GHC 8.2.2 allows bang patterns in let binding without -XBangPatterns

gistfile1.txt

$ $HOME/.stack/programs/x86_64-linux/ghc-nopie-8.0.2/bin/runghc Main.hs

Main.hs:8:22: error:
    Illegal bang-pattern (use BangPatterns):
    ! x
$ $HOME/.stack/programs/x86_64-linux/ghc-nopie-8.2.2/bin/runghc Main.hs
Compiles
$ $HOME/.stack/programs/x86_64-linux/ghc-nopie-8.2.1/bin/runghc Main.hs
Compiles

Main.hs

--{-# LANGUAGE BangPatterns #-}
module Main where

main :: IO ()
main = putStrLn "Compiles"

letBangPattern :: Int
letBangPattern = let !x = 1 + 2 in x