#15468: add -Wname-shadowing and -Wunused-pattern-binds to the default warnings for ghci -------------------------------------+------------------------------------- Reporter: George | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: 8.8.1 Component: GHCi | Version: 8.4.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by George): * status: closed => new * resolution: invalid => * type: bug => feature request Old description:
In ghc 8.4.3
Without -fbreak-on-exception you get a good error message:
{{{ ghci -ignore-dot-ghci GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help Prelude> let 2 + 2 = 5 Prelude> 2 + 2 5 Prelude> 3 + 3 *** Exception: <interactive>:1:5-13: Non-exhaustive patterns in function + }}}
With -fbreak-on-exception there is no info about the exception:
{{{ ghci -ignore-dot-ghci -fbreak-on-exception GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help Prelude> let 2 + 2 = 5 Prelude> 2 + 2 5 Prelude> 3 + 3 Stopped in <exception thrown>, <unknown> _exception :: e = _ [<unknown>] [<unknown>] Prelude> }}}
In addition, contrary to the documentation, it doesn't seem possible to get ghci to print out the value of the exception
{{{ <unknown>] [<unknown>] Prelude> :print _exception _exception = (_t1::e) [<unknown>] [<unknown>] Prelude> :info _exception _exception :: e -- Defined in ‘interactive:Ghci3’ [<unknown>] [<unknown>] Prelude> }}}
Finally the fact that you get no warning about
{{{ let 2 + 2 = 5 }}}
or for {{{ 2 = 3 }}}
makes me think I should file an ER to add the following to the default warnings for ghci
{{{ ghci -ignore-dot-ghci -Wname-shadowing -Wunused-pattern-binds GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help Prelude> let 2 + 2 = 5
<interactive>:1:7: warning: [-Wname-shadowing] This binding for ‘+’ shadows the existing binding imported from ‘Prelude’ (and originally defined in ‘GHC.Num’) Prelude> 2 = 3
<interactive>:2:1: warning: [-Wunused-pattern-binds] This pattern-binding binds no variables: 2 = 3 Prelude> }}}
I noticed the second and when googling to see if it had been reported I came across the following which documented the first: https://code.likeagirl.io/2-2-5-and-why-compiler-warnings-are-good- eaadef327146
New description: In ghc 8.4.3 {{{ ghci -ignore-dot-ghci GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help Prelude> let 2 + 2 = 5 Prelude> 2 + 2 5 }}} Users get no warning about the preceding or or for {{{ 2 = 3 }}} thus suggest that -Wname-shadowing and -Wunused-pattern-binds be added to the default warnings for ghci {{{ ghci -ignore-dot-ghci -Wname-shadowing -Wunused-pattern-binds GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help Prelude> let 2 + 2 = 5 <interactive>:1:7: warning: [-Wname-shadowing] This binding for ‘+’ shadows the existing binding imported from ‘Prelude’ (and originally defined in ‘GHC.Num’) Prelude> 2 = 3 <interactive>:2:1: warning: [-Wunused-pattern-binds] This pattern-binding binds no variables: 2 = 3 Prelude> }}} I noticed the second and when googling to see if it had been reported I came across the following which documented the first: https://code.likeagirl.io/2-2-5-and-why-compiler-warnings-are-good- eaadef327146 -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15468#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler