Mixing `groth16` and `plonk` for the same circuit stalls compilation

[camden-smallwood]

When compiling the same circuit using both the groth16 and plonk protocols, compilation will stall after finishing the first circuit, regardless of order. If I comment out either circuit, compilation finishes successfully, but this requires two separate runs of npx hardhat circom. I am using node.js v16.6.1, running on a mac mini M1 with macOS Ventura 13.0.1. I am using the example Multiplier2 template from the circom tutorial.

Here is my package.json file:

{
  "name": "circom-test",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "circomlib": "^2.0.5",
    "hardhat-circom": "^3.3.2"
  },
  "devDependencies": {
    "@nomicfoundation/hardhat-toolbox": "^2.0.0",
    "hardhat": "^2.12.5"
  }
}

Here is my hardhat.config.ts file:

import { HardhatUserConfig } from "hardhat/config";
import "@nomicfoundation/hardhat-toolbox";
import 'hardhat-circom';

const config: HardhatUserConfig = {
  solidity: {
    compilers: [
      {
        version: '0.6.11',
      },
      {
        version: '0.8.17',
      },
    ],
  },
  circom: {
    inputBasePath: './circuits',
    outputBasePath: './circuits/build',
    ptau: 'powersOfTau28_hez_final_18.ptau',
    circuits: [
      {
        name: 'multiplier2',
        circuit: 'multiplier2.circom',
        input: 'input/multiplier2.json',
      },
      {
        name: 'multiplier2_plonk',
        circuit: 'multiplier2.circom',
        input: 'input/multiplier2.json',
        protocol: 'plonk',
      },
    ]
  }
};

export default config;

Here is my circuits/multiplier2.circom file:

pragma circom 2.0.0;

/*This circuit template checks that c is the multiplication of a and b.*/  

template Multiplier2 () {  

   // Declaration of signals.  
   signal input a;  
   signal input b;  
   signal output c;  

   // Constraints.  
   c <== a * b;  
}

Here is my circuits/input/multiplier2.json file:

{ "a": "3", "b": "11" }

[phated]

This worked in circom-starter when I added it, so I'm not sure what issue you are hitting.

[camden-smallwood]

I just tested the circom-starter repository, and by itself it does indeed work fine. However, if I duplicate the division circuit entry in the hardhat.config.js file and make it use the plonk protocol, it appears to stall just the same as my test project right after printing hardhat-circom:info Written successfully: /Users/camden/Source/circom-starter/circuits/division.sym +0ms.

Here is the modified hardhat.config.js for the circom-starter repository:

require("hardhat-circom");

/**
 * @type import('hardhat/config').HardhatUserConfig
 */
module.exports = {
  solidity: {
    compilers: [
      {
        version: "0.6.11",
      },
      {
        version: "0.8.9",
      },
    ],
  },
  circom: {
    inputBasePath: "./circuits",
    ptau: "https://hermezptau.blob.core.windows.net/ptau/powersOfTau28_hez_final_15.ptau",
    circuits: [
      {
        name: "division",
        // No protocol, so it defaults to groth16
      },
      {
        // duplicate of the division circuit using the plonk protocol
        name: 'division_plonk',
        circuit: 'division.circom',
        input: 'division.json',
        protocol: 'plonk',
      },
      {
        name: "simple-polynomial",
        // Generate PLONK
        protocol: "plonk",
      },
      {
        name: "hash",
        // Explicitly generate groth16
        protocol: "groth16",
      },
    ],
  },
};

[phated]

Okay. Using the same circuit multiple times has never been explicitly supported nor tested, so this is more a feature than a bug. Not sure when I'll be able to look/implement. Thanks for the detailed report.

[camden-smallwood]

Thanks for the response, I updated the title to be more clear of the issue.