Solidity ^0.6.0 Truffle Compile Error: Cannot read property ... of undefined

Question

I initalised a new truffle project by using truffle init.

I changed the solc version to ^0.6.0 in the truffle-config.js file.

I ran truffle compile and got this error:

TypeError: Error parsing C:/init-truffle/contracts/Migrations.sol: Cannot read property 'addFunction' of undefined
    at runWithReadCallback (C:\Users\Lino\AppData\Roaming\npm\node_modules\truffle\build\webpack:\~\solc\wrapper.js:37:1)
    at compileStandard (C:\Users\Lino\AppData\Roaming\npm\node_modules\truffle\build\webpack:\~\solc\wrapper.js:78:1)
    at Object.compileStandardWrapper (C:\Users\Lino\AppData\Roaming\npm\node_modules\truffle\build\webpack:\~\solc\wrapper.js:85:1)
    at Object.parseImports (C:\Users\Lino\AppData\Roaming\npm\node_modules\truffle\build\webpack:\packages\truffle-compile\parser.js:47:1)
    at Object.getImports (C:\Users\Lino\AppData\Roaming\npm\node_modules\truffle\build\webpack:\packages\truffle-compile\profiler.js:374:1)
    at Promise.all.then.results (C:\Users\Lino\AppData\Roaming\npm\node_modules\truffle\build\webpack:\packages\truffle-compile\profiler.js:346:1)
Truffle v5.0.5 (core: 5.0.5)
Node v10.16.3

Here is the Migration.sol file:

pragma solidity >=0.4.21 <0.7.0;

contract Migrations {
  address public owner;
  uint public last_completed_migration;

  constructor() public {
    owner = msg.sender;
  }

  modifier restricted() {
    if (msg.sender == owner) _;
  }

  function setCompleted(uint completed) public restricted {
    last_completed_migration = completed;
  }
}

Here is the 1_initial_migration.js file:

const Migrations = artifacts.require("Migrations");

module.exports = function(deployer) {
  deployer.deploy(Migrations);
};

Does anyone know what to do? This file compile without any problems with solc version set to ^0.5.0.

Environment:

• Operating System: Windows 10
• Truffle v5.0.5 (core: 5.0.5)
• Node v10.16.3

Thanks

Answer 1

Turn out that Truffle v5 versions earlier than v5.1.5 won't successfully compile ^0.6.0 solidity contracts, because the solc wrapper Truffle used (directly from solc-js) was only compatible with ^0.5.0 contracts.

The solution is to update the truffle package using npm update -g truffle

Thanks to CruzMolina from GitHub !