Recursive let/const references should error

[JsonFreeman]

The constructs:

let v = v;
const c = c;

should error because they are uses before definition. Indeed IE gives this error.

This also applies to:

for (let v = v; ; ) { }
for (let v in v) { }
for (let v of v) { }

For the latter two in particular, look at section 13.6.4.12 in the ES6 spec:

1. Let oldEnv be the running execution context’s LexicalEnvironment.

2. If TDZnames is not an empty List, then

   a. Assert: TDZnames has no duplicate entries.
   b. Let TDZ be NewDeclarativeEnvironment(oldEnv).
   c. For each string name in TDZnames, do

     i. Let status be TDZ.CreateMutableBinding(name, false).
     ii. Assert: status is never an abrupt completion.
   

   d. Set the running execution context’s LexicalEnvironment to TDZ.

3. Let exprRef be the result of evaluating the production that is expr.

4. Set the running execution context’s LexicalEnvironment to oldEnv.