1. 14 Jul, 2018 1 commit
    • Simon Peyton Jones's avatar
      Fix decompsePiCos and visible type application · 5b10d537
      Simon Peyton Jones authored
      Trac #15343 was caused by two things
      
      First, in TcHsType.tcHsTypeApp, which deals with the type argment
      in visible type application, we were failing to call
      solveLocalEqualities. But the type argument is like a user type
      signature so it's at least inconsitent not to do so.
      
      I thought that would nail it.  But it didn't. It turned out that we
      were ended up calling decomposePiCos on a type looking like this
          (f |> co) Int
      
      where co :: (forall a. ty) ~ (t1 -> t2)
      
      Now, 'co' is insoluble, and we'll report that later.  But meanwhile
      we don't want to crash in decomposePiCos.
      
      My fix involves keeping track of the type on both sides of the
      coercion, and ensuring that the outer shape matches before
      decomposing.  I wish there was a simpler way to do this. But
      I think this one is at least robust.
      
      I suppose it is possible that the decomposePiCos fix would
      have cured the original report, but I'm leaving the one-line
      tcHsTypeApp fix in too because it just seems more consistent.
      
      (cherry picked from commit aedbf7f1)
      5b10d537
  2. 12 Jul, 2018 1 commit
    • Ryan Scott's avatar
      Fix #15308 by suppressing invisble args more rigorously · 9bcbb222
      Ryan Scott authored
      Summary:
      There was a buglet in `stripInvisArgs` (which is part of the
      pretty-printing pipeline for types) in which only invisble arguments
      which came before any visible arguments would be suppressed, but any
      invisble arguments that came //after// visible ones would still be
      printed, even if `-fprint-explicit-kinds`  wasn't enabled.
      The fix is simple: make `stripInvisArgs` recursively process the
      remaining types even after a visible argument is encountered.
      
      Test Plan: make test TEST=T15308
      
      Reviewers: goldfire, bgamari
      
      Reviewed By: bgamari
      
      Subscribers: simonpj, rwbarton, thomie, carter
      
      GHC Trac Issues: #15308
      
      Differential Revision: https://phabricator.haskell.org/D4891
      
      (cherry picked from commit 93b7ac8d)
      9bcbb222
  3. 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
  4. 15 Jun, 2018 1 commit
    • Simon Peyton Jones's avatar
      Make better "fake tycons" in error recovery · 2f6069cc
      Simon Peyton Jones authored
      Consider (Trac #15215)
        data T a = MkT ...
        data S a = ...T...MkT....
      
      If there is an error in the definition of 'T' we add a
      "fake type constructor" to the type environment, so that we
      can continue to typecheck 'S'.  But we /were not/ adding
      a fake anything for 'MkT' and so there was an internal
      error when we met 'MkT' in the body of 'S'.
      
      The fix is to add fake tycons for all the 'implicits' of 'T'.
      This is done by mk_fake_tc in TcTyClsDecls.checkValidTyCl,
      which now returns a /list/ of TyCons rather than just one.
      
      On the way I did some refactoring:
      
      * Rename TcTyDecls.tcAddImplicits to tcAddTyConsToGblEnv
        and make it /include/ the TyCons themeselves as well
        as their implicits
      
      * Some incidental refactoring about tcRecSelBinds. The main
        thing is that I've avoided creating a HsValBinds that we
        immediately decompose.  That meant moving some deck chairs
        around.
      
      NB: The new error message for the regression test T15215
      has the opaque error "Illegal constraint in a type:", flagged
      in Trac #14845.  But that's the fault of the latter ticket.
      The fix here not to blame.
      2f6069cc
  5. 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
  6. 01 Apr, 2018 1 commit
    • 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
  7. 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
  8. 28 Jul, 2017 1 commit
    • Ryan Scott's avatar
      Add regression tests for #13601, #13780, #13877 · 424ecadb
      Ryan Scott authored
      Summary:
      Some recent commits happened to fix other issues:
      
      * c2417b87 fixed #13601 and #13780
      * 8e15e3d3 fixed the original program in #13877
      
      Let's add regression tests for each of these to ensure they stay fixed.
      
      Test Plan: make test TEST="T13601 T13780a T13780c T13877"
      
      Reviewers: goldfire, bgamari, austin
      
      Reviewed By: bgamari
      
      Subscribers: rwbarton, thomie
      
      GHC Trac Issues: #13601, #13780, #13877
      
      Differential Revision: https://phabricator.haskell.org/D3794
      424ecadb
  9. 27 Jul, 2017 1 commit
    • Richard Eisenberg's avatar
      Improve error messages around kind mismatches. · 8e15e3d3
      Richard Eisenberg authored
      Previously, when canonicalizing (or unifying, in uType) a
      heterogeneous equality, we emitted a kind equality and used the
      resulting coercion to cast one side of the heterogeneous equality.
      
      While sound, this led to terrible error messages. (See the bugs
      listed below.) The problem is that using the coercion built from
      the emitted kind equality is a bit like a wanted rewriting a wanted.
      The solution is to keep heterogeneous equalities as irreducible.
      
      See Note [Equalities with incompatible kinds] in TcCanonical.
      
      This commit also removes a highly suspicious switch to FM_SubstOnly
      when flattening in the kinds of a type variable. I have no idea
      why this was there, other than as a holdover from pre-TypeInType.
      I've not left a Note because there is simply no reason I can conceive
      of that the FM_SubstOnly should be there.
      
      One challenge with this patch is that the emitted derived equalities
      might get emitted several times: when a heterogeneous equality is
      in an implication and then gets floated out from the implication,
      the Derived is present both in and out of the implication. This
      causes a duplicate error message. (Test case:
      typecheck/should_fail/T7368) Solution: track the provenance of
      Derived constraints and refuse to float out a constraint that has
      an insoluble Derived.
      
      Lastly, this labels one test (dependent/should_fail/RAE_T32a)
      as expect_broken, because the problem is really #12919. The
      different handling of constraints in this patch exposes the error.
      
      This fixes bugs #11198, #12373, #13530, and #13610.
      
      test cases:
      typecheck/should_fail/{T8262,T8603,tcail122,T12373,T13530,T13610}
      8e15e3d3
  10. 23 Jan, 2017 1 commit
    • Simon Peyton Jones's avatar
      Apply the right substitution in ty-fam improvement · 2b64e926
      Simon Peyton Jones authored
      Trac #13135 showed that we were failing to apply the
      correct substitution to the un-substituted tyvars during
      type-family improvement using injectivity.  Specifically
      in TcInteractlinjImproveEqns we need to use instFlexiX.
      
      An outright bug, easy to fix.
      
      Slight refactoring along the way.  The quantified tyars of the axiom are
      readily to hand; we don't need to take the free tyvars of the LHS
      2b64e926
  11. 24 Oct, 2016 2 commits
  12. 21 Mar, 2016 1 commit
  13. 16 Mar, 2016 2 commits
    • eir@cis.upenn.edu's avatar
      Clean up some pretty-printing in errors. · 5d98b8bf
      eir@cis.upenn.edu authored
      It turns out that there were some pretty egregious mistakes
      in the code that suggested -fprint-explicit-kinds, which are
      fixed. This commit also reorders a bunch of error messages,
      which I think is an improvement.
      
      This also adds the test case for #11471, which is what
      triggered the cleanup in TcErrors. Now that #11473 is done,
      there is nothing more outstanding for #11471.
      
      test case: dependent/should_fail/T11471
      5d98b8bf
    • eir@cis.upenn.edu's avatar
      Fix #11473. · aade1112
      eir@cis.upenn.edu authored
      I've added a check in the zonker for representation polymorphism.
      I don't like having this be in the zonker, but I don't know where
      else to put it. It can't go in TcValidity, because a clever enough
      user could convince the solver to do bogus representation polymorphism
      even though there's nothing obviously wrong in what they wrote.
      Note that TcValidity doesn't run over *expressions*, which is where
      this problem arises.
      
      In any case, the check is simple and it works.
      
      test case: dependent/should_fail/T11473
      aade1112
  14. 15 Mar, 2016 3 commits
    • eir@cis.upenn.edu's avatar
      Fix #11648. · 55577a91
      eir@cis.upenn.edu authored
      We now check that a CUSK is really a CUSK and issue an error if
      it isn't. This also involves more solving and zonking in
      kcHsTyVarBndrs, which was the outright bug reported in #11648.
      
      Test cases: polykinds/T11648{,b}
      
      This updates the haddock submodule.
      
      [skip ci]
      55577a91
    • eir@cis.upenn.edu's avatar
      Fix #11334. · 84c773e1
      eir@cis.upenn.edu authored
      Now we fail when trying to default non-*-kinded kind variables
      with -XNoPolyKinds.
      
      test case: dependent/should_fail/T11334
      
      [skip ci]
      84c773e1
    • eir@cis.upenn.edu's avatar
      Fix #11407. · e9bf7bb5
      eir@cis.upenn.edu authored
      This removes the `defer_me` check that was in checkTauTvUpdate
      and uses only a type family check instead. The old defer_me check
      repeated work done by fast_check in occurCheckExpand.
      
      There is also some error message improvement, necessitated by
      the terrible error message that the test case produced, even when
      it didn't consume all of memory.
      
      test case: dependent/should_fail/T11407
      
      [skip ci]
      e9bf7bb5
  15. 14 Dec, 2015 1 commit
    • eir@cis.upenn.edu's avatar
      Suggest import Data.Kinds when * is out of scope · 023f11f5
      eir@cis.upenn.edu authored
      With -XTypeInType, `*` must be imported to be used. This patch makes
      sure the user knows this.
      
      But I'm not sure this is the best way to deal with `*`. Feedback welcome
      on either this small fix or the approach to `*`, in general.
      
      You may wish to see `Note [HsAppsTy]` in HsTypes if you want to take a
      broader view.
      
      Test Plan: dependent/should_fail/RenamingStar
      
      Reviewers: simonpj, bgamari, austin
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1610
      023f11f5
  16. 11 Dec, 2015 1 commit
    • eir@cis.upenn.edu's avatar
      Add kind equalities to GHC. · 67465497
      eir@cis.upenn.edu authored
      This implements the ideas originally put forward in
      "System FC with Explicit Kind Equality" (ICFP'13).
      
      There are several noteworthy changes with this patch:
       * We now have casts in types. These change the kind
         of a type. See new constructor `CastTy`.
      
       * All types and all constructors can be promoted.
         This includes GADT constructors. GADT pattern matches
         take place in type family equations. In Core,
         types can now be applied to coercions via the
         `CoercionTy` constructor.
      
       * Coercions can now be heterogeneous, relating types
         of different kinds. A coercion proving `t1 :: k1 ~ t2 :: k2`
         proves both that `t1` and `t2` are the same and also that
         `k1` and `k2` are the same.
      
       * The `Coercion` type has been significantly enhanced.
         The documentation in `docs/core-spec/core-spec.pdf` reflects
         the new reality.
      
       * The type of `*` is now `*`. No more `BOX`.
      
       * Users can write explicit kind variables in their code,
         anywhere they can write type variables. For backward compatibility,
         automatic inference of kind-variable binding is still permitted.
      
       * The new extension `TypeInType` turns on the new user-facing
         features.
      
       * Type families and synonyms are now promoted to kinds. This causes
         trouble with parsing `*`, leading to the somewhat awkward new
         `HsAppsTy` constructor for `HsType`. This is dispatched with in
         the renamer, where the kind `*` can be told apart from a
         type-level multiplication operator. Without `-XTypeInType` the
         old behavior persists. With `-XTypeInType`, you need to import
         `Data.Kind` to get `*`, also known as `Type`.
      
       * The kind-checking algorithms in TcHsType have been significantly
         rewritten to allow for enhanced kinds.
      
       * The new features are still quite experimental and may be in flux.
      
       * TODO: Several open tickets: #11195, #11196, #11197, #11198, #11203.
      
       * TODO: Update user manual.
      
      Tickets addressed: #9017, #9173, #7961, #10524, #8566, #11142.
      Updates Haddock submodule.
      67465497