for (let a = b => b in c; ;);

[mdjermanovic]

The following code:

for (let a = b => b in c; ;);

produces a SyntaxError in Node/Chrome/Firefox, as it is viewed as an invalid for-in loop.

However, it's a valid ForStatement in Acorn, so there is a difference. I'm not sure who is right.

[pvdz]

This example is a syntax error because the binding cannot have an initialization. Web compat / AnnexB does allow for inits for var in this case. But that rule does not apply to let.

https://tc39.es/ecma262/#sec-iteration-statements
(Note that all cases starting with for (let require a LeftHandSideExpression production, which does not include assignments)
https://tc39.es/ecma262/#sec-initializers-in-forin-statement-heads

[marijnh]

Should be solved by attached patch.