[BUG]: quick start example fails to compile

[benma]

Following https://docs.nexus.xyz/zkvm/sdk-quick-start

with the given host and guest example programs:

#![cfg_attr(target_arch = "riscv32", no_std, no_main)]
 
use nexus_rt::{println, read_private_input, write_output};
 
#[nexus_rt::main]
fn main() {
    let input = read_private_input::<(u32, u32)>();
 
    let mut z: i32 = -1;
    if let Ok((x, y)) = input {
        println!("Read private input: ({}, {})", x, y);
 
        z = (x * y) as i32;
    } else {
        println!("No private input provided...");
    }
 
    write_output::<i32>(&z)
}

use nexus_sdk::{
    compile::CompileOpts,
    nova::seq::{Generate, Nova, PP},
    Local, Prover, Verifiable,
};
 
type Input = (u32, u32);
type Output = i32;
 
const PACKAGE: &str = "guest";
 
fn main() {
    println!("Setting up Nova public parameters...");
    let pp: PP = PP::generate().expect("failed to generate parameters");
 
    let mut opts = CompileOpts::new(PACKAGE);
    opts.set_memlimit(8); // use an 8mb memory
 
    println!("Compiling guest program...");
    let prover: Nova<Local> = Nova::compile(&opts).expect("failed to compile guest program");
 
    let input: Input = (3, 5);
 
    print!("Proving execution of vm...");
    let proof = prover
        .prove_with_input::<Input>(&pp, &input)
        .expect("failed to prove program");
 
    println!(
        " output is {}!",
        proof
            .output::<Output>()
            .expect("failed to deserialize output")
    );
 
    println!(">>>>> Logging\n{}<<<<<", proof.logs().join("\n"));
 
    print!("Verifying execution...");
    proof.verify(&pp).expect("failed to verify proof");
 
    println!("  Succeeded!");
}

Then running cargo run -r fails with

cargo run -r
warning: Patch `ark-pallas v0.4.0 (https://github.com/arkworks-rs/curves/?rev=8c0256a#8c0256ac)` was not used in the crate graph.
Patch `ark-test-curves v0.4.2 (https://github.com/arkworks-rs/algebra/?rev=2a80c54#2a80c546)` was not used in the crate graph.
Patch `ark-vesta v0.4.0 (https://github.com/arkworks-rs/curves/?rev=8c0256a#8c0256ac)` was not used in the crate graph.
Check that the patched package version and available features are compatible
with the dependency requirements. If the patch has a different version from
what is locked in the Cargo.lock file, run `cargo update` to use the new
version. This may also occur with an optional dependency that is not enabled.
    Finished `release` profile [optimized] target(s) in 0.29s
     Running `target/release/nexus-host`
Setting up Nova public parameters...

Compiling guest program...
warning: Patch `ark-pallas v0.4.0 (https://github.com/arkworks-rs/curves/?rev=8c0256a#8c0256ac)` was not used in the crate graph.
Patch `ark-test-curves v0.4.2 (https://github.com/arkworks-rs/algebra/?rev=2a80c54#2a80c546)` was not used in the crate graph.
Patch `ark-vesta v0.4.0 (https://github.com/arkworks-rs/curves/?rev=8c0256a#8c0256ac)` was not used in the crate graph.
Check that the patched package version and available features are compatible
with the dependency requirements. If the patch has a different version from
what is locked in the Cargo.lock file, run `cargo update` to use the new
version. This may also occur with an optional dependency that is not enabled.
   Compiling postcard v1.0.9
error[E0432]: unresolved import `alloc::sync`
   --> /home/user/.cargo/registry/src/index.crates.io-6f17d22bba15001f/postcard-1.0.9/src/max_size.rs:5:33
    |
5   | use alloc::{boxed::Box, rc::Rc, sync::Arc};
    |                                 ^^^^ could not find `sync` in `alloc`
    |
note: found an item that was configured out
   --> /home/user/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/lib.rs:254:9
    |
254 | pub mod sync;
    |         ^^^^

For more information about this error, try `rustc --explain E0432`.
error: could not compile `postcard` (lib) due to 1 previous error
thread 'main' panicked at src/main.rs:20:52:
failed to compile guest program: BuildError(CompilerError)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Project Information

No response

Reproduction Steps

See above

What is expected?

Output like documented:

Setting up Nova public parameters...
Proving execution of vm... output is 15!
>>>>> Logging
Read private input: (3, 5)
<<<<<
Verifying execution...  Succeeded!

What is actually happening?

See above

System Information

No response

Any additional comments?

No response

[sjudson]

Thanks for the report. This coincides with a new release to postcard, and we're investigating the root cause and working on a fix.

[benma]

Thanks, but how do I know fix my existing nexus-host example program from the quickstart docs?

[sjudson]

Opened upstream issue: jamesmunns/postcard#167

[sjudson]

@benma a new patch release with a fix (v0.2.2) just went out. The easiest way to fix is likely to restart the quickstart (including reinstalling cargo-nexus) using the updated version.