July 2018 - ghc-tickets

[GHC] #8657: -fregs-graph still has a limit on spill slots
by GHC 04 Mar '19

04 Mar '19

#8657: -fregs-graph still has a limit on spill slots -----------------------------------+--------------------------------------- Reporter: simonmar | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.8.1 Component: Compiler (NCG) | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time crash Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | -----------------------------------+--------------------------------------- The limit on spill slots was removed for the linear register allocator in 7.8, but not for `-fregs-graph`. SHA-1 fails to compile with `-fregs-graph` in 7.8. Related: #7679 (`-fregs-graph` generates poor code with the new codegen). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8657> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 18

[GHC] #12919: Equality not used for substitution
by GHC 04 Mar '19

04 Mar '19

#12919: Equality not used for substitution -------------------------------------+------------------------------------- Reporter: int-index | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This code {{{ {-# LANGUAGE TypeInType, TypeFamilies, GADTs, ConstraintKinds #-} import Data.Kind data N = Z data V :: N -> Type where VZ :: V Z type family VC (n :: N) :: Type where VC Z = Type type family VF (xs :: V n) (f :: VC n) :: Type where VF VZ f = f data Dict c where Dict :: c => Dict c prop :: xs ~ VZ => Dict (VF xs f ~ f) prop = Dict }}} fails with this error: {{{ Op.hs:20:8: error: • Couldn't match type ‘f’ with ‘VF 'VZ f’ arising from a use of ‘Dict’ ‘f’ is a rigid type variable bound by the type signature for: prop :: forall (xs :: V 'Z) f. xs ~ 'VZ => Dict VF xs f ~ f at Op.hs:19:9 • In the expression: Dict In an equation for ‘prop’: prop = Dict • Relevant bindings include prop :: Dict VF xs f ~ f (bound at Op.hs:20:1) }}} However, if I substitute `xs` with `VZ` (by hand) in the type of `prop`, it compiles. Can be reproduced with GHC 8.0.1 but not HEAD. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12919> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 25

[GHC] #14729: normaliseType is not well-kinded
by GHC 04 Mar '19

04 Mar '19

#14729: normaliseType is not well-kinded -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Suppose we have {{{ Proxy :: forall k. k -> Type type family F a type instance F Int = Bool }}} and we're trying to normalise the target {{{ Proxy (F Int) x }}} Clearly, for this target to be well kinded, we need `x :: F Int`. Currently, the output of `normaliseType` is `Proxy Bool x`, which is just plain wrong. I need to implement logic like in `flatten_args` on [https://github.com/goldfirere/ghc my branch] in `normaliseType` to fix this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14729> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 15

[GHC] #14759: ListSetOps WARNING causes tests to fail
by GHC 04 Mar '19

04 Mar '19

#14759: ListSetOps WARNING causes tests to fail -------------------------------------+------------------------------------- Reporter: ezyang | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Example log: ``` +WARNING: file compiler/utils/ListSetOps.hs, line 58 + [Distribution.Backpack, Distribution.Backpack.FullUnitId, + Distribution.Backpack.ModuleShape, + Distribution.Backpack.PreModuleShape, + Distribution.Backpack.ReadyComponent, + Distribution.CabalSpecVersion, Distribution.Compat.Graph, + Distribution.Compat.Semigroup, Distribution.Compiler, + Distribution.License, Distribution.ModuleName, + Distribution.SPDX.License, Distribution.SPDX.LicenseExceptionId, + Distribution.SPDX.LicenseExpression, Distribution.SPDX.LicenseId, + Distribution.SPDX.LicenseReference, + Distribution.Simple.BuildTarget, Distribution.Simple.Compiler, + Distribution.Simple.Doctest, Distribution.Simple.Haddock, + Distribution.Simple.InstallDirs, Distribution.Simple.PackageIndex, + Distribution.Simple.Program.Find, Distribution.Simple.Program.GHC, + Distribution.Simple.Program.Types, Distribution.Simple.Setup, + Distribution.System, Distribution.Types.AbiDependency, + Distribution.Types.AbiHash, Distribution.Types.Benchmark, + Distribution.Types.BenchmarkInterface, + Distribution.Types.BenchmarkType, Distribution.Types.BuildInfo, + Distribution.Types.BuildType, Distribution.Types.ComponentId, + Distribution.Types.ComponentLocalBuildInfo, + Distribution.Types.ComponentName, + Distribution.Types.ComponentRequestedSpec, + Distribution.Types.CondTree, Distribution.Types.Condition, + Distribution.Types.Dependency, Distribution.Types.ExeDependency, + Distribution.Types.Executable, Distribution.Types.ExecutableScope, + Distribution.Types.ExposedModule, Distribution.Types.ForeignLib, + Distribution.Types.ForeignLibOption, + Distribution.Types.ForeignLibType, + Distribution.Types.GenericPackageDescription, + Distribution.Types.IncludeRenaming, + Distribution.Types.InstalledPackageInfo, + Distribution.Types.LegacyExeDependency, Distribution.Types.Library, + Distribution.Types.LocalBuildInfo, Distribution.Types.Mixin, + Distribution.Types.Module, Distribution.Types.ModuleReexport, + Distribution.Types.ModuleRenaming, + Distribution.Types.MungedPackageId, + Distribution.Types.MungedPackageName, + Distribution.Types.PackageDescription, + Distribution.Types.PackageId, Distribution.Types.PackageName, + Distribution.Types.PkgconfigDependency, + Distribution.Types.PkgconfigName, + Distribution.Types.SetupBuildInfo, Distribution.Types.SourceRepo, + Distribution.Types.TargetInfo, Distribution.Types.TestSuite, + Distribution.Types.TestSuiteInterface, Distribution.Types.TestType, + Distribution.Types.UnitId, Distribution.Types.UnqualComponentName, + Distribution.Types.Version, Distribution.Types.VersionRange, + Distribution.Utils.ShortText, Distribution.Verbosity, + Language.Haskell.Extension, Control.Applicative, Data.Complex, + Data.Functor.Compose, Data.Functor.Const, Data.Functor.Identity, + Data.Functor.Product, Data.Functor.Sum, Data.Monoid, + Data.Semigroup, Data.Semigroup.Internal, Data.Version, Data.Void, + GHC.Exts, GHC.Generics, GHC.IO.Exception, Data.Graph, + Data.IntMap.Internal, Data.IntSet.Internal, Data.Map.Internal, + Data.Sequence.Internal, Data.Set.Internal, Data.Tree, + Text.PrettyPrint.Annotated.HughesPJ, Text.PrettyPrint.HughesPJ, + Data.Text, Data.Text.Lazy] + [] +WARNING: file compiler/utils/ListSetOps.hs, line 58 + [Control.Applicative, Data.Functor.Const, Data.Functor.Identity, + Data.Monoid, Data.Semigroup.Internal, GHC.Generics, + GHC.IO.Exception] + [Distribution.Backpack, Distribution.Backpack.FullUnitId, + Distribution.Backpack.ModuleShape, + Distribution.Backpack.PreModuleShape, + Distribution.Backpack.ReadyComponent, + Distribution.CabalSpecVersion, Distribution.Compat.Graph, + Distribution.Compat.Semigroup, Distribution.Compiler, + Distribution.License, Distribution.ModuleName, + Distribution.SPDX.License, Distribution.SPDX.LicenseExceptionId, + Distribution.SPDX.LicenseExpression, Distribution.SPDX.LicenseId, + Distribution.SPDX.LicenseReference, + Distribution.Simple.BuildTarget, Distribution.Simple.Compiler, + Distribution.Simple.Doctest, Distribution.Simple.Haddock, + Distribution.Simple.InstallDirs, Distribution.Simple.PackageIndex, + Distribution.Simple.Program.Find, Distribution.Simple.Program.GHC, + Distribution.Simple.Program.Types, Distribution.Simple.Setup, + Distribution.System, Distribution.Types.AbiDependency, + Distribution.Types.AbiHash, Distribution.Types.Benchmark, + Distribution.Types.BenchmarkInterface, + Distribution.Types.BenchmarkType, Distribution.Types.BuildInfo, + Distribution.Types.BuildType, Distribution.Types.ComponentId, + Distribution.Types.ComponentLocalBuildInfo, + Distribution.Types.ComponentName, + Distribution.Types.ComponentRequestedSpec, + Distribution.Types.CondTree, Distribution.Types.Condition, + Distribution.Types.Dependency, Distribution.Types.ExeDependency, + Distribution.Types.Executable, Distribution.Types.ExecutableScope, + Distribution.Types.ExposedModule, Distribution.Types.ForeignLib, + Distribution.Types.ForeignLibOption, + Distribution.Types.ForeignLibType, + Distribution.Types.GenericPackageDescription, + Distribution.Types.IncludeRenaming, + Distribution.Types.InstalledPackageInfo, + Distribution.Types.LegacyExeDependency, Distribution.Types.Library, + Distribution.Types.LocalBuildInfo, Distribution.Types.Mixin, + Distribution.Types.Module, Distribution.Types.ModuleReexport, + Distribution.Types.ModuleRenaming, + Distribution.Types.MungedPackageId, + Distribution.Types.MungedPackageName, + Distribution.Types.PackageDescription, + Distribution.Types.PackageId, Distribution.Types.PackageName, + Distribution.Types.PkgconfigDependency, + Distribution.Types.PkgconfigName, + Distribution.Types.SetupBuildInfo, Distribution.Types.SourceRepo, + Distribution.Types.TargetInfo, Distribution.Types.TestSuite, + Distribution.Types.TestSuiteInterface, Distribution.Types.TestType, + Distribution.Types.UnitId, Distribution.Types.UnqualComponentName, + Distribution.Types.Version, Distribution.Types.VersionRange, + Distribution.Utils.ShortText, Distribution.Verbosity, + Language.Haskell.Extension, Control.Applicative, Data.Complex, + Data.Functor.Compose, Data.Functor.Const, Data.Functor.Identity, + Data.Functor.Product, Data.Functor.Sum, Data.Monoid, + Data.Semigroup, Data.Semigroup.Internal, Data.Version, Data.Void, + GHC.Exts, GHC.Generics, GHC.IO.Exception, Data.Graph, + Data.IntMap.Internal, Data.IntSet.Internal, Data.Map.Internal, + Data.Sequence.Internal, Data.Set.Internal, Data.Tree, + Text.PrettyPrint.Annotated.HughesPJ, Text.PrettyPrint.HughesPJ, + Data.Text, Data.Text.Lazy] +WARNING: file compiler/utils/ListSetOps.hs, line 58 + [] + [Distribution.Backpack, Distribution.Backpack.FullUnitId, + Distribution.Backpack.ModuleShape, + Distribution.Backpack.PreModuleShape, + Distribution.Backpack.ReadyComponent, + Distribution.CabalSpecVersion, Distribution.Compat.Graph, + Distribution.Compat.Semigroup, Distribution.Compiler, + Distribution.License, Distribution.ModuleName, + Distribution.SPDX.License, Distribution.SPDX.LicenseExceptionId, + Distribution.SPDX.LicenseExpression, Distribution.SPDX.LicenseId, + Distribution.SPDX.LicenseReference, + Distribution.Simple.BuildTarget, Distribution.Simple.Compiler, + Distribution.Simple.Doctest, Distribution.Simple.Haddock, + Distribution.Simple.InstallDirs, Distribution.Simple.PackageIndex, + Distribution.Simple.Program.Find, Distribution.Simple.Program.GHC, + Distribution.Simple.Program.Types, Distribution.Simple.Setup, + Distribution.System, Distribution.Types.AbiDependency, + Distribution.Types.AbiHash, Distribution.Types.Benchmark, + Distribution.Types.BenchmarkInterface, + Distribution.Types.BenchmarkType, Distribution.Types.BuildInfo, + Distribution.Types.BuildType, Distribution.Types.ComponentId, + Distribution.Types.ComponentLocalBuildInfo, + Distribution.Types.ComponentName, + Distribution.Types.ComponentRequestedSpec, + Distribution.Types.CondTree, Distribution.Types.Condition, + Distribution.Types.Dependency, Distribution.Types.ExeDependency, + Distribution.Types.Executable, Distribution.Types.ExecutableScope, + Distribution.Types.ExposedModule, Distribution.Types.ForeignLib, + Distribution.Types.ForeignLibOption, + Distribution.Types.ForeignLibType, + Distribution.Types.GenericPackageDescription, + Distribution.Types.IncludeRenaming, + Distribution.Types.InstalledPackageInfo, + Distribution.Types.LegacyExeDependency, Distribution.Types.Library, + Distribution.Types.LocalBuildInfo, Distribution.Types.Mixin, + Distribution.Types.Module, Distribution.Types.ModuleReexport, + Distribution.Types.ModuleRenaming, + Distribution.Types.MungedPackageId, + Distribution.Types.MungedPackageName, + Distribution.Types.PackageDescription, + Distribution.Types.PackageId, Distribution.Types.PackageName, + Distribution.Types.PkgconfigDependency, + Distribution.Types.PkgconfigName, + Distribution.Types.SetupBuildInfo, Distribution.Types.SourceRepo, + Distribution.Types.TargetInfo, Distribution.Types.TestSuite, + Distribution.Types.TestSuiteInterface, Distribution.Types.TestType, + Distribution.Types.UnitId, Distribution.Types.UnqualComponentName, + Distribution.Types.Version, Distribution.Types.VersionRange, + Distribution.Utils.ShortText, Distribution.Verbosity, + Language.Haskell.Extension, Control.Applicative, Data.Complex, + Data.Functor.Compose, Data.Functor.Const, Data.Functor.Identity, + Data.Functor.Product, Data.Functor.Sum, Data.Monoid, + Data.Semigroup, Data.Semigroup.Internal, Data.Version, Data.Void, + GHC.Exts, GHC.Generics, GHC.IO.Exception, Data.Graph, + Data.IntMap.Internal, Data.IntSet.Internal, Data.Map.Internal, + Data.Sequence.Internal, Data.Set.Internal, Data.Tree, + Text.PrettyPrint.Annotated.HughesPJ, Text.PrettyPrint.HughesPJ, + Data.Text, Data.Text.Lazy] +WARNING: file compiler/utils/ListSetOps.hs, line 58 + [Distribution.Backpack, Distribution.Backpack.FullUnitId, + Distribution.Backpack.ModuleShape, + Distribution.Backpack.PreModuleShape, + Distribution.Backpack.ReadyComponent, + Distribution.CabalSpecVersion, Distribution.Compat.Graph, + Distribution.Compat.Semigroup, Distribution.Compiler, + Distribution.License, Distribution.ModuleName, + Distribution.SPDX.License, Distribution.SPDX.LicenseExceptionId, + Distribution.SPDX.LicenseExpression, Distribution.SPDX.LicenseId, + Distribution.SPDX.LicenseReference, + Distribution.Simple.BuildTarget, Distribution.Simple.Compiler, + Distribution.Simple.Doctest, Distribution.Simple.Haddock, + Distribution.Simple.InstallDirs, Distribution.Simple.PackageIndex, + Distribution.Simple.Program.Find, Distribution.Simple.Program.GHC, + Distribution.Simple.Program.Types, Distribution.Simple.Setup, + Distribution.System, Distribution.Types.AbiDependency, + Distribution.Types.AbiHash, Distribution.Types.Benchmark, + Distribution.Types.BenchmarkInterface, + Distribution.Types.BenchmarkType, Distribution.Types.BuildInfo, + Distribution.Types.BuildType, Distribution.Types.ComponentId, + Distribution.Types.ComponentLocalBuildInfo, + Distribution.Types.ComponentName, + Distribution.Types.ComponentRequestedSpec, + Distribution.Types.CondTree, Distribution.Types.Condition, + Distribution.Types.Dependency, Distribution.Types.ExeDependency, + Distribution.Types.Executable, Distribution.Types.ExecutableScope, + Distribution.Types.ExposedModule, Distribution.Types.ForeignLib, + Distribution.Types.ForeignLibOption, + Distribution.Types.ForeignLibType, + Distribution.Types.GenericPackageDescription, + Distribution.Types.IncludeRenaming, + Distribution.Types.InstalledPackageInfo, + Distribution.Types.LegacyExeDependency, Distribution.Types.Library, + Distribution.Types.LocalBuildInfo, Distribution.Types.Mixin, + Distribution.Types.Module, Distribution.Types.ModuleReexport, + Distribution.Types.ModuleRenaming, + Distribution.Types.MungedPackageId, + Distribution.Types.MungedPackageName, + Distribution.Types.PackageDescription, + Distribution.Types.PackageId, Distribution.Types.PackageName, + Distribution.Types.PkgconfigDependency, + Distribution.Types.PkgconfigName, + Distribution.Types.SetupBuildInfo, Distribution.Types.SourceRepo, + Distribution.Types.TargetInfo, Distribution.Types.TestSuite, + Distribution.Types.TestSuiteInterface, Distribution.Types.TestType, + Distribution.Types.UnitId, Distribution.Types.UnqualComponentName, + Distribution.Types.Version, Distribution.Types.VersionRange, + Distribution.Utils.ShortText, Distribution.Verbosity, + Language.Haskell.Extension, Control.Applicative, Data.Complex, + Data.Functor.Compose, Data.Functor.Const, Data.Functor.Identity, + Data.Functor.Product, Data.Functor.Sum, Data.Monoid, + Data.Semigroup, Data.Semigroup.Internal, Data.Version, Data.Void, + GHC.Exts, GHC.Generics, GHC.IO.Exception, Data.Graph, + Data.IntMap.Internal, Data.IntSet.Internal, Data.Map.Internal, + Data.Sequence.Internal, Data.Set.Internal, Data.Tree, + Text.PrettyPrint.Annotated.HughesPJ, Text.PrettyPrint.HughesPJ, + Data.Text, Data.Text.Lazy] + [] *** unexpected failure for cabal09(normal) ``` This is probably orph calculation. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14759> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 19

