1. 27 Feb, 2019 1 commit
    • Vladislav Zavialov's avatar
      Treat kind/type variables identically, demolish FKTV · 5bc195b1
      Vladislav Zavialov authored
      Implements GHC Proposal #24: .../ghc-proposals/blob/master/proposals/0024-no-kind-vars.rst
      Fixes Trac #16334, Trac #16315
      
      With this patch, scoping rules for type and kind variables have been
      unified: kind variables no longer receieve special treatment. This
      simplifies both the language and the implementation.
      
      User-facing changes
      -------------------
      
      * Kind variables are no longer implicitly quantified when an explicit
        forall is used:
      
          p ::             Proxy (a :: k)    -- still accepted
          p :: forall k a. Proxy (a :: k)    -- still accepted
          p :: forall   a. Proxy (a :: k)    -- no longer accepted
      
        In other words, now we adhere to the "forall-or-nothing" rule more
        strictly.
      
        Related function: RnTypes.rnImplicitBndrs
      
      * The -Wimplicit-kind-vars warning has been deprecated.
      
      * Kind variables are no longer implicitly quantified in constructor
        declarations:
      
          data T a        = T1 (S (a :: k) | forall (b::k). T2 (S b)  -- no longer accepted
          data T (a :: k) = T1 (S (a :: k) | forall (b::k). T2 (S b)  -- still accepted
      
        Related function: RnTypes.extractRdrKindSigVars
      
      * Implicitly quantified kind variables are no longer put in front of
        other variables:
      
          f :: Proxy (a :: k) -> Proxy (b :: j)
      
          f :: forall k j (a :: k) (b :: j). Proxy a -> Proxy b   -- old order
          f :: forall k (a :: k) j (b :: j). Proxy a -> Proxy b   -- new order
      
        This is a breaking change for users of TypeApplications. Note that
        we still respect the dpendency order: 'k' before 'a', 'j' before 'b'.
        See "Ordering of specified variables" in the User's Guide.
      
        Related function: RnTypes.rnImplicitBndrs
      
      * In type synonyms and type family equations, free variables on the RHS
        are no longer implicitly quantified unless used in an outermost kind
        annotation:
      
          type T = Just (Nothing :: Maybe a)         -- no longer accepted
          type T = Just Nothing :: Maybe (Maybe a)   -- still accepted
      
        The latter form is a workaround due to temporary lack of an explicit
        quantification method. Ideally, we would write something along these
        lines:
      
          type T @a = Just (Nothing :: Maybe a)
      
        Related function: RnTypes.extractHsTyRdrTyVarsKindVars
      
      * Named wildcards in kinds are fixed (Trac #16334):
      
          x :: (Int :: _t)    -- this compiles, infers (_t ~ Type)
      
        Related function: RnTypes.partition_nwcs
      
      Implementation notes
      --------------------
      
      * One of the key changes is the removal of FKTV in RnTypes:
      
        - data FreeKiTyVars = FKTV { fktv_kis    :: [Located RdrName]
        -                          , fktv_tys    :: [Located RdrName] }
        + type FreeKiTyVars = [Located RdrName]
      
        We used to keep track of type and kind variables separately, but
        now that they are on equal footing when it comes to scoping, we
        can put them in the same list.
      
      * extract_lty and family are no longer parametrized by TypeOrKind,
        as we now do not distinguish kind variables from type variables.
      
      * PatSynExPE and the related Note [Pattern synonym existentials do not scope]
        have been removed (Trac #16315). With no implicit kind quantification,
        we can no longer trigger the error.
      
      * reportFloatingKvs and the related Note [Free-floating kind vars]
        have been removed. With no implicit kind quantification,
        we can no longer trigger the error.
      5bc195b1
  2. 24 Feb, 2019 2 commits
    • Vladislav Zavialov's avatar
      Expression/command ambiguity resolution · e61f6e35
      Vladislav Zavialov authored
      This patch removes 'HsArrApp' and 'HsArrForm' from 'HsExpr' by
      introducing a new ambiguity resolution system in the parser.
      
      Problem: there are places in the grammar where we do not know whether we
      are parsing an expression or a command:
      
      	proc x -> do { (stuff) -< x }   -- 'stuff' is an expression
      	proc x -> do { (stuff) }        -- 'stuff' is a command
      
      Until we encounter arrow syntax (-<) we don't know whether to parse
      'stuff' as an expression or a command.
      
      The old solution was to parse as HsExpr always, and rejig later:
      
      	checkCommand :: LHsExpr GhcPs -> P (LHsCmd GhcPs)
      
      This meant polluting 'HsExpr' with command-related constructors. In
      other words, limitations of the parser were affecting the AST, and
      all other code (the renamer, the typechecker) had to deal with these
      extra constructors by panicking.
      
      We fix this abstraction leak by parsing into an intermediate
      representation, 'ExpCmd':
      
      	data ExpCmdG b where
      	  ExpG :: ExpCmdG HsExpr
      	  CmdG :: ExpCmdG HsCmd
      
      	type ExpCmd = forall b. ExpCmdG b -> PV (Located (b GhcPs))
      
      	checkExp :: ExpCmd -> PV (LHsExpr GhcPs)
      	checkCmd :: ExpCmd -> PV (LHsCmd GhcPs)
      	checkExp f = f ExpG  -- interpret as an expression
      	checkCmd f = f CmdG  -- interpret as a command
      
      See Note [Ambiguous syntactic categories] for details.
      
      Now the intricacies of parsing have no effect on the hsSyn AST when it
      comes to the expression/command ambiguity.
      
      Future work: apply the same principles to the expression/pattern
      ambiguity.
      e61f6e35
    • Simon Peyton Jones's avatar
      Add AnonArgFlag to FunTy · 6cce36f8
      Simon Peyton Jones authored
      The big payload of this patch is:
      
        Add an AnonArgFlag to the FunTy constructor
        of Type, so that
          (FunTy VisArg   t1 t2) means (t1 -> t2)
          (FunTy InvisArg t1 t2) means (t1 => t2)
      
      The big payoff is that we have a simple, local test to make
      when decomposing a type, leading to many fewer calls to
      isPredTy. To me the code seems a lot tidier, and probably
      more efficient (isPredTy has to take the kind of the type).
      
      See Note [Function types] in TyCoRep.
      
      There are lots of consequences
      
      * I made FunTy into a record, so that it'll be easier
        when we add a linearity field, something that is coming
        down the road.
      
      * Lots of code gets touched in a routine way, simply because it
        pattern matches on FunTy.
      
      * I wanted to make a pattern synonym for (FunTy2 arg res), which
        picks out just the argument and result type from the record. But
        alas the pattern-match overlap checker has a heart attack, and
        either reports false positives, or takes too long.  In the end
        I gave up on pattern synonyms.
      
        There's some commented-out code in TyCoRep that shows what I
        wanted to do.
      
      * Much more clarity about predicate types, constraint types
        and (in particular) equality constraints in kinds.  See TyCoRep
        Note [Types for coercions, predicates, and evidence]
        and Note [Constraints in kinds].
      
        This made me realise that we need an AnonArgFlag on
        AnonTCB in a TyConBinder, something that was really plain
        wrong before. See TyCon Note [AnonTCB InivsArg]
      
      * When building function types we must know whether we
        need VisArg (mkVisFunTy) or InvisArg (mkInvisFunTy).
        This turned out to be pretty easy in practice.
      
      * Pretty-printing of types, esp in IfaceType, gets
        tidier, because we were already recording the (->)
        vs (=>) distinction in an ad-hoc way.  Death to
        IfaceFunTy.
      
      * mkLamType needs to keep track of whether it is building
        (t1 -> t2) or (t1 => t2).  See Type
        Note [mkLamType: dictionary arguments]
      
      Other minor stuff
      
      * Some tidy-up in validity checking involving constraints;
        Trac #16263
      6cce36f8
  3. 21 Jan, 2019 1 commit
  4. 18 Jan, 2019 1 commit
  5. 03 Dec, 2018 1 commit
    • Simon Peyton Jones's avatar
      Introduce tcTypeKind, and use it · 03d48526
      Simon Peyton Jones authored
      In the type checker Constraint and * are distinct; and the function
      that takes the kind of a type should respect that distinction
      (Trac #15971).
      
      This patch implements the change:
      
      * Introduce Type.tcTypeKind, and use it throughout the type
        inference engine
      
      * Add new Note [Kinding rules for types] for the kinding
        rules, especially for foralls.
      
      * Redefine
          isPredTy ty = tcIsConstraintKind (tcTypeKind ty)
        (it had a much more complicated definition before)
      
      Some miscellaneous refactoring
      
      * Get rid of TyCoRep.isTYPE, Kind.isTYPEApp,
        in favour of TyCoRep.kindRep, kindRep_maybe
      
      * Rename Type.getRuntimeRepFromKind_maybe
        to getRuntimeRep_maybe
      
      I did some spot-checks on compiler perf, and it really doesn't
      budge (as expected).
      03d48526
  6. 29 Nov, 2018 1 commit
    • Simon Peyton Jones's avatar
      Taming the Kind Inference Monster · 2257a86d
      Simon Peyton Jones authored
      My original goal was (Trac #15809) to move towards using level numbers
      as the basis for deciding which type variables to generalise, rather
      than searching for the free varaibles of the environment.  However
      it has turned into a truly major refactoring of the kind inference
      engine.
      
      Let's deal with the level-numbers part first:
      
      * Augment quantifyTyVars to calculate the type variables to
        quantify using level numbers, and compare the result with
        the existing approach.  That is; no change in behaviour,
        just a WARNing if the two approaches give different answers.
      
      * To do this I had to get the level number right when calling
        quantifyTyVars, and this entailed a bit of care, especially
        in the code for kind-checking type declarations.
      
      * However, on the way I was able to eliminate or simplify
        a number of calls to solveEqualities.
      
      This work is incomplete: I'm not /using/ level numbers yet.
      When I subsequently get rid of any remaining WARNings in
      quantifyTyVars, that the level-number answers differ from
      the current answers, then I can rip out the current
      "free vars of the environment" stuff.
      
      Anyway, this led me into deep dive into kind inference for type and
      class declarations, which is an increasingly soggy part of GHC.
      Richard already did some good work recently in
      
         commit 5e45ad10
         Date:   Thu Sep 13 09:56:02 2018 +0200
      
          Finish fix for #14880.
      
          The real change that fixes the ticket is described in
          Note [Naughty quantification candidates] in TcMType.
      
      but I kept turning over stones. So this patch has ended up
      with a pretty significant refactoring of that code too.
      
      Kind inference for types and classes
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      
      * Major refactoring in the way we generalise the inferred kind of
        a TyCon, in kcTyClGroup.  Indeed, I made it into a new top-level
        function, generaliseTcTyCon.  Plus a new Note to explain it
        Note [Inferring kinds for type declarations].
      
      * We decided (Trac #15592) not to treat class type variables specially
        when dealing with Inferred/Specified/Required for associated types.
        That simplifies things quite a bit. I also rewrote
        Note [Required, Specified, and Inferred for types]
      
      * Major refactoring of the crucial function kcLHsQTyVars:
        I split it into
             kcLHsQTyVars_Cusk  and  kcLHsQTyVars_NonCusk
        because the two are really quite different. The CUSK case is
        almost entirely rewritten, and is much easier because of our new
        decision not to treat the class variables specially
      
      * I moved all the error checks from tcTyClTyVars (which was a bizarre
        place for it) into generaliseTcTyCon and/or the CUSK case of
        kcLHsQTyVars.  Now tcTyClTyVars is extremely simple.
      
      * I got rid of all the all the subtleties in tcImplicitTKBndrs. Indeed
        now there is no difference between tcImplicitTKBndrs and
        kcImplicitTKBndrs; there is now a single bindImplicitTKBndrs.
        Same for kc/tcExplicitTKBndrs.  None of them monkey with level
        numbers, nor build implication constraints.  scopeTyVars is gone
        entirely, as is kcLHsQTyVarBndrs. It's vastly simpler.
      
        I found I could get rid of kcLHsQTyVarBndrs entirely, in favour of
        the bnew bindExplicitTKBndrs.
      
      Quantification
      ~~~~~~~~~~~~~~
      * I now deal with the "naughty quantification candidates"
        of the previous patch in candidateQTyVars, rather than in
        quantifyTyVars; see Note [Naughty quantification candidates]
        in TcMType.
      
        I also killed off closeOverKindsCQTvs in favour of the same
        strategy that we use for tyCoVarsOfType: namely, close over kinds
        at the occurrences.
      
        And candidateQTyVars no longer needs a gbl_tvs argument.
      
      * Passing the ContextKind, rather than the expected kind itself,
        to tc_hs_sig_type_and_gen makes it easy to allocate the expected
        result kind (when we are in inference mode) at the right level.
      
      Type families
      ~~~~~~~~~~~~~~
      * I did a major rewrite of the impenetrable tcFamTyPats. The result
        is vastly more comprehensible.
      
      * I got rid of kcDataDefn entirely, quite a big function.
      
      * I re-did the way that checkConsistentFamInst works, so
        that it allows alpha-renaming of invisible arguments.
      
      * The interaction of kind signatures and family instances is tricky.
          Type families: see Note [Apparently-nullary families]
          Data families: see Note [Result kind signature for a data family instance]
                         and Note [Eta-reduction for data families]
      
      * The consistent instantation of an associated type family is tricky.
        See Note [Checking consistent instantiation] and
            Note [Matching in the consistent-instantation check]
        in TcTyClsDecls.  It's now checked in TcTyClsDecls because that is
        when we have the relevant info to hand.
      
      * I got tired of the compromises in etaExpandFamInst, so I did the
        job properly by adding a field cab_eta_tvs to CoAxBranch.
        See Coercion.etaExpandCoAxBranch.
      
      tcInferApps and friends
      ~~~~~~~~~~~~~~~~~~~~~~~
      * I got rid of the mysterious and horrible ClsInstInfo argument
        to tcInferApps, checkExpectedKindX, and various checkValid
        functions.  It was horrible!
      
      * I got rid of [Type] result of tcInferApps.  This list was used
        only in tcFamTyPats, when checking the LHS of a type instance;
        and if there is a cast in the middle, the list is meaningless.
        So I made tcInferApps simpler, and moved the complexity
        (not much) to tcInferApps.
      
        Result: tcInferApps is now pretty comprehensible again.
      
      * I refactored the many function in TcMType that instantiate skolems.
      
      Smaller things
      
      * I rejigged the error message in checkValidTelescope; I think it's
        quite a bit better now.
      
      * checkValidType was not rejecting constraints in a kind signature
           forall (a :: Eq b => blah). blah2
        That led to further errors when we then do an ambiguity check.
        So I make checkValidType reject it more aggressively.
      
      * I killed off quantifyConDecl, instead calling kindGeneralize
        directly.
      
      * I fixed an outright bug in tyCoVarsOfImplic, where we were not
        colleting the tyvar of the kind of the skolems
      
      * Renamed ClsInstInfo to AssocInstInfo, and made it into its
        own data type
      
      * Some fiddling around with pretty-printing of family
        instances which was trickier than I thought.  I wanted
        wildcards to print as plain "_" in user messages, although
        they each need a unique identity in the CoAxBranch.
      
      Some other oddments
      
      * Refactoring around the trace messages from reportUnsolved.
      * A bit of extra tc-tracing in TcHsSyn.commitFlexi
      
      This patch fixes a raft of bugs, and includes tests for them.
      
       * #14887
       * #15740
       * #15764
       * #15789
       * #15804
       * #15817
       * #15870
       * #15874
       * #15881
      2257a86d
  7. 22 Nov, 2018 1 commit
    • David Eichmann's avatar
      Fix unused-import warnings · 6353efc7
      David Eichmann authored
      This patch fixes a fairly long-standing bug (dating back to 2015) in
      RdrName.bestImport, namely
      
         commit 9376249b
         Author: Simon Peyton Jones <simonpj@microsoft.com>
         Date:   Wed Oct 28 17:16:55 2015 +0000
      
         Fix unused-import stuff in a better way
      
      In that patch got the sense of the comparison back to front, and
      thereby failed to implement the unused-import rules described in
        Note [Choosing the best import declaration] in RdrName
      
      This led to Trac #13064 and #15393
      
      Fixing this bug revealed a bunch of unused imports in libraries;
      the ones in the GHC repo are part of this commit.
      
      The two important changes are
      
      * Fix the bug in bestImport
      
      * Modified the rules by adding (a) in
           Note [Choosing the best import declaration] in RdrName
        Reason: the previosu rules made Trac #5211 go bad again.  And
        the new rule (a) makes sense to me.
      
      In unravalling this I also ended up doing a few other things
      
      * Refactor RnNames.ImportDeclUsage to use a [GlobalRdrElt] for the
        things that are used, rather than [AvailInfo]. This is simpler
        and more direct.
      
      * Rename greParentName to greParent_maybe, to follow GHC
        naming conventions
      
      * Delete dead code RdrName.greUsedRdrName
      
      Bumps a few submodules.
      
      Reviewers: hvr, goldfire, bgamari, simonmar, jrtc27
      
      Subscribers: rwbarton, carter
      
      Differential Revision: https://phabricator.haskell.org/D5312
      6353efc7
  8. 27 Oct, 2018 1 commit
    • mayac's avatar
      More explicit foralls (GHC Proposal 0007) · 512eeb9b
      mayac authored
      Allow the user to explicitly bind type/kind variables in type and data
      family instances (including associated instances), closed type family
      equations, and RULES pragmas. Follows the specification of GHC
      Proposal 0007, also fixes #2600. Advised by Richard Eisenberg.
      
      This modifies the Template Haskell AST -- old code may break!
      
      Other Changes:
      - convert HsRule to a record
      - make rnHsSigWcType more general
      - add repMaybe to DsMeta
      
      Includes submodule update for Haddock.
      
      Test Plan: validate
      
      Reviewers: goldfire, bgamari, alanz
      
      Subscribers: simonpj, RyanGlScott, goldfire, rwbarton,
                   thomie, mpickering, carter
      
      GHC Trac Issues: #2600, #14268
      
      Differential Revision: https://phabricator.haskell.org/D4894
      512eeb9b
  9. 25 Oct, 2018 1 commit
    • Simon Peyton Jones's avatar
      Remove a zonkTcTyVarToTyVar · 29978ef1
      Simon Peyton Jones authored
      This patch fixes Trac #15778 by removing a zonkTcTyVarToTyVar
      from tcHsSigType.
      
      Nww that a pattern-bound type variable can refer to a type, it's
      obvoiusly wrong to expect it to be a TyVar!  Moreover, that zonk
      is entirely unnecessary.
      
      I added a new Note [Type variables in the type environment]
      in TcRnTypes
      29978ef1
  10. 24 Oct, 2018 3 commits
  11. 05 Oct, 2018 1 commit
  12. 04 Oct, 2018 1 commit
    • Simon Peyton Jones's avatar
      Fail fast on pattern synonyms · 9ebfa03d
      Simon Peyton Jones authored
      We were recovering too eagerly from errors in pattern-synonym
      type inference, leading to a cascade of confusing follow up errors
      (Trac #15685, #15692).
      
      The underlying issue is that a pattern synonym should have a closed,
      fixed type, with no unification variables in it.  But it wasn't!
      
      Fixing this made me change the interface to simplifyInfer slightly.
      Instead of /emitting/ a residual implication constraint, it
      now /returns/ it, so that the caller can decide what to do.
      9ebfa03d
  13. 15 Sep, 2018 1 commit
    • Ningning Xie's avatar
      Coercion Quantification · ea5ade34
      Ningning Xie authored
      This patch corresponds to #15497.
      
      According to https://ghc.haskell.org/trac/ghc/wiki/DependentHaskell/Phase2,
       we would like to have coercion quantifications back. This will
      allow us to migrate (~#) to be homogeneous, instead of its current
      heterogeneous definition. This patch is (lots of) plumbing only. There
      should be no user-visible effects.
      
      An overview of changes:
      
      - Both `ForAllTy` and `ForAllCo` can quantify over coercion variables,
      but only in *Core*. All relevant functions are updated accordingly.
      - Small changes that should be irrelevant to the main task:
          1. removed dead code `mkTransAppCo` in Coercion
          2. removed out-dated Note Computing a coercion kind and
             roles in Coercion
          3. Added `Eq4` in Note Respecting definitional equality in
             TyCoRep, and updated `mkCastTy` accordingly.
          4. Various updates and corrections of notes and typos.
      - Haddock submodule needs to be changed too.
      
      Acknowledgments:
      This work was completed mostly during Ningning Xie's Google Summer
      of Code, sponsored by Google. It was advised by Richard Eisenberg,
      supported by NSF grant 1704041.
      
      Test Plan: ./validate
      
      Reviewers: goldfire, simonpj, bgamari, hvr, erikd, simonmar
      
      Subscribers: RyanGlScott, monoidal, rwbarton, carter
      
      GHC Trac Issues: #15497
      
      Differential Revision: https://phabricator.haskell.org/D5054
      ea5ade34
  14. 13 Sep, 2018 1 commit
  15. 24 Aug, 2018 1 commit
  16. 21 Aug, 2018 1 commit
    • Andreas Klebinger's avatar
      Replace most occurences of foldl with foldl'. · 09c1d5af
      Andreas Klebinger authored
      This patch adds foldl' to GhcPrelude and changes must occurences
      of foldl to foldl'. This leads to better performance especially
      for quick builds where GHC does not perform strictness analysis.
      
      It does change strictness behaviour when we use foldl' to turn
      a argument list into function applications. But this is only a
      drawback if code looks ONLY at the last argument but not at the first.
      And as the benchmarks show leads to fewer allocations in practice
      at O2.
      
      Compiler performance for Nofib:
      
      O2 Allocations:
              -1 s.d.                -----            -0.0%
              +1 s.d.                -----            -0.0%
              Average                -----            -0.0%
      
      O2 Compile Time:
              -1 s.d.                -----            -2.8%
              +1 s.d.                -----            +1.3%
              Average                -----            -0.8%
      
      O0 Allocations:
              -1 s.d.                -----            -0.2%
              +1 s.d.                -----            -0.1%
              Average                -----            -0.2%
      
      Test Plan: ci
      
      Reviewers: goldfire, bgamari, simonmar, tdammers, monoidal
      
      Reviewed By: bgamari, monoidal
      
      Subscribers: tdammers, rwbarton, thomie, carter
      
      Differential Revision: https://phabricator.haskell.org/D4929
      09c1d5af
  17. 17 Aug, 2018 1 commit
    • Joachim Breitner's avatar
      Rename SigTv to TyVarTv (#15480) · a50244c6
      Joachim Breitner authored
      because since #15050, these are no longer used in pattern SIGnatures,
      but still in other places where meta-variables should only be unified
      with TYpe VARiables.
      
      I also found mentions of `SigTv` in parts of the renamer and desugarer
      that do not seem to directly relate to `SigTv` as used in the type
      checker, but rather to uses of `forall a.` in type signatures. I renamed
      these to `ScopedTv`.
      
      Differential Revision: https://phabricator.haskell.org/D5074
      a50244c6
  18. 25 Jul, 2018 1 commit
  19. 24 Jul, 2018 1 commit
    • Ryan Scott's avatar
      Suppress -Winaccessible-code in derived code · 44a7b9ba
      Ryan Scott authored
      Summary:
      It's rather unfortunate that derived code can produce inaccessible
      code warnings (as demonstrated in #8128, #8740, and #15398), since
      the programmer has no control over the generated code. This patch
      aims to suppress `-Winaccessible-code` in all derived code. It
      accomplishes this by doing the following:
      
      * Generalize the `ic_env :: TcLclEnv` field of `Implication` to
        be of type `Env TcGblEnc TcLclEnv` instead. This way, it also
        captures `DynFlags`, which record the flag state at the time
        the `Implication` was created.
      * When typechecking derived code, turn off `-Winaccessible-code`.
        This way, any insoluble given `Implication`s that are created when
        typechecking this derived code will remember that
        `-Winaccessible-code` was disabled.
      * During error reporting, consult the `DynFlags` of an
        `Implication` before making the decision to report an inaccessible
        code warning.
      
      Test Plan: make test TEST="T8128 T8740 T15398"
      
      Reviewers: simonpj, bgamari
      
      Reviewed By: simonpj
      
      Subscribers: monoidal, rwbarton, thomie, carter
      
      GHC Trac Issues: #8128, #8740, #15398
      
      Differential Revision: https://phabricator.haskell.org/D4993
      44a7b9ba
  20. 22 Jun, 2018 1 commit
    • Simon Peyton Jones's avatar
      Instances in no-evidence implications · 32eb4199
      Simon Peyton Jones authored
      Trac #15290 showed that it's possible that we might attempt to use a
      quantified constraint to solve an equality in a situation where we
      don't have anywhere to put the evidence bindings.  This made GHC crash.
      
      This patch stops the crash, but still rejects the pogram.  See
      Note [Instances in no-evidence implications] in TcInteract.
      
      Finding this bug revealed another lurking bug:
      
      * An infelicity in the treatment of superclasses -- we were expanding
        them locally at the leaves, rather than at their binding site; see
        (3a) in Note [The superclass story].
      
        As a consequence, TcRnTypes.superclassesMightHelp must look inside
        implications.
      
      In more detail:
      
      * Stop the crash, by making TcInteract.chooseInstance test for
        the no-evidence-bindings case.  In that case we simply don't
        use the instance.  This entailed a slight change to the type
        of chooseInstance.
      
      * Make TcSMonad.getPendingScDicts (now renamed getPendingGivenScs)
        return only Givens from the /current level/; and make
        TcRnTypes.superClassesMightHelp look inside implications.
      
      * Refactor the simpl_loop and superclass-expansion stuff in
        TcSimplify.  The logic is much easier to understand now, and
        has less duplication.
      32eb4199
  21. 18 Jun, 2018 1 commit
  22. 17 Jun, 2018 1 commit
    • Ryan Scott's avatar
      Provide a better error message for unpromotable data constructor contexts · c6375411
      Ryan Scott authored
      Trac #14845 brought to light a corner case where a data
      constructor could not be promoted (even with `-XTypeInType`) due to
      an unpromotable constraint in its context. However, the error message
      was less than helpful, so this patch adds an additional check to
      `tcTyVar` catch unpromotable data constructors like these //before//
      they're promoted, and to give a sensible error message in such cases.
      
      Test Plan: make test TEST="T13895 T14845"
      
      Reviewers: simonpj, goldfire, bgamari
      
      Reviewed By: bgamari
      
      Subscribers: rwbarton, thomie, carter
      
      GHC Trac Issues: #13895, #14845
      
      Differential Revision: https://phabricator.haskell.org/D4728
      c6375411
  23. 14 Jun, 2018 1 commit
    • Vladislav Zavialov's avatar
      Embrace -XTypeInType, add -XStarIsType · d650729f
      Vladislav Zavialov authored
      Summary:
      Implement the "Embrace Type :: Type" GHC proposal,
      .../ghc-proposals/blob/master/proposals/0020-no-type-in-type.rst
      
      GHC 8.0 included a major change to GHC's type system: the Type :: Type
      axiom. Though casual users were protected from this by hiding its
      features behind the -XTypeInType extension, all programs written in GHC
      8+ have the axiom behind the scenes. In order to preserve backward
      compatibility, various legacy features were left unchanged. For example,
      with -XDataKinds but not -XTypeInType, GADTs could not be used in types.
      Now these restrictions are lifted and -XTypeInType becomes a redundant
      flag that will be eventually deprecated.
      
      * Incorporate the features currently in -XTypeInType into the
        -XPolyKinds and -XDataKinds extensions.
      * Introduce a new extension -XStarIsType to control how to parse * in
        code and whether to print it in error messages.
      
      Test Plan: Validate
      
      Reviewers: goldfire, hvr, bgamari, alanz, simonpj
      
      Reviewed By: goldfire, simonpj
      
      Subscribers: rwbarton, thomie, mpickering, carter
      
      GHC Trac Issues: #15195
      
      Differential Revision: https://phabricator.haskell.org/D4748
      d650729f
  24. 04 Jun, 2018 1 commit
    • Simon Peyton Jones's avatar
      Implement QuantifiedConstraints · 7df58960
      Simon Peyton Jones authored
      We have wanted quantified constraints for ages and, as I hoped,
      they proved remarkably simple to implement.   All the machinery was
      already in place.
      
      The main ticket is Trac #2893, but also relevant are
        #5927
        #8516
        #9123 (especially!  higher kinded roles)
        #14070
        #14317
      
      The wiki page is
        https://ghc.haskell.org/trac/ghc/wiki/QuantifiedConstraints
      which in turn contains a link to the GHC Proposal where the change
      is specified.
      
      Here is the relevant Note:
      
      Note [Quantified constraints]
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      The -XQuantifiedConstraints extension allows type-class contexts like
      this:
      
        data Rose f x = Rose x (f (Rose f x))
      
        instance (Eq a, forall b. Eq b => Eq (f b))
              => Eq (Rose f a)  where
          (Rose x1 rs1) == (Rose x2 rs2) = x1==x2 && rs1 >= rs2
      
      Note the (forall b. Eq b => Eq (f b)) in the instance contexts.
      This quantified constraint is needed to solve the
       [W] (Eq (f (Rose f x)))
      constraint which arises form the (==) definition.
      
      Here are the moving parts
        * Language extension {-# LANGUAGE QuantifiedConstraints #-}
          and add it to ghc-boot-th:GHC.LanguageExtensions.Type.Extension
      
        * A new form of evidence, EvDFun, that is used to discharge
          such wanted constraints
      
        * checkValidType gets some changes to accept forall-constraints
          only in the right places.
      
        * Type.PredTree gets a new constructor ForAllPred, and
          and classifyPredType analyses a PredType to decompose
          the new forall-constraints
      
        * Define a type TcRnTypes.QCInst, which holds a given
          quantified constraint in the inert set
      
        * TcSMonad.InertCans gets an extra field, inert_insts :: [QCInst],
          which holds all the Given forall-constraints.  In effect,
          such Given constraints are like local instance decls.
      
        * When trying to solve a class constraint, via
          TcInteract.matchInstEnv, use the InstEnv from inert_insts
          so that we include the local Given forall-constraints
          in the lookup.  (See TcSMonad.getInstEnvs.)
      
        * topReactionsStage calls doTopReactOther for CIrredCan and
          CTyEqCan, so they can try to react with any given
          quantified constraints (TcInteract.matchLocalInst)
      
        * TcCanonical.canForAll deals with solving a
          forall-constraint.  See
             Note [Solving a Wanted forall-constraint]
             Note [Solving a Wanted forall-constraint]
      
        * We augment the kick-out code to kick out an inert
          forall constraint if it can be rewritten by a new
          type equality; see TcSMonad.kick_out_rewritable
      
      Some other related refactoring
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      
      * Move SCC on evidence bindings to post-desugaring, which fixed
        #14735, and is generally nicer anyway because we can use
        existing CoreSyn free-var functions.  (Quantified constraints
        made the free-vars of an ev-term a bit more complicated.)
      
      * In LookupInstResult, replace GenInst with OneInst and NotSure,
        using the latter for multiple matches and/or one or more
        unifiers
      7df58960
  25. 02 Jun, 2018 1 commit
    • Ben Gamari's avatar
      vectorise: Put it out of its misery · faee23bb
      Ben Gamari authored
      Poor DPH and its vectoriser have long been languishing; sadly it seems there is
      little chance that the effort will be rekindled. Every few years we discuss
      what to do with this mass of code and at least once we have agreed that it
      should be archived on a branch and removed from `master`. Here we do just that,
      eliminating heaps of dead code in the process.
      
      Here we drop the ParallelArrays extension, the vectoriser, and the `vector` and
      `primitive` submodules.
      
      Test Plan: Validate
      
      Reviewers: simonpj, simonmar, hvr, goldfire, alanz
      
      Reviewed By: simonmar
      
      Subscribers: goldfire, rwbarton, thomie, mpickering, carter
      
      Differential Revision: https://phabricator.haskell.org/D4761
      faee23bb
  26. 30 May, 2018 1 commit
    • Matthías Páll Gissurarson's avatar
      Improved Valid Hole Fits · e0b44e2e
      Matthías Páll Gissurarson authored
      I've changed the name from `Valid substitutions` to `Valid hole fits`,
      since "substitution" already has a well defined meaning within the
      theory. As part of this change, the flags and output is reanamed, with
      substitution turning into hole-fit in most cases. "hole fit" was already
      used internally in the code, it's clear and shouldn't cause any
      confusion.
      
      In this update, I've also reworked how we manage side-effects in the
      hole we are considering.
      
      This allows us to consider local bindings such as where clauses and
      arguments to functions, suggesting e.g. `a` for `head (x:xs) where head
      :: [a] -> a`.
      
      It also allows us to find suggestions such as `maximum` for holes of
      type `Ord a => a -> [a]`, and `max` when looking for a match for the
      hole in `g = foldl1 _`, where `g :: Ord a => [a] -> a`.
      
      We also show much improved output for refinement hole fits, and
      fixes #14990. We now show the correct type of the function, but we also
      now show what the arguments to the function should be e.g. `foldl1 (_ ::
      Integer -> Integer -> Integer)` when looking for `[Integer] -> Integer`.
      
      I've moved the bulk of the code from `TcErrors.hs` to a new file,
      `TcHoleErrors.hs`, since it was getting too big to not live on it's own.
      
      This addresses the considerations raised in #14969, and takes proper
      care to set the `tcLevel` of the variables to the right level before
      passing it to the simplifier.
      
      We now also zonk the suggestions properly, which improves the output of
      the refinement hole fits considerably.
      
      This also filters out suggestions from the `GHC.Err` module, since even
      though `error` and `undefined` are indeed valid hole fits, they are
      "trivial", and almost never useful to the user.
      
      We now find the hole fits using the proper manner, namely by solving
      nested implications. This entails that the givens are passed along using
      the implications the hole was nested in, which in turn should mean that
      there will be fewer weird bugs in the typed holes.
      
      I've also added a new sorting method (as suggested by SPJ) and sort by
      the size of the types needed to turn the hole fits into the type of the
      hole. This gives a reasonable approximation to relevance, and is much
      faster than the subsumption check. I've also added a flag to toggle
      whether to use this new sorting algorithm (as is done by default) or the
      subsumption algorithm. This fixes #14969
      
      I've also added documentation for these new flags and update the
      documentation according to the new output.
      
      Reviewers: bgamari, goldfire
      
      Reviewed By: bgamari
      
      Subscribers: simonpj, rwbarton, thomie, carter
      
      GHC Trac Issues: #14969, #14990, #10946
      
      Differential Revision: https://phabricator.haskell.org/D4444
      e0b44e2e
  27. 21 May, 2018 1 commit
    • Simon Peyton Jones's avatar
      Make dischargeFmv handle Deriveds · 57858fc8
      Simon Peyton Jones authored
      A Derived CFunEqCan does not "own" its FlatMetaTv (fmv), and should not
      update it.  But one caller (canCFunEqCan) was failing to satisfy the
      precondition to dischargeFmv, which led to a crash (Trac #15170).
      
      I fixed this by making dischargeFmv handle Deriveds (to avoid forcing
      each caller to do so separately).
      
      NB: this does not completely fix the original #15170 bug, but I'll
      explain that on the ticket.  The test case for this patch is actually
      the program in comment:1.
      57858fc8
  28. 18 May, 2018 2 commits
    • Simon Peyton Jones's avatar
      Debug tracing only · 5a7c657e
      Simon Peyton Jones authored
      5a7c657e
    • Simon Peyton Jones's avatar
      Orient TyVar/TyVar equalities with deepest on the left · 2bbdd00c
      Simon Peyton Jones authored
      Trac #15009 showed that, for Given TyVar/TyVar equalities, we really
      want to orient them with the deepest-bound skolem on the left. As it
      happens, we also want to do the same for Wanteds, but for a different
      reason (more likely to be touchable).  Either way, deepest wins:
      see TcUnify Note [Deeper level on the left].
      
      This observation led me to some significant changes:
      
      * A SkolemTv already had a TcLevel, but the level wasn't really being
        used.   Now it is!
      
      * I updated added invariant (SkolInf) to TcType
        Note [TcLevel and untouchable type variables], documenting that
        the level number of all the ic_skols should be the same as the
        ic_tclvl of the implication
      
      * FlatSkolTvs and FlatMetaTvs previously had a dummy level-number of
        zero, which messed the scheme up.   Now they get a level number the
        same way as all other TcTyVars, instead of being a special case.
      
      * To make sure that FlatSkolTvs and FlatMetaTvs are untouchable (which
        was previously done via their magic zero level) isTouchableMetaTyVar
        just tests for those two cases.
      
      * TcUnify.swapOverTyVars is the crucial orientation function; see the
        new Note [TyVar/TyVar orientation].  I completely rewrote this function,
        and it's now much much easier to understand.
      
      I ended up doing some related refactoring, of course
      
      * I noticed that tcImplicitTKBndrsX and tcExplicitTKBndrsX were doing
        a lot of useless work in the case where there are no skolems; I
        added a fast-patch
      
      * Elminate the un-used tcExplicitTKBndrsSig; and thereby get rid of
        the higher-order parameter to tcExpliciTKBndrsX.
      
      * Replace TcHsType.emitTvImplication with TcUnify.checkTvConstraints,
        by analogy with TcUnify.checkConstraints.
      
      * Inline TcUnify.buildImplication into its only call-site in
        TcUnify.checkConstraints
      
      * TcS.buildImplication becomes TcS.CheckConstraintsTcS, with a
        simpler API
      
      * Now that we have NoEvBindsVar we have no need of termEvidenceAllowed;
        nuke the latter, adding Note [No evidence bindings] to TcEvidence.
      2bbdd00c
  29. 17 May, 2018 1 commit
    • Simon Marlow's avatar
      Fix GHCi space leaks (#15111) · f27e4f62
      Simon Marlow authored
      Summary:
      There were a number of leaks causing previously loaded modules to be
      retained after a new `:load`.  This fixes enough leaks to get the
      tests to pass from D4658.
      
      Test Plan: See new tests in D4658
      
      Reviewers: niteria, bgamari, simonpj, erikd
      
      Subscribers: thomie, carter
      
      GHC Trac Issues: #15111
      
      Differential Revision: https://phabricator.haskell.org/D4659
      f27e4f62
  30. 27 Apr, 2018 1 commit
    • Alan Zimmerman's avatar
      TTG : complete for balance of hsSyn AST · c3823cba
      Alan Zimmerman authored
      Summary:
      - remove PostRn/PostTc fields
      - remove the HsVect In/Out distinction for Type, Class and Instance
      - remove PlaceHolder in favour of NoExt
      - Simplify OutputableX constraint
      
      Updates haddock submodule
      
      Test Plan: ./validate
      
      Reviewers: goldfire, bgamari
      
      Subscribers: goldfire, thomie, mpickering, carter
      
      Differential Revision: https://phabricator.haskell.org/D4625
      c3823cba
  31. 09 Apr, 2018 1 commit
  32. 01 Apr, 2018 2 commits
    • Richard Eisenberg's avatar
      Clarify comments around dropping Derived constraints · 1845d1bc
      Richard Eisenberg authored
      [skip ci]
      1845d1bc
    • Richard Eisenberg's avatar
      Track type variable scope more carefully. · faec8d35
      Richard Eisenberg authored
      The main job of this commit is to track more accurately the scope
      of tyvars introduced by user-written foralls. For example, it would
      be to have something like this:
      
        forall a. Int -> (forall k (b :: k). Proxy '[a, b]) -> Bool
      
      In that type, a's kind must be k, but k isn't in scope. We had a
      terrible way of doing this before (not worth repeating or describing
      here, but see the old tcImplicitTKBndrs and friends), but now
      we have a principled approach: make an Implication when kind-checking
      a forall. Doing so then hooks into the existing machinery for
      preventing skolem-escape, performing floating, etc. This also means
      that we bump the TcLevel whenever going into a forall.
      
      The new behavior is done in TcHsType.scopeTyVars, but see also
      TcHsType.tc{Im,Ex}plicitTKBndrs, which have undergone significant
      rewriting. There are several Notes near there to guide you. Of
      particular interest there is that Implication constraints can now
      have skolems that are out of order; this situation is reported in
      TcErrors.
      
      A major consequence of this is a slightly tweaked process for type-
      checking type declarations. The new Note [Use SigTvs in kind-checking
      pass] in TcTyClsDecls lays it out.
      
      The error message for dependent/should_fail/TypeSkolEscape has become
      noticeably worse. However, this is because the code in TcErrors goes to
      some length to preserve pre-8.0 error messages for kind errors. It's time
      to rip off that plaster and get rid of much of the kind-error-specific
      error messages. I tried this, and doing so led to a lovely error message
      for TypeSkolEscape. So: I'm accepting the error message quality regression
      for now, but will open up a new ticket to fix it, along with a larger
      error-message improvement I've been pondering. This applies also to
      dependent/should_fail/{BadTelescope2,T14066,T14066e}, polykinds/T11142.
      
      Other minor changes:
       - isUnliftedTypeKind didn't look for tuples and sums. It does now.
      
       - check_type used check_arg_type on both sides of an AppTy. But the left
         side of an AppTy isn't an arg, and this was causing a bad error message.
         I've changed it to use check_type on the left-hand side.
      
       - Some refactoring around when we print (TYPE blah) in error messages.
         The changes decrease the times when we do so, to good effect.
         Of course, this is still all controlled by
         -fprint-explicit-runtime-reps
      
      Fixes #14066 #14749
      
      Test cases: dependent/should_compile/{T14066a,T14749},
                  dependent/should_fail/T14066{,c,d,e,f,g,h}
      faec8d35
  33. 26 Mar, 2018 1 commit
    • Richard Eisenberg's avatar
      Fix #12919 by making the flattener homegeneous. · e3dbb44f
      Richard Eisenberg authored
      This changes a key invariant of the flattener. Previously,
      flattening a type meant flattening its kind as well. But now,
      flattening is always homogeneous -- that is, the kind of the
      flattened type is the same as the kind of the input type.
      This is achieved by various wizardry in the TcFlatten.flatten_many
      function, as described in Note [flatten_many].
      
      There are several knock-on effects, including some refactoring
      in the canonicalizer to take proper advantage of the flattener's
      changed behavior. In particular, the tyvar case of can_eq_nc' no
      longer needs to take casts into account.
      
      Another effect is that flattening a tyconapp might change it
      into a casted tyconapp. This might happen if the result kind
      of the tycon contains a variable, and that variable changes
      during flattening. Because the flattener is homogeneous, it tacks
      on a cast to keep the tyconapp kind the same. However, this
      is problematic when flattening CFunEqCans, which need to have
      an uncasted tyconapp on the LHS and must remain homogeneous.
      The solution is a more involved canCFunEqCan, described in
      Note [canCFunEqCan].
      
      This patch fixes #13643 (as tested in typecheck/should_compile/T13643)
      and the panic in typecheck/should_compile/T13822 (as reported in #14024).
      Actually, there were two bugs in T13822: the first was just some
      incorrect logic in tryFill (part of the unflattener) -- also fixed
      in this patch -- and the other was the main bug fixed in this ticket.
      
      The changes in this patch exposed a long-standing flaw in OptCoercion,
      in that breaking apart an AppCo sometimes has unexpected effects on
      kinds. See new Note [EtaAppCo] in OptCoercion, which explains the
      problem and fix.
      
      Also here is a reversion of the major change in
      09bf135a, affecting ctEvCoercion.
      It turns out that making the flattener homogeneous changes the
      invariants on the algorithm, making the change in that patch
      no longer necessary.
      
      This patch also fixes:
        #14038 (dependent/should_compile/T14038)
        #13910 (dependent/should_compile/T13910)
        #13938 (dependent/should_compile/T13938)
        #14441 (typecheck/should_compile/T14441)
        #14556 (dependent/should_compile/T14556)
        #14720 (dependent/should_compile/T14720)
        #14749 (typecheck/should_compile/T14749)
      
      Sadly, this patch negatively affects performance of type-family-
      heavy code. The following patch fixes these performance degradations.
      However, the performance fixes are somewhat invasive and so I've
      kept them as a separate patch, labeling this one as [skip ci] so
      that validation doesn't fail on the performance cases.
      e3dbb44f
  34. 25 Mar, 2018 1 commit
    • Alec Theriault's avatar
      Support adding objects from TH · ceb91477
      Alec Theriault authored
      The user facing TH interface changes are:
      
        * 'addForeignFile' is renamed to 'addForeignSource'
        * 'qAddForeignFile'/'addForeignFile' now expect 'FilePath's
        * 'RawObject' is now a constructor for 'ForeignSrcLang'
        * 'qAddTempFile'/'addTempFile' let you request a temporary file
          from the compiler.
      
      Test Plan: unsure about this, added a TH test
      
      Reviewers: goldfire, bgamari, angerman
      
      Reviewed By: bgamari, angerman
      
      Subscribers: hsyl20, mboes, carter, simonmar, bitonic, ljli, rwbarton, thomie
      
      GHC Trac Issues: #14298
      
      Differential Revision: https://phabricator.haskell.org/D4217
      ceb91477
  35. 23 Mar, 2018 1 commit
    • Ryan Scott's avatar
      Allow PartialTypeSignatures in standalone deriving contexts · affdea82
      Ryan Scott authored
      Summary:
      At its core, this patch is a simple tweak that allows a user
      to write:
      
      ```lang=haskell
      deriving instance _ => Eq (Foo a)
      ```
      
      Which is functionally equivalent to:
      
      ```lang=haskell
      data Foo a = ...
        deriving Eq
      ```
      
      But with the added flexibility that `StandaloneDeriving` gives you
      (namely, the ability to use it anywhere, not just in the same module
      that `Foo` was declared in). This fixes #13324, and should hopefully
      address a use case brought up in #10607.
      
      Currently, only the use of a single, extra-constraints wildcard is
      permitted in a standalone deriving declaration. Any other wildcard
      is rejected, so things like
      `deriving instance (Eq a, _) => Eq (Foo a)` are currently forbidden.
      
      There are quite a few knock-on changes brought on by this change:
      
      * The `HsSyn` type used to represent standalone-derived instances
        was previously `LHsSigType`, which isn't sufficient to hold
        wildcard types. This needed to be changed to `LHsSigWcType` as a
        result.
      
      * Previously, `DerivContext` was a simple type synonym for
        `Maybe ThetaType`, under the assumption that you'd only ever be in
        the `Nothing` case if you were in a `deriving` clause. After this
        patch, that assumption no longer holds true, as you can also be
        in this situation with standalone deriving when an
        extra-constraints wildcard is used.
      
        As a result, I changed `DerivContext` to be a proper datatype that
        reflects the new wrinkle that this patch adds, and plumbed this
        through the relevant parts of `TcDeriv` and friends.
      
      * Relatedly, the error-reporting machinery in `TcErrors` also assumed
        that if you have any unsolved constraints in a derived instance,
        then you should be able to fix it by switching over to standalone
        deriving. This was always sound advice before, but with this new
        feature, it's possible to have unsolved constraints even when
        you're standalone-deriving something!
      
        To rectify this, I tweaked some constructors of `CtOrigin` a bit
        to reflect this new subtlety.
      
      This requires updating the Haddock submodule. See my fork at
      https://github.com/RyanGlScott/haddock/commit/067d52fd4be15a1842cbb05f42d9d482de0ad3a7
      
      Test Plan: ./validate
      
      Reviewers: simonpj, goldfire, bgamari
      
      Reviewed By: simonpj
      
      Subscribers: goldfire, rwbarton, thomie, mpickering, carter
      
      GHC Trac Issues: #13324
      
      Differential Revision: https://phabricator.haskell.org/D4383
      affdea82