Simon Peyton Jones pushed to branch wip/T26258 at Glasgow Haskell Compiler / GHC Commits: 1f9e4f54 by Stephen Morgan at 2025-08-03T15:14:08+10:00 refactor: Modify Data.List.sortOn to use (>) instead of compare. (#26184) This lets a more efficient (>) operation be used if one exists. This is technically a breaking change for malformed Ord instances, where x > y is not equivalent to compare x y == GT. Discussed by the CLC in issue #332: https://github.com/haskell/core-libraries-committee/issues/332 - - - - - 4f6bc9cf by fendor at 2025-08-04T17:50:06-04:00 Revert "base: Expose Backtraces constructor and fields" This reverts commit 17db44c5b32fff82ea988fa4f1a233d1a27bdf57. - - - - - 00ce1eb9 by Simon Peyton Jones at 2025-08-05T10:32:34+01:00 In TcSShortCut, typechecker plugins should get empty Givens Solving in TcShortCut mode means /ignoring the Givens/. So we should not pass them to typechecker plugins! Fixes #26258. This is a fixup to the earlier MR: commit 1bd12371feacc52394a0e660ef9349f9e8ee1c06 Author: Simon Peyton Jones <simon.peytonjones@gmail.com> Date: Mon Jul 21 10:04:49 2025 +0100 Improve treatment of SPECIALISE pragmas -- again! - - - - - 11 changed files: - compiler/GHC/Tc/Solver/Dict.hs - compiler/GHC/Tc/Solver/Monad.hs - compiler/GHC/Tc/Solver/Solve.hs - libraries/base/changelog.md - libraries/base/src/Control/Exception/Backtrace.hs - libraries/base/src/Data/List/NonEmpty.hs - libraries/ghc-internal/src/GHC/Internal/Data/OldList.hs - testsuite/tests/interface-stability/base-exports.stdout - testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs - testsuite/tests/interface-stability/base-exports.stdout-mingw32 - testsuite/tests/interface-stability/base-exports.stdout-ws-32 Changes: ===================================== compiler/GHC/Tc/Solver/Dict.hs ===================================== @@ -496,11 +496,15 @@ We could use the Eq [a] superclass of the Ord [a], or we could use the top-level instance `Eq a => Eq [a]`. But if we did the latter we'd be stuck with an insoluble constraint (Eq a). -So the ShortCutSolving rule is this: +----------------------------------- +So the ShortCutSolving plan is this: If we could solve a constraint from a local Given, - try first to /completely/ solve the constraint using only top-level instances. + try first to /completely/ solve the constraint + using only top-level instances, + /without/ using any local Givens. - If that succeeds, use it - If not, use the local Given +----------------------------------- An example that succeeds: @@ -555,7 +559,7 @@ The moving parts are relatively simple: - `matchLocalInst`, which would otherwise consult Given quantified constraints - `GHC.Tc.Solver.Instance.Class.matchInstEnv`: when short-cut solving, don't pick overlappable top-level instances - + - `GHC.Tc.Solver.Solve.runTcPluginsWanted`: don't pass any Givens to the plugin Some wrinkles: ===================================== compiler/GHC/Tc/Solver/Monad.hs ===================================== @@ -897,14 +897,19 @@ for it, so TcS carries a mutable location where the binding can be added. This is initialised from the innermost implication constraint. -} --- | See Note [TcSMode] -data TcSMode +data TcSMode -- | See Note [TcSMode], where each constructor is documented = TcSVanilla -- ^ Normal constraint solving | TcSPMCheck -- ^ Used when doing patterm match overlap checks | TcSEarlyAbort -- ^ Abort