How to use anchor-gen to import a program built with another version of anchor?

Question

I'm trying to build a program using anchor v0.25.0 that makes calls to Orca's Whirlpools. But whirlpools are built using anchor v0.20.2 and that raises errors when running anchor build.

I found this question that suggests using anchor-gen which is exactly what I need.

However, there is no usage example of how to use anchor-gen. What I did was add a folder at the root of my Anchor project called generated in which I have a subfolder for each external program I want to integrate. Inside these subfolders, there is a small crate that has anchor-gen v0.3.0 as dependency, the corresponding IDL and a src/lib.rs file that uses the generate_cpi_interface or generate_cpi_crate macro called.

The problem I run into is that when I import struct and functions from the generated whirlpool crate, I have an error saying that it is private.

I import the generated crate like this:

use whirlpools::{self, swap, Swap, TickArray, Whirlpool};

And I run into this error:

cargo-build-bpf child: rustup toolchain list -v
cargo-build-bpf child: cargo +bpf build --target bpfel-unknown-unknown --release
Error: Function _ZN10whirlpools81_$LT$impl$u20$core..default..Default$u20$for$u20$whirlpools..state..TickArray$GT$7default17hc7fbe4eca82a6568E Stack offset of 9944 exceeded max offset of 4096 by 5848 bytes, please minimize large stack variables
   Compiling test v0.1.0 (programs/test)
error[E0603]: struct `Swap` is private
  --> programs/arb-bot/src/instructions/arb_that_shit.rs:6:24
   |
6  | use whirlpools::{self, Swap, TickArray, Whirlpool};
   |                        ^^^^ private struct
   |
note: the struct `Swap` is defined here
  --> programs/whirlpools/src/lib.rs:10:1
   |
10 | / anchor_gen::generate_cpi_interface!(
11 | |     idl_path = "idl.json",
12 | |     zero_copy(TickArray, Tick),
13 | |     packed(TickArray, Tick)
14 | | );
   | |__^
   = note: this error originates in the macro `anchor_gen::generate_cpi_interface` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0603`.
error: could not compile `arb-bot` due to previous error

What causes this error and how can I fix it?

Thanks

Answer 1

The crate needs to be imported like this:

// After
use whirlpools::{
    cpi::{accounts::Swap, swap},
    TickArray, Whirlpool,
};