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This exposes `template-haskell` functions for querying the language
extensions which are enabled when compiling a module,

- an `isExtEnabled` function to check whether an extension is enabled
- an `extsEnabled` function to obtain a full list of enabled extensions

To avoid code duplication this adds a `GHC.LanguageExtensions` module to
`ghc-boot` and moves `DynFlags.ExtensionFlag` into it. A happy
consequence of this is that the ungainly `DynFlags` lost around 500
lines. Moreover, flags corresponding to language extensions are now
clearly distinguished from other flags due to the `LangExt.*` prefix.

Updates haddock submodule.

This fixes #10820.

Test Plan: validate

Reviewers: austin, spinda, hvr, goldfire, alanz

Reviewed By: goldfire

Subscribers: mpickering, RyanGlScott, hvr, simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D1200

GHC Trac Issues: #10820

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.

Summary: Before, `PatSyn`s were getting added twice to `tcg_patsyns` so
when inspecting afterwards there were duplicates in the list.
This makes sure that only they only get added once.

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1597

See Trac #11176

Checking for missing signatures before renaming the export list is
prone to errors, so we now perform the check in `reportUnusedNames` at
which point everything has been renamed.

Test Plan: validate, new test case is T10908

Reviewers: goldfire, simonpj, austin, bgamari

Subscribers: thomie

Projects: #ghc

Differential Revision: https://phabricator.haskell.org/D1561

GHC Trac Issues: #10908

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

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.

At the moment the API Annotations can only be used on the ParsedSource,
as there are changes made to the RenamedSource that prevent it from
being used to round trip source code.

It is possible to build a map from every Located Name in the
RenamedSource from its location to the Name, which can then be used when
resolved names are required when changing the ParsedSource.

However, there are instances where the identifier is not located,
specifically

  (GHC.VarPat name)
  (GHC.HsVar name)
  (GHC.UserTyVar name)
  (GHC.HsTyVar name)

Replace each of the name types above with (Located name)

Updates the haddock submodule.

Test Plan: ./validate

Reviewers: austin, goldfire, bgamari

Reviewed By: bgamari

Subscribers: goldfire, thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D1512

GHC Trac Issues: #11019

Summary:
This reverts commit 06d46b1e.

This also has a Haddock submodule update.

Test Plan: validate

Reviewers: simonpj, austin, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1475

Add a new language extension `-XStrict` which turns all bindings strict
as if the programmer had written a `!` before it. This also upgrades
ordinary Haskell to allow recursive and polymorphic strict bindings.

See the wiki[1] and the Note [Desugar Strict binds] in DsBinds for
specification and implementation details.

[1] https://ghc.haskell.org/trac/ghc/wiki/StrictPragma

Reviewers: austin, tibbe, simonpj, bgamari

Reviewed By: tibbe, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1142

GHC Trac Issues: #8347

Summary:
At the moment ghc-exactprint, which uses the GHC API Annotations to
provide a framework for roundtripping Haskell source code with optional
AST edits, has to implement a horrible workaround to manage the points
where layout needs to be captured.

These are

    MatchGroup
    HsDo
    HsCmdDo
    HsLet
    LetStmt
    HsCmdLet
    GRHSs

To provide a more natural representation, the contents subject to layout
rules need to be wrapped in a SrcSpan.

This commit does this.

Trac ticket #10250

Test Plan: ./validate

Reviewers: hvr, goldfire, bgamari, austin, mpickering

Reviewed By: mpickering

Subscribers: thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D1370

GHC Trac Issues: #10250

One of the changes D538 introduced is to add `m_fun_id_infix` to `Match`

```lang=hs
data Match id body
  = Match {
        m_fun_id_infix :: (Maybe (Located id,Bool)),
          -- fun_id and fun_infix for functions with multiple equations
          -- only present for a RdrName. See note [fun_id in Match]
        m_pats :: [LPat id], -- The patterns
        m_type :: (Maybe (LHsType id)),
                                 -- A type signature for the result of the match
                                 -- Nothing after typechecking
        m_grhss :: (GRHSs id body)
  } deriving (Typeable)
```

This was done to track the individual locations and fixity of the
`fun_id` for each of the defining equations for a function when there
are more than one.

For example, the function `(&&&)` is defined with some prefix and some
infix equations below.

```lang=hs
    (&&&  ) [] [] =  []
    xs    &&&   [] =  xs
    (  &&&  ) [] ys =  ys
```

This means that the fun_infix is now superfluous in the `FunBind`. This
has not been removed as a potentially risky change just before 7.10 RC2,
and so must be done after.

This ticket captures that task, which includes processing these fields
through the renamer and beyond.

Ticket #9988 introduced these fields into `Match` through renaming, this
ticket it to continue through type checking and then remove it from
`FunBind` completely.

The split happened so that #9988 could land in 7.10

Trac ticket : #10061

Test Plan: ./validate

Reviewers: goldfire, austin, simonpj, bgamari

Reviewed By: bgamari

Subscribers: simonpj, thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D1285

GHC Trac Issues: #10061

This is the second attempt at merging D757.

This patch implements the idea floated in Trac #9858, namely that we
should generate type-representation information at the data type
declaration site, rather than when solving a Typeable constraint.

However, this turned out quite a bit harder than I expected. I still
think it's the right thing to do, and it's done now, but it was quite
a struggle.

See particularly

 * Note [Grand plan for Typeable] in TcTypeable (which is a new module)
 * Note [The overall promotion story] in DataCon (clarifies existing
stuff)

The most painful bit was that to generate Typeable instances (ie
TyConRepName bindings) for every TyCon is tricky for types in ghc-prim
etc:

 * We need to have enough data types around to *define* a TyCon
 * Many of these types are wired-in

Also, to minimise the code generated for each data type, I wanted to
generate pure data, not CAFs with unpackCString# stuff floating about.

Performance
~~~~~~~~~~~
Three perf/compiler tests start to allocate quite a bit more. This isn't
surprising, because they all allocate zillions of data types, with
practically no other code, esp. T1969

 * T1969:    GHC allocates 19% more
 * T4801:    GHC allocates 13% more
 * T5321FD:  GHC allocates 13% more
 * T9675:    GHC allocates 11% more
 * T783:     GHC allocates 11% more
 * T5642:    GHC allocates 10% more

I'm treating this as acceptable. The payoff comes in Typeable-heavy
code.

Remaining to do
~~~~~~~~~~~~~~~

 * I think that "TyCon" and "Module" are over-generic names to use for
   the runtime type representations used in GHC.Typeable. Better might
be
   "TrTyCon" and "TrModule". But I have not yet done this

 * Add more info the the "TyCon" e.g. source location where it was
   defined

 * Use the new "Module" type to help with Trac Trac #10068

 * It would be possible to generate TyConRepName (ie Typeable
   instances) selectively rather than all the time. We'd need to persist
   the information in interface files. Lacking a motivating reason I
have
   not done this, but it would not be difficult.

Refactoring
~~~~~~~~~~~
As is so often the case, I ended up refactoring more than I intended.
In particular

 * In TyCon, a type *family* (whether type or data) is repesented by a
   FamilyTyCon
     * a algebraic data type (including data/newtype instances) is
       represented by AlgTyCon This wasn't true before; a data family
       was represented as an AlgTyCon. There are some corresponding
       changes in IfaceSyn.

     * Also get rid of the (unhelpfully named) tyConParent.

 * In TyCon define 'Promoted', isomorphic to Maybe, used when things are
   optionally promoted; and use it elsewhere in GHC.

 * Cleanup handling of knownKeyNames

 * Each TyCon, including promoted TyCons, contains its TyConRepName, if
   it has one. This is, in effect, the name of its Typeable instance.

Updates haddock submodule

Test Plan: Let Harbormaster validate

Reviewers: austin, hvr, goldfire

Subscribers: goldfire, thomie

Differential Revision: https://phabricator.haskell.org/D1404

GHC Trac Issues: #9858

This reverts commit bef2f03e.

This merge was botched

Also reverts haddock submodule.

This patch implements the idea floated in Trac #9858, namely that we
should generate type-representation information at the data type
declaration site, rather than when solving a Typeable constraint.

However, this turned out quite a bit harder than I expected. I still
think it's the right thing to do, and it's done now, but it was quite
a struggle.

See particularly

 * Note [Grand plan for Typeable] in TcTypeable (which is a new module)
 * Note [The overall promotion story] in DataCon (clarifies existing stuff)

The most painful bit was that to generate Typeable instances (ie
TyConRepName bindings) for every TyCon is tricky for types in ghc-prim
etc:

 * We need to have enough data types around to *define* a TyCon
 * Many of these types are wired-in

Also, to minimise the code generated for each data type, I wanted to
generate pure data, not CAFs with unpackCString# stuff floating about.

Performance
~~~~~~~~~~~
Three perf/compiler tests start to allocate quite a bit more. This isn't
surprising, because they all allocate zillions of data types, with
practically no other code, esp. T1969

 * T3294:   GHC allocates 110% more (filed #11030 to track this)
 * T1969:   GHC allocates 30% more
 * T4801:   GHC allocates 14% more
 * T5321FD: GHC allocates 13% more
 * T783:    GHC allocates 12% more
 * T9675:   GHC allocates 12% more
 * T5642:   GHC allocates 10% more
 * T9961:   GHC allocates 6% more

 * T9203:   Program allocates 54% less

I'm treating this as acceptable. The payoff comes in Typeable-heavy
code.

Remaining to do
~~~~~~~~~~~~~~~

 * I think that "TyCon" and "Module" are over-generic names to use for
   the runtime type representations used in GHC.Typeable. Better might be
   "TrTyCon" and "TrModule". But I have not yet done this

 * Add more info the the "TyCon" e.g. source location where it was
   defined

 * Use the new "Module" type to help with Trac Trac #10068

 * It would be possible to generate TyConRepName (ie Typeable
   instances) selectively rather than all the time. We'd need to persist
   the information in interface files. Lacking a motivating reason I have
   not done this, but it would not be difficult.

Refactoring
~~~~~~~~~~~
As is so often the case, I ended up refactoring more than I intended.
In particular

 * In TyCon, a type *family* (whether type or data) is repesented by a
   FamilyTyCon
     * a algebraic data type (including data/newtype instances) is
       represented by AlgTyCon This wasn't true before; a data family
       was represented as an AlgTyCon. There are some corresponding
       changes in IfaceSyn.

     * Also get rid of the (unhelpfully named) tyConParent.

 * In TyCon define 'Promoted', isomorphic to Maybe, used when things are
   optionally promoted; and use it elsewhere in GHC.

 * Cleanup handling of knownKeyNames

 * Each TyCon, including promoted TyCons, contains its TyConRepName, if
   it has one. This is, in effect, the name of its Typeable instance.

Requires update of the haddock submodule.

Differential Revision: https://phabricator.haskell.org/D757

This patch implements an extension to pattern synonyms which allows user
to specify pattern synonyms using record syntax. Doing so generates
appropriate selectors and update functions.

=== Interaction with Duplicate Record Fields ===

The implementation given here isn't quite as general as it could be with
respect to the recently-introduced `DuplicateRecordFields` extension.

Consider the following module:

    {-# LANGUAGE DuplicateRecordFields #-}
    {-# LANGUAGE PatternSynonyms #-}

    module Main where

    pattern S{a, b} = (a, b)
    pattern T{a}    = Just a

    main = do
      print S{ a = "fst", b = "snd" }
      print T{ a = "a" }

In principle, this ought to work, because there is no ambiguity. But at
the moment it leads to a "multiple declarations of a" error. The problem
is that pattern synonym record selectors don't do the same name mangling
as normal datatypes when DuplicateRecordFields is enabled. They could,
but this would require some work to track the field label and selector
name separately.

In particular, we currently represent datatype selectors in the third
component of AvailTC, but pattern synonym selectors are just represented
as Avails (because they don't have a corresponding type constructor).
Moreover, the GlobalRdrElt for a selector currently requires it to have
a parent tycon.

(example due to Adam Gundry)

=== Updating Explicitly Bidirectional Pattern Synonyms ===

Consider the following

```
pattern Silly{a} <- [a] where
  Silly a = [a, a]

f1 = a [5] -- 5

f2 = [5] {a = 6} -- currently [6,6]
```

=== Fixing Polymorphic Updates ===

They were fixed by adding these two lines in `dsExpr`. This might break
record updates but will be easy to fix.

```
+ ; let req_wrap = mkWpTyApps (mkTyVarTys univ_tvs)

- , pat_wrap = idHsWrapper }
+, pat_wrap = req_wrap }
```

=== Mixed selectors error ===

Note [Mixed Record Field Updates]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Consider the following pattern synonym.

    data MyRec = MyRec { foo :: Int, qux :: String }

    pattern HisRec{f1, f2} = MyRec{foo = f1, qux=f2}

This allows updates such as the following

    updater :: MyRec -> MyRec
    updater a = a {f1 = 1 }

It would also make sense to allow the following update (which we
reject).

    updater a = a {f1 = 1, qux = "two" } ==? MyRec 1 "two"

This leads to confusing behaviour when the selectors in fact refer the
same field.

    updater a = a {f1 = 1, foo = 2} ==? ???

For this reason, we reject a mixture of pattern synonym and normal
record selectors in the same update block. Although of course we still
allow the following.

    updater a = (a {f1 = 1}) {foo = 2}

    > updater (MyRec 0 "str")
    MyRec 2 "str"

This patch swaps the order of provided and required constraints in
a pattern signature, so it now goes

      pattern P :: req => prov => t1 -> ... tn -> res_ty

See the long discussion in Trac #10928.

