Matthew Pickering pushed to branch wip/mp/ghc-9.10.1-determinism at Glasgow Haskell Compiler / GHC

Commits:

• 06ea36f3
  by Matthew Pickering at 2026-02-02T17:28:42+00:00

  determinism: Use a stable sort in WithHsDocIdentifiers binary instance
  
  `WithHsDocIdentifiers` is defined as
  
  ```
   71 data WithHsDocIdentifiers a pass = WithHsDocIdentifiers
   72   { hsDocString      :: !a
   73   , hsDocIdentifiers :: ![Located (IdP pass)]
   74   }
  ```
  
  This list of names is populated from `rnHsDocIdentifiers`, which calls
  `lookupGRE`, which calls `lookupOccEnv_AllNameSpaces`, which calls
  `nonDetEltsUFM` and returns the results in an order depending on
  uniques.
  
  Sorting the list with a stable sort before returning the interface makes
  the output deterministic and follows the approach taken by other fields
  in `Docs`.
  
  Fixes #26858
  

1 changed file:

• compiler/GHC/Hs/Doc.hs

Changes:

 import GHC.Hs.Extension

 import GHC.Types.Unique.Map

 import Data.List (sortBy)

+import Data.Function

 import GHC.Hs.DocString

 instance Binary a => Binary (WithHsDocIdentifiers a GhcRn) where

   put_ bh (WithHsDocIdentifiers s ids) = do

     put_ bh s

-    put_ bh $ BinLocated <$> ids

+    put_ bh $ BinLocated <$> (sortBy  (stableNameCmp `on` getName) ids)

   get bh =

     liftA2 WithHsDocIdentifiers (get bh) (fmap unBinLocated <$> get bh)