babel/packages/babel-plugin-transform-block-scoping/test/fixtures/general/issue-4363/input.js

function WithoutCurlyBraces() {
  if (true)
    for (let k in kv) {
        function foo() { return this }
        function bar() { return foo.call(this) }
        console.log(this, k) // => undefined
    }
}

function WithCurlyBraces() {
  if (true) {
    for (let k in kv) {
        function foo() { return this }
        function bar() { return foo.call(this) }
        console.log(this, k) // => 777
    }
  }
}