GHC 9.6 has less ticks about servant HOT 4 CLOSED

Let's simply deactivate -Wunticked-promoted-constructors for all GHC versions?

from servant.

Let's simply deactivate -Wunticked-promoted-constructors for all GHC versions?

I don't think this works. The issue is not caused by warnings, but it is caused by types in error messages not having the tick as they previously had. To verify this, I added -Wunticked-promoted-constructors to the test-suite of servant-server, and reran the doctest. I still get the failures. I suspect I'd be another flag we'd need to set for older GHCs, one about formatting errors. And I am not sure that exists, since the change of heart on unticked promoted constructors might not have been anticipated such that it'd be available in all the GHC versions we run the doctests for.

Solutions I can think of:

• Only run doctests on GHC <9.6: This would mean keeping the existing ticks in the code
• Only run doctests on GHC >=9.6: This would mean adapting the code to pass the current failing tests, e.g. replacing Verb 'GET with Verb GET.
• Duplicating the test:

  -- | This instance prevents from accidentally using '->' instead of ':>'      
  --                                                                            
  #if __GLASGOW_HASKELL__ >= 906                                                
  -- >>> serve (Proxy :: Proxy (Capture "foo" Int -> Get '[JSON] Int)) (error "...")
  -- ...                                                                        
  -- ...No instance HasServer (a -> b).                                         
  -- ...Maybe you have used '->' instead of ':>' between                        
  -- ...Capture' '[] "foo" Int                                                  
  -- ...and                                                                     
  -- ...Verb GET 200 [JSON] Int                                                 
  -- ...                                                                        
  #else                                                                         
  -- >>> serve (Proxy :: Proxy (Capture "foo" Int -> Get '[JSON] Int)) (error "...")
  -- ...                                                                        
  -- ...No instance HasServer (a -> b).                                         
  -- ...Maybe you have used '->' instead of ':>' between                        
  -- ...Capture' '[] "foo" Int                                                  
  -- ...and                                                                     
  -- ...Verb 'GET 200 '[JSON] Int                                               
  -- ...                                                                        
  #endif
  

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We could also add -fprint-redundant-promotion-ticks to have GHC print it in the old style.

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@voidus Thank you! I have added the flag in #1680 . I would appreciate a review if you have time.

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