-Wunused-type-patterns warnings have odd SrcSpans
Consider the following program:
{-# LANGUAGE TypeFamilies #-}
{-# OPTIONS_GHC -Wunused-type-patterns #-}
module Bug where
type family F a b c
type instance F Char b Int = ()
$ /opt/ghc/8.6.5/bin/ghci Bug.hs
GHCi, version 8.6.5: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
[1 of 1] Compiling Bug ( Bug.hs, interpreted )
Bug.hs:6:17: warning: [-Wunused-type-patterns]
Defined but not used: type variable ‘b’
|
6 | type instance F Char b Int = ()
| ^^^^^^^^^^
Even though the culprit behind this warning is b
, the associated SrcSpan
points to all of F
's type patterns.
Patch incoming.