct_runtime. For example:

construct_runtime!(
...
{
Pallet: my_pallet::{...}, // index is implicitly 0
MySecondPallet: my_second_pallet::{..} = 2, // index is explicitly 2
MyOtherPallet: my_other_pallet::{..}, // index is implicitly 3 (same rules as rust fieldless enum 
}
)

I'm not sure it is interesting to go into such details, just saying it is the index assigned in construct_runtime seems enough.

About the change to the transaction encoding, this document doesn't explain it here, but maybe another document covers it ?

The encoding change is this: before:

construct_runtime!(
...
{
Pallet: my_pallet::{Event}, // the variant for Pallet event in the runtime event is at index 0
MySecondPallet: my_second_pallet::{Call}, // the variant for MySecondPallet call in the runtime call is at index 0
MyOtherPallet: my_other_pallet::{Call, Event}, // the variant for MyOtherPallet call in the runtime call is at index 1 and event at index 1
}
)

and now

construct_runtime!(
...
{
Pallet: my_pallet::{Event}, // the variant for Pallet event in the runtime event is at index 0
MySecondPallet: my_second_pallet::{Call}, // the variant for MySecondPallet call in the runtime call is at index 1
MyOtherPallet: my_other_pallet::{Call, Event}, // the variant for MyOtherPallet call in the runtime call is at index 2 and event at index 2
}
)

i.e. for Event, Call and Origin the index for the corresponding variant is the index of the pallet.

[danforbes]

Is this still relevant or was it superseded by #718?