[GHC] #11982: Typechecking fails for parallel monad comprehensions with polymorphic let
by GHC 04 Mar '19

04 Mar '19

#11982: Typechecking fails for parallel monad comprehensions with polymorphic let -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ {-# LANGUAGE MonadComprehensions, ParallelListComp #-} module Foo where foo xs ys = [ (f y True, f x 'c') | let f _ z = z, x <- xs | y <- ys ] }}} This fails with {{{ Foo.hs:5:52: error: * Cannot instantiate unification variable `t0' with a type involving foralls: forall t2 t3. t3 -> t2 -> t2 GHC doesn't yet support impredicative polymorphism * In a stmt of a monad comprehension: let f _ z = z, x <- xs | y <- ys In the expression: [(f y True, f x 'c') | let f _ z = z, x <- xs | y <- ys] In an equation for `foo': foo xs ys = [(f y True, f x 'c') | let f _ z = z, x <- xs | y <- ys] }}} NB: `ApplicativeDo` has a related problem: the implementation is quite different and has the effect of monomorphising the let-bound variable. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11982> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 21

[GHC] #14579: GeneralizedNewtypeDeriving produces ambiguously-kinded code
by GHC 04 Mar '19

04 Mar '19

#14579: GeneralizedNewtypeDeriving produces ambiguously-kinded code -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 (Type checker) | Keywords: deriving | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This program //should// compile: {{{#!hs {-# LANGUAGE GeneralizedNewtypeDeriving #-} {-# LANGUAGE TypeInType #-} module Bug where import Data.Kind import Data.Proxy newtype Wat (x :: Proxy (a :: Type)) = MkWat (Maybe a) deriving Eq newtype Glurp a = MkGlurp (Wat ('Proxy :: Proxy a)) deriving Eq }}} After all, it //should// produce this `Eq (Glurp a)` instance, which compiles without issue: {{{#!hs instance Eq a => Eq (Glurp a) where (==) = coerce @(Wat ('Proxy :: Proxy a) -> Wat ('Proxy :: Proxy a) -> Bool) @(Glurp a -> Glurp a -> Bool) (==) }}} But despite my wishful thinking, GHC does not actually do this. In fact, the code that GHC tries to generate for an `Eq (Glurp a)` instance is completely wrong: {{{ $ /opt/ghc/8.2.2/bin/ghci -ddump-deriv Bug.hs GHCi, version 8.2.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) ==================== Derived instances ==================== Derived class instances: instance forall a (x :: Data.Proxy.Proxy a). GHC.Classes.Eq a => GHC.Classes.Eq (Bug.Wat x) where (GHC.Classes.==) = GHC.Prim.coerce @(GHC.Base.Maybe a_a2wE -> GHC.Base.Maybe a_a2wE -> GHC.Types.Bool) @(Bug.Wat x_a2wF -> Bug.Wat x_a2wF -> GHC.Types.Bool) (GHC.Classes.==) (GHC.Classes./=) = GHC.Prim.coerce @(GHC.Base.Maybe a_a2wE -> GHC.Base.Maybe a_a2wE -> GHC.Types.Bool) @(Bug.Wat x_a2wF -> Bug.Wat x_a2wF -> GHC.Types.Bool) (GHC.Classes./=) instance GHC.Classes.Eq a => GHC.Classes.Eq (Bug.Glurp a) where (GHC.Classes.==) = GHC.Prim.coerce @(Bug.Wat Data.Proxy.Proxy -> Bug.Wat Data.Proxy.Proxy -> GHC.Types.Bool) @(Bug.Glurp a_a1vT -> Bug.Glurp a_a1vT -> GHC.Types.Bool) (GHC.Classes.==) (GHC.Classes./=) = GHC.Prim.coerce @(Bug.Wat Data.Proxy.Proxy -> Bug.Wat Data.Proxy.Proxy -> GHC.Types.Bool) @(Bug.Glurp a_a1vT -> Bug.Glurp a_a1vT -> GHC.Types.Bool) (GHC.Classes./=) Derived type family instances: Bug.hs:12:12: error: • Couldn't match representation of type ‘a0’ with that of ‘a’ arising from a use of ‘GHC.Prim.coerce’ ‘a’ is a rigid type variable bound by the instance declaration at Bug.hs:12:12-13 • In the expression: GHC.Prim.coerce @(Wat Proxy -> Wat Proxy -> Bool) @(Glurp a -> Glurp a -> Bool) (==) In an equation for ‘==’: (==) = GHC.Prim.coerce @(Wat Proxy -> Wat Proxy -> Bool) @(Glurp a -> Glurp a -> Bool) (==) When typechecking the code for ‘==’ in a derived instance for ‘Eq (Glurp a)’: To see the code I am typechecking, use -ddump-deriv In the