solidity/test/libsolidity/syntaxTests/immutable/function_pointer_reading.sol

contract B {
    uint immutable x;

    constructor(function() internal returns(uint) fp) internal {
        x = fp();
    }
}

contract C is B(C.f) {
    function f() internal returns(uint) { return x + 2; }
}
// ----
// TypeError 7733: (200-201): Immutable variables cannot be read during contract creation time, which means they cannot be read in the constructor or any function or modifier called from it.