Commit abd4a4c1 authored by Ryan Scott's avatar Ryan Scott

Make note of #12881 in 8.0.2 release notes

Summary: Resolves #12881.

Test Plan: Read it, commit it, merge it, ship it

Reviewers: hvr, simonpj, austin, bgamari

Reviewed By: simonpj

Subscribers: simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D2760

GHC Trac Issues: #12881
parent 3aa93689
......@@ -50,6 +50,21 @@ Language
type-checked in GHC 8.0.1 are now rejected by GHC 8.0.2. See
:ghc-ticket:`12784` for details.
- Some programs which combine default type class method implementations and
overlapping instances may now fail to type-check. Here is an example: ::
class Foo a where
foo :: a -> [a]
foo _ = []
instance Foo a
instance Foo Int
The problem is that the overlapping ``Foo Int`` instance is not explicitly
marked as overlapping. To fix this, simply add an ``OVERLAPPING`` pragma: ::
instance {-# OVERLAPPING #-} Foo Int
Compiler
~~~~~~~~
......
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