Warning: SPDX license identifier not provided in source file

Question

I created a new solidity contract. The contract is up and running but giving me this warning.

Warning: SPDX license identifier not provided in source file. Before publishing, consider adding a comment containing "SPDX-License-Identifier: <SPDX-License>" to each source file. Use "SPDX-License-Identifier: UNLICENSED" for non-open-source code. Please see https://spdx.org for more information.

There are no errors while compilation.

The Compiler version I am using in https://remix.ethereum.org/ is v0.7.5+commit.eb77ed08 Language: Solidity EVM VERSION: compiler default

Whenever I press compile it gives me the warning but there is no problem while deploying.

My code snippet:

pragma solidity ^0.7.5;
contract TestContract {
// Some logic
}

Answer 1

From Solidity ^0.6.8 SPDX license is introduced. So you need to use SPDX-License-Identifier in the code.

Have a look at this: https://forum.openzeppelin.com/t/solidity-0-6-8-introduces-spdx-license-identifiers/2859

For example in your code you need to use license identifier like

// SPDX-License-Identifier: MIT
pragma solidity ^0.7.5;
contract TestContract {
// Some logic
}

You need to use license according to your project. Some other licenses are:

// SPDX-License-Identifier: GPL-3.0-or-later

You can find list of licenses here: https://spdx.org/licenses/