How to configure multiple solidity compiler versions in foundry?

Question

I have a foundry project with files that have multiple solidity versions(0.7.x and 0.8.x). hardhat can relatively easily be configured to compile all files in the project as follows:

https://hardhat.org/hardhat-runner/docs/advanced/multiple-solidity-versions

Does foundry have built-in support for multiple solidity compiler versions? I came across a hacky way to do this which is non-ideal and I don't want to take this approach.

Answer 1

So it doesn't seem like Foundry allows you to manually configure multiple solc versions however Foundry does automatically detect and configure the required compilers for your project, you'll need to make sure of the following:

• Do not explicitly configure a solidity compiler version i.e. do not set the solc variable in your foundry.toml config.

• Ensure that auto_detect_solc is set to true or leave it unconfigured(since the default value is true).

Here's an example of what your foundry.toml might look like:

# foundry.toml

[profile.default]
auto_detect_solc = true
# Do not include the 'solc' variable

Credit to @jaime for pointing me in the right direction.

Answer 2

In the case that auto_detect_solc = true doesn't work, just set the compiler version for accurate testing.

#foundry.toml
// Specify Version
solc_version = "0.8.22"
//auto_detect_solc = true