idl: Fix using Pubkey constants with seeds::program

[acheroncrypto]

Problem

Using Pubkey constants with seeds::program:

const PUBKEY_CONST: Pubkey = pubkey!("4LVUJzLugULF1PemZ1StknKJEEtJM6rJZaGijpNqCouG");

#[derive(Accounts)]
pub struct PubkeyConst<'info> {
    #[account(
        seeds = [],
        seeds::program = PUBKEY_CONST,
        bump
    )]
    pub acc: UncheckedAccount<'info>,
}

results in the following compile error:

error[E0277]: the trait bound `std::vec::Vec<u8>: From<anchor_lang::prelude::Pubkey>` is not satisfied
   --> programs/pda-derivation/src/lib.rs:233:10
    |
233 | #[derive(Accounts)]
    |          ^^^^^^^^ the trait `From<anchor_lang::prelude::Pubkey>` is not implemented for `std::vec::Vec<u8>`
    |
    = help: the following other types implement trait `From<T>`:
              `std::vec::Vec<u8>` implements `From<&str>`
              `std::vec::Vec<u8>` implements `From<ByteString>`
              `std::vec::Vec<u8>` implements `From<CString>`
              `std::vec::Vec<u8>` implements `From<std::string::String>`
    = note: required for `anchor_lang::prelude::Pubkey` to implement `Into<std::vec::Vec<u8>>`
    = note: this error originates in the derive macro `Accounts` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0277`.
error: could not compile `pda-derivation` (lib test) due to 1 previous error
Error: Building IDL failed. Run `ANCHOR_LOG=true anchor idl build` to see the logs.

This is because we don't have a reliable way to decide the seed expression's actual type inside macros. As a workaround, the IDL generation assumes the type to be Pubkey if the identifier ends with ID:

anchor/lang/syn/src/idl/accounts.rs

Lines 369 to 378 in fa38102

	// Not all types can be converted to `Vec<u8>` with `.into` call e.g. `Pubkey`.
	// This is problematic for `seeds::program` but a hacky way to handle this
	// scenerio is to check whether the last segment of the path ends with `ID`.
	let seed = path
	.path
	.segments
	.last()
	.filter(|seg| seg.ident.to_string().ends_with("ID"))
	.map(|_| quote! { #seed.as_ref() })
	.unwrap_or_else(|| quote! { #seed });

However, this means if people don't append the ID suffix, it likely won't compile (e.g. #3558).

Summary of changes

Fix using Pubkey constants with seeds::program in IDL generation by using AsRef::<[u8]>::as_ref before using Into::into.

Fixes #3558

[vercel]

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