Missing parentheses for ((let) of []);

[fisker]

Prettier 2.2.1
Playground link

--parser babel

Input:

for ((let) of []);

Output:

for (let of []);

Second Output:

SyntaxError: Unexpected token, expected ";" (1:13)
> 1 | for (let of []);
    |             ^
  2 | 

The parens are also needed in for ((let) of []); and for ((let.foo.bar) of []);.

See https://tc39.es/ecma262/#sec-for-in-and-for-of-statements

Originally posted by @thorn0 in #10777 (comment)

[sosukesuzuki]

summary

according to spec

for in:

for (expression1 in expression2) {}

If expressin1 starts with let[, it should be wrapped by parens.

for of:

for (expression1 of expression2) {}

If expression1 starts with let or async of, it should be wrapped by parens.

for await of:

for await (expression1 of expression2) {}

If expression1 starts with let, it should be wrapped by parens.