Passing -fno-code disables reporting of some warnings

Here is how to reproduce the issue with GHC 8.2.2:

$ cat Main.hs
module Main (main) where

main =
  case (1+1) :: Int of
    1 -> return ()


$ ghc -Wall -Werror -fno-code Main.hs
[1 of 1] Compiling Main             ( Main.hs, nothing )

Main.hs:3:1: warning: [-Wmissing-signatures]
    Top-level binding with no type signature: main :: IO ()
  |
3 | main =
  | ^^^^

<no location info>: error: 
Failing due to -Werror.


$ ghc -Wall -Werror Main.hs
[1 of 1] Compiling Main             ( Main.hs, Main.o )

Main.hs:3:1: warning: [-Wmissing-signatures]
    Top-level binding with no type signature: main :: IO ()
  |
3 | main =
  | ^^^^

Main.hs:4:3: warning: [-Wincomplete-patterns]
    Pattern match(es) are non-exhaustive
    In a case alternative:
        Patterns not matched: p where p is not one of {1}
  |
4 |   case (1+1) :: Int of
  |   ^^^^^^^^^^^^^^^^^^^^...

<no location info>: error: 
Failing due to -Werror.

Note that missing-signature is reported both times, but the incomplete-patterns is not reported with -fno-code.

Trac metadata

Trac field	Value
Version	8.2.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import labels

See #10600 (closed) . I still don't know why the pattern match checking happens in the desugarer but perhaps this is fixed?

closed

Indeed, this is a duplicate of #10600 (closed), as this emits the warning with GHC 8.4.1:

$ /opt/ghc/8.4.1/bin/ghci -Wall -fno-code Bug.hsGHCi, version 8.4.1: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
[1 of 1] Compiling Main             ( Bug.hs, nothing )

Bug.hs:3:1: warning: [-Wmissing-signatures]
    Top-level binding with no type signature: main :: IO ()
  |
3 | main =
  | ^^^^

Bug.hs:4:3: warning: [-Wincomplete-patterns]
    Pattern match(es) are non-exhaustive
    In a case alternative:
        Patterns not matched: p where p is not one of {1}
  |
4 |   case (1+1) :: Int of
  |   ^^^^^^^^^^^^^^^^^^^^...

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedDuplicate
Related	- → #10600 (closed)

added Pnormal label