mint:: account constraint does not work

[EP-u-NW]

I'm trying to init a mint account and then mint to an associated token account, but my code won't compile.

I'm using anchor 0.20.1, below is my code:

use crate::program::Example;
use anchor_lang::prelude::*;
use anchor_spl::{
    associated_token::AssociatedToken,
    token::{Mint, Token, TokenAccount},
};

declare_id!("Fg6PaFpoGXkYsidMpWTK6W2BeZ7FEfcYkg476zPFsLnS");

#[program]
pub mod example {
    use super::*;
    pub fn mint_request(ctx: Context<MintRequest>) -> ProgramResult {
        Ok(())
    }
}

#[derive(Accounts)]
pub struct MintRequest<'info> {
    #[account(
        init,
        payer = minter,
        // I'd like my program as authority
        // and since mint::authority = <target_account>,
        // and per documentation target_account needs to be
        // part of this struct, I introduced this_program.
        mint::authority = this_program,
        mint::decimals = 0,
    )]
    pub mint_account: Account<'info, Mint>,
    #[account(
        init,
        payer = minter,
        associated_token::mint=mint_account,
        associated_token::authority = minter,
    )]
    pub token: Account<'info, TokenAccount>,
    #[account(mut)]
    pub minter: Signer<'info>,
    pub system_program: Program<'info, System>,
    pub token_program: Program<'info, Token>,
    pub associated_token_program: Program<'info, AssociatedToken>,
    pub this_program: Program<'info, Example>,
}

The problem seems to be #[derive(Accounts)]. anchor build results in

developer@7c961325b3bd:~/solana/example/programs/example/src$ anchor build
BPF SDK: /home/developer/.local/share/solana/install/releases/1.9.1/solana-release/bin/sdk/bpf
cargo-build-bpf child: rustup toolchain list -v
cargo-build-bpf child: cargo +bpf build --target bpfel-unknown-unknown --release
   Compiling example v0.1.0 (/home/developer/solana/example/programs/example)
error[E0425]: cannot find value `rent` in this scope
  --> programs/example/src/lib.rs:18:10
   |
18 | #[derive(Accounts)]
   |          ^^^^^^^^ not found in this scope
   |
   = 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 E0425`.
error: could not compile `example` due to previous error

I'f I remove the account with the mint:: constraint, this example will still not work. In order to get it compiled I also need to remove the init constraint on the token account (but not the associated_token::). There, I can remove the init constraint, but the mint:: constraint requires the init constraint, so removing it there is not possible.

[fanatid]

You need add rent: Sysvar<'info, Rent>, to MintRequest. Related with #1330.

[EP-u-NW]

Thanks for the very fast answer, that fixed it! Unfortunately, the docs didn't mention that 😅

[fanatid]

Yeah, unfortunately. But you can help by submitting pull request for #1330 😉