Bug Report

Input Code

packages/babel-generator/test/fixtures/types/ArrowFunctionExpression2/input.js:

const pair = <T>(a: T): (T => T[]) => b => [a, b]

packages/babel-generator/test/fixtures/types/ArrowFunctionExpression2/options.json:

{ "plugins": ["flow"] }

Expected behavior/code
The output should be the same as the input, with the parentheses around (T => T[]).

Current Behavior
Output code is:

const pair = <T>(a: T): (T) => T[] => b => [a, b];

The parentheses have moved from (T => T[]) to (T) => T[].
Flow now gives a parse error on the output, where it worked for the original.

Environment

• Babel version(s): master
• Node/npm version: Node 10/npm 6
• OS: Linux Mint 18.1
• Monorepo: yes
• How you are using Babel: env TEST_ONLY=babel-generator make test