instance declaration for ‘Eq (Glurp a)’ • Relevant bindings include (==) :: Glurp a -> Glurp a -> Bool (bound at Bug.hs:12:12) | 12 | deriving Eq | ^^ Bug.hs:12:12: error: • Could not deduce (Eq a0) arising from a use of ‘==’ from the context: Eq a bound by the instance declaration at Bug.hs:12:12-13 The type variable ‘a0’ is ambiguous These potential instances exist: instance forall k (s :: k). Eq (Proxy s) -- Defined in ‘Data.Proxy’ instance Eq Ordering -- Defined in ‘GHC.Classes’ instance Eq Integer -- Defined in ‘integer-gmp-1.0.1.0:GHC.Integer.Type’ ...plus 25 others ...plus 9 instances involving out-of-scope types (use -fprint-potential-instances to see them all) • In the third argument of ‘GHC.Prim.coerce’, namely ‘(==)’ In the expression: GHC.Prim.coerce @(Wat Proxy -> Wat Proxy -> Bool) @(Glurp a -> Glurp a -> Bool) (==) In an equation for ‘==’: (==) = GHC.Prim.coerce @(Wat Proxy -> Wat Proxy -> Bool) @(Glurp a -> Glurp a -> Bool) (==) When typechecking the code for ‘==’ in a derived instance for ‘Eq (Glurp a)’: To see the code I am typechecking, use -ddump-deriv | 12 | deriving Eq | ^^ Bug.hs:12:12: error: • Couldn't match representation of type ‘a1’ with that of ‘a’ arising from a use of ‘GHC.Prim.coerce’ ‘a’ is a rigid type variable bound by the instance declaration at Bug.hs:12:12-13 • In the expression: GHC.Prim.coerce @(Wat Proxy -> Wat Proxy -> Bool) @(Glurp a -> Glurp a -> Bool) (/=) In an equation for ‘/=’: (/=) = GHC.Prim.coerce @(Wat Proxy -> Wat Proxy -> Bool) @(Glurp a -> Glurp a -> Bool) (/=) When typechecking the code for ‘/=’ in a derived instance for ‘Eq (Glurp a)’: To see the code I am typechecking, use -ddump-deriv In the instance declaration for ‘Eq (Glurp a)’ • Relevant bindings include (/=) :: Glurp a -> Glurp a -> Bool (bound at Bug.hs:12:12) | 12 | deriving Eq | ^^ Bug.hs:12:12: error: • Could not deduce (Eq a1) arising from a use of ‘/=’ from the context: Eq a bound by the instance declaration at Bug.hs:12:12-13 The type variable ‘a1’ is ambiguous These potential instances exist: instance forall k (s :: k). Eq (Proxy s) -- Defined in ‘Data.Proxy’ instance Eq Ordering -- Defined in ‘GHC.Classes’ instance Eq Integer -- Defined in ‘integer-gmp-1.0.1.0:GHC.Integer.Type’ ...plus 25 others ...plus 9 instances involving out-of-scope types (use -fprint-potential-instances to see them all) • In the third argument of ‘GHC.Prim.coerce’, namely ‘(/=)’ In the expression: GHC.Prim.coerce @(Wat Proxy -> Wat Proxy -> Bool) @(Glurp a -> Glurp a -> Bool) (/=) In an equation for ‘/=’: (/=) = GHC.Prim.coerce @(Wat Proxy -> Wat Proxy -> Bool) @(Glurp a -> Glurp a -> Bool) (/=) When typechecking the code for ‘/=’ in a derived instance for ‘Eq (Glurp a)’: To see the code I am typechecking, use -ddump-deriv | 12 | deriving Eq | ^^ }}} Yikes. To see what went wrong, let's zoom in a particular part of the `-ddump-deriv` output (cleaned up a bit for presentation purposes): {{{#!hs instance Eq a => Eq (Glurp a) where (==) = coerce @(Wat 'Proxy -> Wat 'Proxy -> Bool) @(Glurp a -> Glurp a -> Bool) (==) }}} Notice that it's `Wat 'Proxy`, and not `Wat ('Proxy :: Proxy a)`! And no, that's not just a result of GHC omitting the kind information—you will see the exact same thing if you compile with `-fprint-explicit-kinds`. What's going on here? As it turns out, the types inside of those visible type applications aren't `Type`s, but rather `HsType GhcRn`s (i.e., source syntax). So what is happening is that GHC is literally producing `@(Wat 'Proxy -> Wat 'Proxy -> Bool)` //as source syntax//, not as a `Type`. This means that `'Proxy` has an underspecified kind, resulting in the numerous `The type variable ‘a0’ is ambiguous` errors you see above. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14579> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 27

