Autogenerate PDA helpers

[lorisleiva]

This part is a key missing component of the autogenerated libraries that have to be added manually.

This requires Shank to capture PDA knowledge and that we "polyfill" that feature to IDLs generated by Anchor.

See metaplex-foundation/shank#23.

I'll provide some concrete examples of generated code below.

Note that it's important for the generated helpers to allow a custom programId to be provided in case we want to override the default program used.

[lorisleiva]

The create a better devex, I think we should introduce the following type (the SDK already does).

import type { PublicKey } from '@solana/web3.js';

type Pda = PublicKey & { bump: number };

That way we can return a Pda rather than the tuple [PublicKey, number] which makes devs use [0] all the time.

Here's how to generate a Pda type.

const [publicKey, bump] = PublicKey.findProgramAddressSync(
  seeds,
  programId
);

(publicKey as Pda).bump = bump;

Note that the JS SDK currently use a class for that purpose but I don't think that'll work here because every library will end up having its own class reference which would result in an instanceof hell for some users.

export class Pda extends PublicKey {
  public readonly bump: number;

  constructor(value: PublicKeyInitData, bump: number) {
    super(value);
    this.bump = bump;
  }

  static find(programId: PublicKey, seeds: Array<Buffer | Uint8Array>): Pda {
    const [publicKey, bump] = PublicKey.findProgramAddressSync(
      seeds,
      programId
    );

    return new Pda(publicKey, bump);
  }
}

[lorisleiva]

With that in mind, here are some examples:

import { Buffer } from 'buffer'; // <- Important that we don't rely on the global Node.js Buffer for browser.

export function findMetadataPda(
  mint: PublicKey,
  programId: PublicKey = TokenMetadataProgram.publicKey
): Pda {
  const [publicKey, bump] = PublicKey.findProgramAddressSync([
    Buffer.from('metadata', 'utf8'), // <- It's a literal, Shank knows what to insert.
    programId.toBuffer(), // <- It's a "programId", we know to copy over the overridable PublicKey of the program.
    mint.toBuffer(), // <- It's a variable, we need to require it in the arguments with the right type.
  ], programId);

  (publicKey as Pda).bump = bump;

  return publicKey as Pda;
};

With more variable seeds (of different types):

import { Buffer } from 'buffer';

export function findEditionMarkerPda(
  mint: PublicKey,
  editionMarker: BN,
  programId: PublicKey = TokenMetadataProgram.publicKey
): Pda {
  const [publicKey, bump] = PublicKey.findProgramAddressSync([
    Buffer.from('metadata', 'utf8'),
    programId.toBuffer(),
    mint.toBuffer(),
    Buffer.from('edition', 'utf8'),
    Buffer.from(editionMarker.toString()),
  ], programId);

  (publicKey as Pda).bump = bump;

  return publicKey as Pda;
};

Note that the SDK actually goes one step further and require the edition number and not the editionMarker because it know how to calculate it:

import { Buffer } from 'buffer';

export function findEditionMarkerPda(
  mint: PublicKey,
  edition: BN,
  programId: PublicKey = TokenMetadataProgram.publicKey
): Pda {
  const [publicKey, bump] = PublicKey.findProgramAddressSync([
    Buffer.from('metadata', 'utf8'),
    programId.toBuffer(),
    mint.toBuffer(),
    Buffer.from('edition', 'utf8'),
    Buffer.from(edition.div(new BN(248)).toString()),
  ], programId);

  (publicKey as Pda).bump = bump;

  return publicKey as Pda;
};

But that's more difficult to do when autogenerating code.

[lorisleiva]

I think these methods could be generated directly within the account file since PDAs are account specific.

It could end up generating the same code twice (e.g. MasterEdition and Edition have the same PDA seeds) but I don't think that's too much of a problem.