early on insoluble constraints | TcSShortCut -- ^ Fully solve all constraints, without using local Givens deriving (Eq) +instance Outputable TcSMode where + ppr TcSVanilla = text "TcSVanilla" + ppr TcSPMCheck = text "TcSPMCheck" + ppr TcSEarlyAbort = text "TcSEarlyAbort" + ppr TcSShortCut = text "TcSShortcut" + {- Note [TcSMode] ~~~~~~~~~~~~~~~~~ The constraint solver can operate in different modes: ===================================== compiler/GHC/Tc/Solver/Solve.hs ===================================== @@ -1011,9 +1011,17 @@ solveSimpleGivens givens solveSimpleWanteds :: Cts -> TcS Cts -- The result is not necessarily zonked solveSimpleWanteds simples - = do { traceTcS "solveSimpleWanteds {" (ppr simples) + = do { mode <- getTcSMode ; dflags <- getDynFlags + ; inerts <- getInertSet + + ; traceTcS "solveSimpleWanteds {" $ + vcat [ text "Mode:" <+> ppr mode + , text "Inerts:" <+> ppr inerts + , text "Wanteds to solve:" <+> ppr simples ] + ; (n,wc) <- go 1 (solverIterations dflags) simples + ; traceTcS "solveSimpleWanteds end }" $ vcat [ text "iterations =" <+> ppr n , text "residual =" <+> ppr wc ] @@ -1663,17 +1671,26 @@ runTcPluginsGiven -- 'solveSimpleWanteds' should feed the updated wanteds back into the -- main solver. runTcPluginsWanted :: Cts -> TcS (Bool, Cts) -runTcPluginsWanted simples1 - | isEmptyBag simples1 - = return (False, simples1) +runTcPluginsWanted wanted + | isEmptyBag wanted + = return (False, wanted) | otherwise = do { solvers <- getTcPluginSolvers - ; if null solvers then return (False, simples1) else + ; if null solvers then return (False, wanted) else - do { given <- getInertGivens - ; wanted <- TcS.zonkSimples simples1 -- Plugin requires zonked inputs + do { -- Find the set of Givens to give to the plugin. + -- If TcSMode = TcSShortCut, we are solving with + -- no Givens so don't return any (#26258)! + -- See Note [Shortcut solving] in GHC.Tc.Solver.Dict + mode <- getTcSMode + ; given <- case mode of + TcSShortCut -> return [] + _ -> getInertGivens - ; traceTcS "Running plugins (" (vcat [ text "Given:" <+> ppr given + -- Plugin requires zonked input wanteds + ; zonked_wanted <- TcS.zonkSimples wanted + + ; traceTcS "Running plugins {" (vcat [ text "Given:" <+> ppr given , text "Wanted:" <+> ppr wanted ]) ; p <- runTcPluginSolvers solvers (given, bagToList wanted) ; let (_, solved_wanted) = pluginSolvedCts p @@ -1684,9 +1701,6 @@ runTcPluginsWanted simples1 listToBag unsolved_wanted `andCts` listToBag insols --- SLPJ: I'm deeply suspicious of this --- ; updInertCans (removeInertCts $ solved_givens) - ; mapM_ setEv solved_wanted ; traceTcS "Finished plugins }" (ppr new_wanted) ===================================== libraries/base/changelog.md ===================================== @@ -3,6 +3,7 @@ ## 4.23.0.0 *TBA* * Add `Data.List.NonEmpty.mapMaybe`. ([CLC proposal #337](https://github.com/haskell/core-libraries-committee/issues/337)) * Fix issues with toRational for types capable to represent infinite and not-a-number values ([CLC proposal #338](https://github.com/haskell/core-libraries-committee/issues/338)) + * Modify the implementation of `Data.List.sortOn` to use `(>)` instead of `compare`. ([CLC proposal #332](https://github.com/haskell/core-libraries-committee/issues/332)) ## 4.22.0.0 *TBA* * Shipped with GHC 9.14.1 @@ -29,7 +30,6 @@ * `GHC.TypeNats.Internal` * `GHC.ExecutionStack.Internal`. * Deprecate `GHC.JS.Prim.Internal.Build`, as per [CLC #329](https://github.com/haskell/core-libraries-committee/issues/329) - * Expose constructor and field of `Backtraces` from `Control.Exception.Backtrace`, as per [CLC #199](https://github.com/haskell/core-libraries-committee/issues/199#issuecomment-...) * Fix incorrect results of `integerPowMod` when the base is 0 and the exponent is negative, and `integerRecipMod` when the modulus is zero ([#26017](https://gitlab.haskell.org/ghc/ghc/-/issues/26017)). * Fix the rewrite rule for `scanl'` not being strict in the first element of the output list ([#26143](https://gitlab.haskell.org/ghc/ghc/-/issues/26143)). ===================================== libraries/base/src/Control/Exception/Backtrace.hs ===================================== @@ -51,7 +51,7 @@ module Control.Exception.Backtrace , getBacktraceMechanismState , setBacktraceMechanismState -- * Collecting backtraces - , Backtraces(..) + , Backtraces , displayBacktraces , collectBacktraces ) where ===================================== libraries/base/src/Data/List/NonEmpty.hs ===================================== @@ -268,6 +268,9 @@ sort = lift List.sort -- >>> (sortBy . comparing) fst $ (3, 1) :| [(2, 2), (1, 3)] -- (1,3) :| [(2,2),(3,1)] -- +-- However, 'sortOn' may still be faster for instances with a more efficient +-- implementation of '(>)' than 'compare'. +-- -- 'sortWith' is an alias for `sortBy . comparing`. -- -- @since 4.20.0.0 ===================================== libraries/ghc-internal/src/GHC/Internal/Data/OldList.hs ===================================== @@ -216,7 +216,6 @@ module GHC.Internal.Data.OldList import GHC.Internal.Data.Maybe import GHC.Internal.Data.Bits ( (.&.) ) import GHC.Internal.Unicode ( isSpace ) -import GHC.Internal.Data.Ord ( comparing ) import GHC.Internal.Data.Tuple ( fst, snd ) import GHC.Internal.Num @@ -1862,10 +1861,13 @@ rqpart cmp x (y:ys) rle rgt r = -- >>> (sortBy . comparing) fst [(3, 1), (2, 2), (1, 3)] -- [(1,3),(2,2),(3,1)] -- +-- However, 'sortOn' may still be faster for instances with a more efficient +-- implementation of '(>)' than 'compare'. +-- -- @since base-4.8.0.0 sortOn :: Ord b => (a -> b) -> [a] -> [a] sortOn f = - map snd . sortBy (comparing fst) . map (\x -> let y = f x in y `seq` (y, x)) + map snd . actualSort (\x y -> fst x > fst y) . map (\x -> let y = f x in y `seq` (y, x)) -- | Construct a list from a single element. -- ===================================== testsuite/tests/interface-stability/base-exports.stdout ===================================== @@ -323,7 +323,7 @@ module Control.Exception.Backtrace where type BacktraceMechanism :: * data BacktraceMechanism = CostCentreBacktrace | HasCallStackBacktrace | ExecutionBacktrace | IPEBacktrace type Backtraces :: * - data Backtraces = Backtraces {btrCostCentre :: GHC.Internal.Maybe.Maybe (GHC.Internal.Ptr.Ptr GHC.Internal.Stack.CCS.CostCentreStack), btrHasCallStack :: GHC.Internal.Maybe.Maybe GHC.Internal.Stack.Types.CallStack, btrExecutionStack :: GHC.Internal.Maybe.Maybe [GHC.Internal.ExecutionStack.Internal.Location], btrIpe :: GHC.Internal.Maybe.Maybe [GHC.Internal.Stack.CloneStack.StackEntry]} + data Backtraces = ... collectBacktraces :: (?callStack::GHC.Internal.Stack.Types.CallStack) => GHC.Internal.Types.IO Backtraces displayBacktraces :: Backtraces -> GHC.Internal.Base.String getBacktraceMechanismState :: BacktraceMechanism -> GHC.Internal.Types.IO GHC.Internal.Types.Bool ===================================== testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs ===================================== @@ -323,7 +323,7 @@ module Control.Exception.Backtrace where type BacktraceMechanism :: * data BacktraceMechanism = CostCentreBacktrace | HasCallStackBacktrace | ExecutionBacktrace | IPEBacktrace type Backtraces :: * - data Backtraces = Backtraces {btrCostCentre :: GHC.Internal.Maybe.Maybe (GHC.Internal.Ptr.Ptr GHC.Internal.Stack.CCS.CostCentreStack), btrHasCallStack :: GHC.Internal.Maybe.Maybe GHC.Internal.Stack.Types.CallStack, btrExecutionStack :: GHC.Internal.Maybe.Maybe [GHC.Internal.ExecutionStack.Internal.Location], btrIpe :: GHC.Internal.Maybe.Maybe [GHC.Internal.Stack.CloneStack.StackEntry]} + data Backtraces = ... collectBacktraces :: (?callStack::GHC.Internal.Stack.Types.CallStack) => GHC.Internal.Types.IO Backtraces displayBacktraces :: Backtraces -> GHC.Internal.Base.String getBacktraceMechanismState :: BacktraceMechanism -> GHC.Internal.Types.IO GHC.Internal.Types.Bool ===================================== testsuite/tests/interface-stability/base-exports.stdout-mingw32 ===================================== @@ -323,7 +323,7 @@ module Control.Exception.Backtrace where type BacktraceMechanism :: * data BacktraceMechanism = CostCentreBacktrace | HasCallStackBacktrace | ExecutionBacktrace | IPEBacktrace type Backtraces :: * - data Backtraces = Backtraces {btrCostCentre :: GHC.Internal.Maybe.Maybe (GHC.Internal.Ptr.Ptr GHC.Internal.Stack.CCS.CostCentreStack), btrHasCallStack :: GHC.Internal.Maybe.Maybe GHC.Internal.Stack.Types.CallStack, btrExecutionStack :: GHC.Internal.Maybe.Maybe [GHC.Internal.ExecutionStack.Internal.Location], btrIpe :: GHC.Internal.Maybe.Maybe [GHC.Internal.Stack.CloneStack.StackEntry]} + data Backtraces = ... collectBacktraces :: (?callStack::GHC.Internal.Stack.Types.CallStack) => GHC.Internal.Types.IO Backtraces displayBacktraces :: Backtraces -> GHC.Internal.Base.String getBacktraceMechanismState :: BacktraceMechanism -> GHC.Internal.Types.IO GHC.Internal.Types.Bool ===================================== testsuite/tests/interface-stability/base-exports.stdout-ws-32 ===================================== @@ -323,7 +323,7 @@ module Control.Exception.Backtrace where type BacktraceMechanism :: * data BacktraceMechanism = CostCentreBacktrace | HasCallStackBacktrace | ExecutionBacktrace | IPEBacktrace type Backtraces :: * - data Backtraces = Backtraces {btrCostCentre :: GHC.Internal.Maybe.Maybe (GHC.Internal.Ptr.Ptr GHC.Internal.Stack.CCS.CostCentreStack), btrHasCallStack :: GHC.Internal.Maybe.Maybe GHC.Internal.Stack.Types.CallStack, btrExecutionStack :: GHC.Internal.Maybe.Maybe [GHC.Internal.ExecutionStack.Internal.Location], btrIpe :: GHC.Internal.Maybe.Maybe [GHC.Internal.Stack.CloneStack.StackEntry]} + data Backtraces = ... collectBacktraces :: (?callStack::GHC.Internal.Stack.Types.CallStack) => GHC.Internal.Types.IO Backtraces displayBacktraces :: Backtraces -> GHC.Internal.Base.String getBacktraceMechanismState :: BacktraceMechanism -> GHC.Internal.Types.IO GHC.Internal.Types.Bool View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/e087f4adcb22a3b83cd64276c74f252... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/e087f4adcb22a3b83cd64276c74f252... 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