[GHC] #14078: -ddump-json doesn't work well with GHCi
by GHC 04 Mar '19

04 Mar '19

#14078: -ddump-json doesn't work well with GHCi -------------------------------------+------------------------------------- Reporter: dramforever | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Currently, `:set -ddump-json` in `GHCi` causes all errors to be gathered to be written out on exit. `ghci -ddump-json` is even worse, only resulting in a `[]` being output on exit. However, I believe this completely defeats the purpose of this flag in GHCi. I expect `ghci -ddump-json` to work like this: for _each_ evaluation typed at the GHCi prompt, one JSON array is output for all messages this evaluation caused. This proposed behavior is consistent with other flags like `-ddump-simpl`, and will allow tooling to interact with GHCi nicely. Reporting this as a bug because this looks half-supported rather than unsupported, and also because of the different behaviors of `ghci -ddump- json` and `:set -ddump-json`. Sorry if it was not warranted. == Steps to reproduce `cmd>` is the shell prompt. {{{#!hs cmd> ghc --version The Glorious Glasgow Haskell Compilation System, version 8.2.1 cmd> type tmp.hs main = print 2 + 2 cmd> ghci -ddump-json tmp.hs GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( tmp.hs, interpreted ) tmp.hs:1:8: error: ? No instance for (Num (IO ())) arising from a use of ‘+’ ? In the expression: print 2 + 2 In an equation for ‘main’: main = print 2 + 2 | 1 | main = print 2 + 2 | ^^^^^^^^^^^ Failed, 0 modules loaded. Prelude> :q Leaving GHCi. [] cmd> ghci GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help Prelude> :set -ddump-json Prelude> :l tmp.hs [1 of 1] Compiling Main ( tmp.hs, interpreted ) tmp.hs:1:8: error: ? No instance for (Num (IO ())) arising from a use of ‘+’ ? In the expression: print 2 + 2 In an equation for ‘main’: main = print 2 + 2 | 1 | main = print 2 + 2 | ^^^^^^^^^^^ Failed, 0 modules loaded. Prelude> :q Leaving GHCi. [ {"span": {"file": "tmp.hs","startLine": 1,"startCol": 8,"endLine": 1,"endCol": 19},"doc": "\u2022 No instance for (Num (IO ())) arising from a use of \u2018+\u2019\n\u2022 In the expression: print 2 + 2\n In an equation for \u2018main\u2019: main = print 2 + 2","severity": "SevError","reason": null}, {"span": null,"doc": "[1 of 1] Compiling Main ( tmp.hs, interpreted )","severity": "SevOutput","reason": null}] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14078> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 11

