Solidity: Disallow override for non-public state variables.

[ddeclerck]

When a public state variable overrides an external functions, it doesn't seem to check that the overriden function is marked "virtual" (while if we override with a function, then the overriden function MUST be marked "virtual").

The following typechecks without error nor warnings:

contract C1 {
  function f() external pure returns(int) { return 42; }
}

contract C is C1 {
   int override f;
}

It should report something like "Trying to override non-virtual function."

[chriseth]

Note that in the example, C.f is not public, and thus cannot even override anything.

[ekpyron]

The actual solution here is to disallow override for state variables that aren't public, right?

[chriseth]

Sounds like a plan!