GHC HEAD no longer reports inaccessible code

Given this A.hs:

{-# LANGUAGE GADTs #-}
module A where
f :: Bool ~ Int => a -> b
f x = x

I get:

ezyang@sabre:~$ ghc-head --version
The Glorious Glasgow Haskell Compilation System, version 8.1.20161010
ezyang@sabre:~$ ghc-head --make A.hs 
[1 of 1] Compiling A                ( A.hs, A.o )

A.hs:4:1: warning: [-Woverlapping-patterns]
    Pattern match is redundant
    In an equation for ‘f’: f x = ...

In contrast:

ezyang@sabre:~$ ghc-8.0 --make A.hs 
[1 of 1] Compiling A                ( A.hs, A.o )

A.hs:3:6: error:
    • Couldn't match type ‘Bool’ with ‘Int’
      Inaccessible code in
        the type signature for:
          f :: Bool ~ Int => a -> b
    • In the ambiguity check for ‘f’
      To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
      In the type signature:
        f :: Bool ~ Int => a -> b

Is this expected? I'd expect at least a warning!

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	goldfire
Operating system
Architecture