[GHC] #9894: Presence of DWARF debug symbols doesn't result in working backtraces in GDB
by GHC 04 Mar '19

04 Mar '19

#9894: Presence of DWARF debug symbols doesn't result in working backtraces in GDB ----------------------------------+--------------------------------------- Reporter: tibbe | Owner: scpmw Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Linux Architecture: x86_64 (amd64) | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: ----------------------------------+--------------------------------------- Now when GHC can output DWARF debug symbols we need to take the remaining steps needed to get downstream tool like GDB to do something useful with it. As of today GDB cannot produce a valid stack trace for this code: {{{#!hs module Main where import System.IO f name = print $ "Hello, " ++ name {-# NOINLINE f #-} g name = f name {-# NOINLINE g #-} main = do name <- getLine g name }}} when a breakpoint is set on the line that defines `f` before the program is run. The resulting backtrace looks like: {{{ (gdb) bt #0 Main_f_info () at /tmp/Test.hs:5 #1 0x0000000000481a00 in ?? () Backtrace stopped: frame did not save the PC }}} This bug tracks the remaining work that needs to be done before this will work. Peter, what is the remaining work here? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9894> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 5

[GHC] #9910: ghc's dwarf (-g) output does not like Unicode (Char.intToDigit: not a digit 136)
by GHC 04 Mar '19

04 Mar '19

#9910: ghc's dwarf (-g) output does not like Unicode (Char.intToDigit: not a digit 136) -------------------------------------+------------------------------------- Reporter: slyfox | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Easy to reproduce as: {{{ inplace/bin/ghc-stage2 -w -g -c testsuite/tests/parser/unicode/utf8_024.hs ghc-stage2: panic! (the 'impossible' happened) (GHC version 7.9.20141219 for x86_64-unknown-linux): Char.intToDigit: not a digit 136 Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} {{{ petermw> Yes, Unicode doesn't work with DWARF yet }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9910> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 2

[GHC] #10236: DWARF unwind info is broken
by GHC 04 Mar '19

04 Mar '19

#10236: DWARF unwind info is broken -------------------------------------+------------------------------------- Reporter: | Owner: thoughtpolice | Status: new Type: bug | Milestone: 7.10.2 Priority: high | Version: 7.10.1 Component: Compiler | Operating System: Unknown/Multiple (Debugging) | Type of failure: Incorrect result Keywords: dwarf | at runtime Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: Phab:D792 | -------------------------------------+------------------------------------- As reported by `bitonic` and `petermw` on `#ghc` (April 2nd): {{{ 07:02 < bitonic> I'm trying to get a meaningful backtrace with DWARF, using <https://ghc.haskell.org/trac/ghc/wiki/DWARF> as a guide. however, all I get is `Backtrace stopped: previous frame identical to this frame (corrupt stack?)` 07:03 < bitonic> I've re-built GHC 7.10.1 using `GhcRtsHcOpts += -g` and `GhcLibHcOpts += -g`, even if I'm not sure it's even necessary 07:04 < bitonic> are there any additional steps I should take? or any way to make sure that the binary I'm generating is sane? }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10236> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 6