BUG: Variable Declarations are shadowed in for and while-loops

[joshuahannan]

Problem

In a function, a variable can be declared in a subscope with the same name as another variable in the function, which shadows the previously declared variable. This shouldn't be allowed.

Steps to Reproduce

1. Copy this contract

pub contract Nodes {
    init() {
        var node = 1

        var i = 1
        // are we supposed to be allowed to use a name that we've already used?
        while i < 10 {

            // which num is used for the assignment?
            var node = 3
            log(node)
            i = i + 1
        }
        log(node)
    }
}

2. Deploy it and see that there are no errors.

Acceptance Criteria

Checker should report an error that the variable with the same name cannot be declared in a subscope.

[turbolent]

This is working as expected: From https://github.com/onflow/cadence/blob/master/docs/language.md#scope:

Every function and block ({ ... }) introduces a new scope for declarations

However, you had reported that the variable introduces by a for-in loop was shadowing, which is not correct. Can you please adjust this issue or create a new one for that problem?