feat: r/demo/foo20airdrop - Merkle Airdrop contract example

[albttx]

Description

This PR bring an example for a merkle airdrop contract.

• the package p/demo/airdrop
• the realm r/demo/foo20airdrop

How it's works ?

A merkle airdrop contract works by saving off-chain the elements of the merkle tree. ONLY the Merkle root is saved on the realm.

To confirm an element is present, we just need to send to the contract a merkle proof.

[albttx]

waiting for: #893 and #895 to undraft

[moul]

For better control and data integrity, keep the fields in the Airdrop struct unexported.

To maintain easy marshaling with the Bytes helper, consider this approach:

type Airdrop struct {
    data struct {
        Address std.Address
        Amount  uint64
    }
}

[zivkovicmilos]

Looks good 💯

Please see @moul's comments, otherwise we should be good to go

[moul]

Just blocking since there are several changes. Let’s make an additional round of reviews.

[albttx]

There is tests issue once rebased with master.

There is a situation to figure out, with grc20.IGRC20, because it return a grc20.UserToken .

When user1.gno -> r/foo20-airdrop get foo20.GRC20() and then from r/foo20-airdrop exec foo20.GRC20().Transfert, std.PrevRealm isn't the realm but the user ...

Possible fix could be to update in user_token.gno to use CurrentRealm rather than PrevRealm

[moul]

Related (and depending?) on #952

[zivkovicmilos]

Hey @albttx,

What's the status of this PR?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.95%. Comparing base (628f965) to head (245b432).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #906      +/-   ##
==========================================
- Coverage   60.96%   60.95%   -0.02%     
==========================================
  Files         564      564              
  Lines       75273    75273              
==========================================
- Hits        45893    45885       -8     
- Misses      26009    26019      +10     
+ Partials     3371     3369       -2     

Flag	Coverage Δ
contribs/gnodev	61.46% <ø> (ø)
contribs/gnofaucet	14.46% <ø> (ø)
gno.land	67.92% <ø> (ø)
gnovm	65.78% <ø> (ø)
misc/genstd	80.54% <ø> (ø)
misc/logos	19.88% <ø> (ø)
tm2	62.04% <ø> (-0.09%)	⬇️

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[thinhnx-var]

Excuse me, can you let me know the current status of this idea @albttx ?

[albttx]

It was blocked by #1257 for a long time, i just realized it has been merged!

I'll fixup this PR :)