EmptyCase produces incorrect SrcSpans
If you compile the following program, you'll get a warning for f
with an improperly placed SrcSpan
:
{-# LANGUAGE EmptyCase #-}
{-# LANGUAGE TypeOperators #-}
{-# OPTIONS_GHC -Wincomplete-patterns #-}
module Bug where
import Data.Type.Equality
can'tHappen :: Int :~: Bool
can'tHappen = undefined
f, g :: Bool -> Bool
f True = case can'tHappen of {}
g True = case () of () -> True
$ /opt/ghc/8.4.2/bin/ghci Bug.hs
GHCi, version 8.4.2: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
[1 of 1] Compiling Bug ( Bug.hs, interpreted )
Bug.hs:12:1: warning: [-Wincomplete-patterns]
Pattern match(es) are non-exhaustive
In an equation for ‘f’: Patterns not matched: False
|
12 | f True = case can'tHappen of {}
| ^^^^^^^^^^^^^
Bug.hs:13:1: warning: [-Wincomplete-patterns]
Pattern match(es) are non-exhaustive
In an equation for ‘g’: Patterns not matched: False
|
13 | g True = case () of () -> True
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Ok, one module loaded.
Compare that to the warning for g
, whose SrcSpan
spans the entire clause, as expected.
The bug lies in the parser—patch incoming.
Trac metadata
Trac field | Value |
---|---|
Version | 8.4.2 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Parser) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |