1. 07 Jan, 2016 4 commits
    • Gabor Greif's avatar
      Typos in docs and comments · c78fedde
      Gabor Greif authored
      c78fedde
    • Simon Peyton Jones's avatar
      Turn AThing into ATcTyCon, in TcTyThing · a5cea73c
      Simon Peyton Jones authored
      This change tidies up and simplifies (a bit) the knot-tying
      when kind-checking groups of type and class declarations.
      
      The trouble (shown by Trac #11356) was that we wanted an error message
      (a kind-mismatch) that involved a type mentioned a (AThing k), which
      blew up.
      
      Since we now seem to have TcTyCons, I decided to use them here.
      It's still not great, but it's easier to understand and more robust.
      a5cea73c
    • Simon Peyton Jones's avatar
      Use an Implication in 'deriving' error · 02c1c573
      Simon Peyton Jones authored
      Trac #11437 showed that erroneous constraints from a 'deriving'
      clause need to be wrapped in an Implication to properly scope
      their skolems.
      
      The main change is in TcDeriv.simplifyDeriv; the call to
      buildImplicationFor is new.
      02c1c573
    • Simon Peyton Jones's avatar
      Tidy up tidySkolemInfo · 290a553e
      Simon Peyton Jones authored
      Previously tidySkolemInfo used tidyOpenType, and returned a new
      TidyEnv.  But that's not needed any more, because all the skolems
      should be in scope in the constraint tree.
      
      I also removed a (now-unnecessary) field of UnifyForAllSkol
      290a553e
  2. 05 Jan, 2016 1 commit
    • Joachim Breitner's avatar
      Add (failing) test case for #11347 · 1a8b752d
      Joachim Breitner authored
      Unfortunately, I could not add the expected error message, so if someone
      accidentally fixes this bug, this test will still be failing (no harm).
      But maybe someone stumbles over it then and can update the expected
      output.
      1a8b752d
  3. 01 Jan, 2016 1 commit
    • Simon Peyton Jones's avatar
      Add strictness for runRW# · f3cc3456
      Simon Peyton Jones authored
      runRW# isn't inlined until CorePrep, so it's good to expose its
      strictness.  Moreover, if we don't we can get obscure failures
      in coreToStg; see Note [runRW arg] in CorePrep.
      
      This fixes Trac #11291, and makes DfltProb1 compile with -O
      always in order to expose it more vigorously
      f3cc3456
  4. 30 Dec, 2015 1 commit
    • eir@cis.upenn.edu's avatar
      Fix #11305. · c06b46d0
      eir@cis.upenn.edu authored
      Summary:
      In the fallthrough case when doing a subsumption case, we
      need to deeply instantiate to remove any buried foralls in
      the "actual" type.
      
      Once this validates, please feel free to commit it; I may not
      have the chance to do this on Tuesday. Back in full action on
      Wed.
      
      Test Plan: ./validate, typecheck/should_compiler/T11305
      
      Reviewers: austin, bgamari, hvr
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1715
      
      GHC Trac Issues: #11305
      c06b46d0
  5. 26 Dec, 2015 3 commits
  6. 24 Dec, 2015 1 commit
    • eir@cis.upenn.edu's avatar
      Visible type application · 2db18b81
      eir@cis.upenn.edu authored
      This re-working of the typechecker algorithm is based on
      the paper "Visible type application", by Richard Eisenberg,
      Stephanie Weirich, and Hamidhasan Ahmed, to be published at
      ESOP'16.
      
      This patch introduces -XTypeApplications, which allows users
      to say, for example `id @Int`, which has type `Int -> Int`. See
      the changes to the user manual for details.
      
      This patch addresses tickets #10619, #5296, #10589.
      2db18b81
  7. 23 Dec, 2015 3 commits
    • Jan Stolarek's avatar
      Test #10432 · f141f416
      Jan Stolarek authored
      Summary: A regression test for #10432, which seems to already be fixed.
      
      Test Plan: ./validate
      
      Reviewers: simonpj, austin, bgamari
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1691
      
      GHC Trac Issues: #10432
      f141f416
    • Eric Seidel's avatar
      Allow CallStacks to be frozen · 380b25ea
      Eric Seidel authored
      This introduces "freezing," an operation which prevents further
      locations from being appended to a CallStack.  Library authors may want
      to prevent CallStacks from exposing implementation details, as a matter
      of hygiene. For example, in
      
      ```
      head [] = error "head: empty list"
      
      ghci> head []
      *** Exception: head: empty list
      CallStack (from implicit params):
        error, called at ...
      ```
      
      including the call-site of `error` in `head` is not strictly necessary
      as the error message already specifies clearly where the error came
      from.
      
      So we add a function `freezeCallStack` that wraps an existing CallStack,
      preventing further call-sites from being pushed onto it. In other words,
      
      ```
      pushCallStack callSite (freezeCallStack callStack) = freezeCallStack callStack
      ```
      
      Now we can define `head` to not produce a CallStack at all
      
      ```
      head [] =
        let ?callStack = freezeCallStack emptyCallStack
        in error "head: empty list"
      
      ghci> head []
      *** Exception: head: empty list
      CallStack (from implicit params):
        error, called at ...
      ```
      
      ---
      
      1. We add the `freezeCallStack` and `emptyCallStack` and update the
         definition of `CallStack` to support this functionality.
      
      2. We add `errorWithoutStackTrace`, a variant of `error` that does not
         produce a stack trace, using this feature. I think this is a sensible
         wrapper function to provide in case users want it.
      
      3. We replace uses of `error` in base with `errorWithoutStackTrace`. The
         rationale is that base does not export any functions that use CallStacks
         (except for `error` and `undefined`) so there's no way for the stack
         traces (from Implicit CallStacks) to include user-defined functions.
         They'll only contain the call to `error` itself. As base already has a
         good habit of providing useful error messages that name the triggering
         function, the stack trace really just adds noise to the error. (I don't
         have a strong opinion on whether we should include this third commit,
         but the change was very mechanical so I thought I'd include it anyway in
         case there's interest)
      
      4. Updates tests in `array` and `stm` submodules
      
      Test Plan: ./validate, new test is T11049
      
      Reviewers: simonpj, nomeata, goldfire, austin, hvr, bgamari
      
      Reviewed By: simonpj
      
      Subscribers: thomie
      
      Projects: #ghc
      
      Differential Revision: https://phabricator.haskell.org/D1628
      
      GHC Trac Issues: #11049
      380b25ea
    • Simon Peyton Jones's avatar
      Test Trac #11274 · ed213ead
      Simon Peyton Jones authored
      ed213ead
  8. 21 Dec, 2015 3 commits
  9. 18 Dec, 2015 1 commit
    • Simon Peyton Jones's avatar
      tcCheckSatisfiability: less aggressive superclass expansion · ff752a1a
      Simon Peyton Jones authored
      In the pattern-match check we are looking for a proof of
      *unsatisfiablity* among a bunch of givens.  The unsat-ness might be
      hidden in the superclasses, so we must expand them.  But in the common
      case where the constraints are satisfiable, we don't want to expand
      a recursive superclass forever.
      
      This is all a bit arbitrary, but then the whole question is
      undecidable anyway.
      
      The bug in Trac #10592 comment:12 was that I expanded superclasses
      forever.  This patch fixes it.
      ff752a1a
  10. 17 Dec, 2015 2 commits
    • eir@cis.upenn.edu's avatar
      Fix #11230. · 1722fa10
      eir@cis.upenn.edu authored
      Previously, we were optimizing away all case expressions over
      coercions with dead binders. But sometimes we want to force
      the coercion expression. Like when it contains an error.
      
      Test case: typecheck/should_run/T11230
      1722fa10
    • quchen's avatar
      Conditionally show plural "s" in warnings · 4f870f84
      quchen authored
      Redundant constraints and defaulting warnings had "constraint(s)" in
      their messages; the "s" is now conditional based on the number of things
      warned about.
      
      Reviewers: hvr, austin, bgamari
      
      Reviewed By: bgamari
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1647
      4f870f84
  11. 16 Dec, 2015 1 commit
  12. 15 Dec, 2015 2 commits
    • Ben Gamari's avatar
      Narrow scope of special-case for unqualified printing of names in core libraries · e2c91738
      Ben Gamari authored
      Commit 547c5971 modifies the
      pretty-printer to render names from a set of core packages (`base`,
      `ghc-prim`, `template-haskell`) as unqualified. The idea here was that
      many of these names typically are not in scope but are well-known by the
      user and therefore qualification merely introduces noise.
      
      This, however, is a very large hammer and potentially breaks any
      consumer who relies on parsing GHC output (hence #11208). This commit
      partially reverts this change, now only printing `Constraint` (which
      appears quite often in errors) as unqualified.
      
      Fixes #11208.
      
      Updates tests in `array` submodule.
      
      Test Plan: validate
      
      Reviewers: hvr, thomie, austin
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1619
      
      GHC Trac Issues: #11208
      e2c91738
    • Simon Peyton Jones's avatar
      Allow recursive (undecidable) superclasses · 6eabb6dd
      Simon Peyton Jones authored
      This patch fulfils the request in Trac #11067, #10318, and #10592,
      by lifting the conservative restrictions on superclass constraints.
      
      These restrictions are there (and have been since Haskell was born) to
      ensure that the transitive superclasses of a class constraint is a finite
      set.  However (a) this restriction is conservative, and can be annoying
      when there really is no recursion, and (b) sometimes genuinely recursive
      superclasses are useful (see the tickets).
      
      Dimitrios and I worked out that there is actually a relatively simple way
      to do the job. It’s described in some detail in
      
         Note [The superclass story] in TcCanonical
         Note [Expanding superclasses] in TcType
      
      In brief, the idea is to expand superclasses only finitely, but to
      iterate (using a loop that already existed) if there are more
      superclasses to explore.
      
      Other small things
      
      - I improved grouping of error messages a bit in TcErrors
      
      - I re-centred the haddock.compiler test, which was at 9.8%
        above the norm, and which this patch pushed slightly over
      6eabb6dd
  13. 12 Dec, 2015 1 commit
    • Eric Seidel's avatar
      Rework the Implicit CallStack solver to handle local lets. · 3ec8288a
      Eric Seidel authored
      We can't just solve CallStack constraints indiscriminately when they
      occur in the RHS of a let-binder. The top-level given CallStack (if
      any) will not be in scope, so I've re-worked the CallStack solver as
      follows:
      
      1. CallStacks are treated like regular IPs unless one of the following
         two rules apply.
      
      2. In a function call, we push the call-site onto a NEW wanted
         CallStack, which GHC will solve as a regular IP (either directly from a
         given, or by quantifying over it in a local let).
      
      3. If, after the constraint solver is done, any wanted CallStacks
         remain, we default them to the empty CallStack. This rule exists mainly
         to clean up after rule 2 in a top-level binder with no given CallStack.
      
      In rule (2) we have to be careful to emit the new wanted with an
      IPOccOrigin instead of an OccurrenceOf origin, so rule (2) doesn't fire
      again. This is a bit shady but I've updated the Note to explain the
      trick.
      
      Test Plan: validate
      
      Reviewers: simonpj, austin, bgamari, hvr
      
      Reviewed By: simonpj, bgamari
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1422
      
      GHC Trac Issues: #10845
      3ec8288a
  14. 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
  15. 09 Dec, 2015 1 commit
  16. 08 Dec, 2015 1 commit
  17. 04 Dec, 2015 1 commit
    • Simon Peyton Jones's avatar
      Tidy user type errors in checkValidType · 67565a72
      Simon Peyton Jones authored
      Trac #11144 showed that we need to tidy the type in the error message
      generated in TcValidity.checkUserTypeError.
      
      This is still unsatisfactory.  checkValidType was originally supposed
      to be called only on types gotten directly from user-written HsTypes.
      So its error messages do no tidying.  But TcBinds calls it checkValidType
      on an /inferred/ type, which may need tidying.
      
      Still this at least fixes the bad error message in CustomTypeErrors02,
      which was the original ticket.
      
      Some other small refactorings:
      
      * Remove unused Kind result of getUserTypeErrorMsg
      * Rename isUserErrorTy  -->   userTypeError_maybe
      67565a72
  18. 03 Dec, 2015 1 commit
    • Georgios Karachalias's avatar
      Major Overhaul of Pattern Match Checking (Fixes #595) · 8a506104
      Georgios Karachalias authored
      This patch adresses several problems concerned with exhaustiveness and
      redundancy checking of pattern matching. The list of improvements includes:
      
      * Making the check type-aware (handles GADTs, Type Families, DataKinds, etc.).
        This fixes #4139, #3927, #8970 and other related tickets.
      
      * Making the check laziness-aware. Cases that are overlapped but affect
        evaluation are issued now with "Patterns have inaccessible right hand side".
        Additionally, "Patterns are overlapped" is now replaced by "Patterns are
        redundant".
      
      * Improved messages for literals. This addresses tickets #5724, #2204, etc.
      
      * Improved reasoning concerning cases where simple and overloaded
        patterns are matched (See #322).
      
      * Substantially improved reasoning for pattern guards. Addresses #3078.
      
      * OverloadedLists extension does not break exhaustiveness checking anymore
        (addresses #9951). Note that in general this cannot be handled but if we know
        that an argument has type '[a]', we treat it as a list since, the instance of
        'IsList' gives the identity for both 'fromList' and 'toList'. If the type is
        not clear or is not the list type, then the check cannot do much still. I am
        a bit concerned about OverlappingInstances though, since one may override the
        '[a]' instance with e.g. an '[Int]' instance that is not the identity.
      
      * Improved reasoning for nested pattern matching (partial solution). Now we
        propagate type and (some) term constraints deeper when checking, so we can
        detect more inconsistencies. For example, this is needed for #4139.
      
      I am still not satisfied with several things but I would like to address at
      least the following before the next release:
          Term constraints are too many and not printed for non-exhaustive matches
      (with the exception of literals). This sometimes results in two identical (in
      appearance) uncovered warnings. Unless we actually show their difference, I
      would like to have a single warning.
      8a506104
  19. 01 Dec, 2015 1 commit
    • Simon Peyton Jones's avatar
      Refactor treatment of wildcards · 1e041b73
      Simon Peyton Jones authored
      This patch began as a modest refactoring of HsType and friends, to
      clarify and tidy up exactly where quantification takes place in types.
      Although initially driven by making the implementation of wildcards more
      tidy (and fixing a number of bugs), I gradually got drawn into a pretty
      big process, which I've been doing on and off for quite a long time.
      
      There is one compiler performance regression as a result of all
      this, in perf/compiler/T3064.  I still need to look into that.
      
      * The principal driving change is described in Note [HsType binders]
        in HsType.  Well worth reading!
      
      * Those data type changes drive almost everything else.  In particular
        we now statically know where
      
             (a) implicit quantification only (LHsSigType),
                 e.g. in instance declaratios and SPECIALISE signatures
      
             (b) implicit quantification and wildcards (LHsSigWcType)
                 can appear, e.g. in function type signatures
      
      * As part of this change, HsForAllTy is (a) simplified (no wildcards)
        and (b) split into HsForAllTy and HsQualTy.  The two contructors
        appear when and only when the correponding user-level construct
        appears.  Again see Note [HsType binders].
      
        HsExplicitFlag disappears altogether.
      
      * Other simplifications
      
           - ExprWithTySig no longer needs an ExprWithTySigOut variant
      
           - TypeSig no longer needs a PostRn name [name] field
             for wildcards
      
           - PatSynSig records a LHsSigType rather than the decomposed
             pieces
      
           - The mysterious 'GenericSig' is now 'ClassOpSig'
      
      * Renamed LHsTyVarBndrs to LHsQTyVars
      
      * There are some uninteresting knock-on changes in Haddock,
        because of the HsSyn changes
      
      I also did a bunch of loosely-related changes:
      
      * We already had type synonyms CoercionN/CoercionR for nominal and
        representational coercions.  I've added similar treatment for
      
            TcCoercionN/TcCoercionR
      
            mkWpCastN/mkWpCastN
      
        All just type synonyms but jolly useful.
      
      * I record-ised ForeignImport and ForeignExport
      
      * I improved the (poor) fix to Trac #10896, by making
        TcTyClsDecls.checkValidTyCl recover from errors, but adding a
        harmless, abstract TyCon to the envt if so.
      
      * I did some significant refactoring in RnEnv.lookupSubBndrOcc,
        for reasons that I have (embarrassingly) now totally forgotten.
        It had to do with something to do with import and export
      
      Updates haddock submodule.
      1e041b73
  20. 29 Nov, 2015 1 commit
    • quchen's avatar
      Implement warnings for Semigroups as parent of Monoid · 290def72
      quchen authored
      This patch is similar to the AMP patch (#8004), which offered two
      functions:
      
        1. Warn when an instance of a class has been given, but the type does
           not have a certain superclass instance
        2. Warn when top-level definitions conflict with future Prelude names
      
      These warnings are issued as part of the new `-Wcompat` warning group.
      
      Reviewers: hvr, ekmett, austin, bgamari
      
      Reviewed By: hvr, ekmett, bgamari
      
      Subscribers: ekmett, thomie
      
      Differential Revision: https://phabricator.haskell.org/D1539
      
      GHC Trac Issues: #11139
      290def72
  21. 25 Nov, 2015 1 commit
    • Simon Peyton Jones's avatar
      Refactor default methods (Trac #11105) · 924f8517
      Simon Peyton Jones authored
      This patch does some signficant refactoring to the treatment
      of default methods in class declarations, and more generally
      to the type checking of type/class decls.
      
      Highlights:
      
      * When the class has a generic-default method, such as
           class C a where
             op :: a -> a -> Bool
             default op :: Ord a => a -> a -> a
        the ClassOpItem records the type of the generic-default,
        in this case the type (Ord a => a -> a -> a)
      
      * I killed off Class.DefMeth in favour of the very-similar
        BasicTypes.DefMethSpec.  However it turned out to be better
        to use a Maybe, thus
            Maybe (DefMethSpec Type)
        with Nothing meaning "no default method".
      
      * In TcTyClsDecls.tcTyClGroup, we used to accumulate a [TyThing],
        but I found a way to make it much simpler, accumulating only
        a [TyCon].  Much less wrapping and unwrapping.
      
      * On the way I also fixed Trac #10896 in a better way. Instead
        of killing off all ambiguity checks whenever there are any type
        errors (the fix in commit 8e8b9ed9), I instead recover in
        TcTyClsDecls.checkValidTyCl.
      
      There was a lot of associated simplification all round
      924f8517
  22. 24 Nov, 2015 2 commits
    • elaforge's avatar
      Rearrange error msgs and add section markers (Trac #11014). · c05fddde
      elaforge authored
      This puts the "Relevant bindings" section at the end.
      
      It uses a TcErrors.Report Monoid to divide messages by importance and
      then mappends them together.  This is not the most efficient way since
      there are various intermediate Reports and list appends, but it probably
      doesn't matter since error messages shouldn't get that large, and are
      usually prepended.  In practice, everything is `important` except
      `relevantBindings`, which is `supplementary`.
      
      ErrMsg's errMsgShortDoc and errMsgExtraInfo were extracted into ErrDoc,
      which has important, context, and suppelementary fields.  Each of those
      three sections is marked with a bullet character, '•' on unicode
      terminals and '*' on ascii terminals.  Since this breaks tons of tests,
      I also modified testlib.normalise_errmsg to strip out '•'s.
      
      --- Additional notes:
      
      To avoid prepending * to an empty doc, I needed to filter empty docs.
      This seemed less error-prone than trying to modify everyone who produces
      SDoc to instead produce Maybe SDoc.  So I added `Outputable.isEmpty`.
      Unfortunately it needs a DynFlags, which is kind of bogus, but otherwise
      I think I'd need another Empty case for SDoc, and then it couldn't be a
      newtype any more.
      
      ErrMsg's errMsgShortString is only used by the Show instance, which is
      in turn only used by Show HscTypes.SourceError, which is in turn only
      needed for the Exception instance.  So it's probably possible to get rid
      of errMsgShortString, but that would a be an unrelated cleanup.
      
      Fixes #11014.
      
      Test Plan: see above
      
      Reviewers: austin, simonpj, thomie, bgamari
      
      Reviewed By: thomie, bgamari
      
      Subscribers: simonpj, nomeata, thomie
      
      Differential Revision: https://phabricator.haskell.org/D1427
      
      GHC Trac Issues: #11014
      c05fddde
    • Herbert Valerio Riedel's avatar
      Add `PrelNames.thenAName` for `Applicative(*>)` · 12dbc892
      Herbert Valerio Riedel authored
      This is needed to allow subsequent patches to refer to `*>`.
      
      While at it, this commit also groups together the `Applicative` definitions
      to reduce confusion.
      
      Reviewed By: austin
      
      Differential Revision: https://phabricator.haskell.org/D1513
      12dbc892
  23. 23 Nov, 2015 1 commit
  24. 18 Nov, 2015 1 commit
    • msosn's avatar
      Fix inconsistent pretty-printing of type families · c61759d5
      msosn authored
      After the changes, the three functions used to print type families
      were identical, so they are refactored into one.
      
      Original RHSs of data instance declarations are recreated and
      printed in user error messages.
      
      RHSs containing representation TyCons are printed in the
      Coercion Axioms section in a typechecker dump.
      
      Add vbar to the list of SDocs exported by Outputable.
      Replace all text "|" docs with it.
      
      Fixes #10839
      
      Reviewers: goldfire, jstolarek, austin, bgamari
      
      Reviewed By: jstolarek
      
      Subscribers: jstolarek, thomie
      
      Differential Revision: https://phabricator.haskell.org/D1441
      
      GHC Trac Issues: #10839
      c61759d5
  25. 16 Nov, 2015 2 commits
  26. 14 Nov, 2015 1 commit
  27. 13 Nov, 2015 1 commit
    • Simon Marlow's avatar
      Make 'error' include the CCS call stack when profiled · 8988be85
      Simon Marlow authored
      Summary:
      The idea here is that this gives a more detailed stack trace in two
      cases:
      
      1. With `-prof` and `-fprof-auto`
      2. In GHCi (see #11047)
      
      Example, with an error inserted in nofib/shootout/binary-trees:
      
      ```
      $ ./Main 3
      Main: z
      CallStack (from ImplicitParams):
        error, called at Main.hs:67:29 in main:Main
      CallStack (from -prof):
        Main.check' (Main.hs:(67,1)-(68,82))
        Main.check (Main.hs:63:1-21)
        Main.stretch (Main.hs:32:35-57)
        Main.main.c (Main.hs:32:9-57)
        Main.main (Main.hs:(27,1)-(43,42))
        Main.CAF (<entire-module>)
      ```
      
      This doesn't quite obsolete +RTS -xc, which also attempts to display
      more information in the case when the error is in a CAF, but I'm
      exploring other solutions to that.
      
      Includes submodule updates.
      
      Test Plan: validate
      
      Reviewers: simonpj, ezyang, gridaphobe, bgamari, hvr, austin
      
      Reviewed By: bgamari
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1426
      8988be85