I think I have found all the places, but I could have missed something
particularly in comments.

There is a Haddock changes; so a submodule update.

This patch is driven by Trac #10935, and reinstates the
-fwarn-monomorphism-restriction warning.  It was first lost in 2010:
d2ce0f52 "Super-monster patch implementing the new typechecker -- at
last"

I think the existing documentation is accurate; it is not even
turned on by -Wall.

I added one test.

This patch drops the file level distinction between hs-boot and hsig;
we figure out which one we are compiling based on whether or not there
is a corresponding hs file lying around.

To make the "import A" syntax continue to work for bare hs-boot
files, we also introduce hs-boot merging, which takes an A.hi-boot
and converts it to an A.hi when there is no A.hs file in scope.
This will be generalized in Backpack to merge multiple A.hi files together;
which means we can jettison the "load multiple interface files" functionality.

This works automatically for --make, but for one-shot compilation
we need a new mode: ghc --merge-requirements A will generate an A.hi/A.o
from a local A.hi-boot file; Backpack will extend this mechanism further.

Has Haddock submodule update to deal with change in msHsFilePath behavior.

    - This commit drops support for the hsig extension. Can
      we support it?  It's annoying because the finder code is
      written with the assumption that where there's an hs-boot
      file, there's always an hs file too.  To support hsig, you'd
      have to probe two locations.  Easier to just not support it.

    - #10333 affects us, modifying an hs-boot still doesn't trigger
      recomp.

    - See compiler/main/Finder.hs: this diff is very skeevy, but
      it seems to work.

    - This code cunningly doesn't drop hs-boot files from the
      "drop hs-boot files" module graph, if they don't have a
      corresponding hs file.  I have no idea if this actually is useful.
Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: simonpj, austin, bgamari, spinda

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1098

This patch modifies `error`, `undefined`, and `assertError` to use
implicit call-stacks to provide better error messages to users.

There are a few knock-on effects:

- `GHC.Classes.IP` is now wired-in so it can be used in the wired-in
  types for `error` and `undefined`.

- `TysPrim.tyVarList` has been replaced with a new function
  `TysPrim.mkTemplateTyVars`. `tyVarList` made it easy to introduce
  subtle bugs when you need tyvars of different kinds. The naive

  ```
  tv1 = head $ tyVarList kind1
  tv2 = head $ tyVarList kind2
  ```

  would result in `tv1` and `tv2` sharing a `Unique`, thus substitutions
  would be applied incorrectly, treating `tv1` and `tv2` as the same
  tyvar. `mkTemplateTyVars` avoids this pitfall by taking a list of kinds
  and producing a single tyvar of each kind.

- The types `GHC.SrcLoc.SrcLoc` and `GHC.Stack.CallStack` now live in
  ghc-prim.

- The type `GHC.Exception.ErrorCall` has a new constructor
  `ErrorCallWithLocation` that takes two `String`s instead of one, the
  2nd one being arbitrary metadata about the error (but usually the
  call-stack). A bi-directional pattern synonym `ErrorCall` continues to
  provide the old API.

Updates Cabal, array, and haddock submodules.

Reviewers: nh2, goldfire, simonpj, hvr, rwbarton, austin, bgamari

Reviewed By: simonpj

Subscribers: rwbarton, rodlogic, goldfire, maoe, simonmar, carter,
liyang, bgamari, thomie

Differential Revision: https://phabricator.haskell.org/D861

GHC Trac Issues: #5273

When we are *inferring* the type of a let-bound function,
we might still have a type signature.  And we must be sure
to quantify over its type variables, else you get the crash
in Trac #10615.

See Note [Which type variables to quantify] in TcSimplify

When examining #10615, I found the wildcard handling hard
to understand.  This patch refactors quite a bit, but with
no real change in behaviour.

 * Split out TcIdSigInfo from TcSigInfo, as a separate type,
   like TcPatSynInfo.

 * Make TcIdSigInfo express more invariants by pushing the
   wildard info into TcIdSigBndr

 * Remove all special treatment of unification variables that arise
   from wildcards; so the TauTv of TcType.MetaInfo loses its Bool
   argument.

A ton of konck on changes.  The result is significantly simpler, I think.

The provoking cause for this patch is Trac #5001, comment:23.  There
was an INLINE pragma in an instance decl, that shouldn't be there.
But there was no complaint, just a  mysterious WARN later.

I ended up having to do some real refactoring but the result is,
I think, simpler and more robust.

This fixes Trac #10083.

The key change is in TcBinds.tcValBinds, where we construct
the prag_fn.  With this patch we add a NOINLINE pragma for
any functions that were exported by the hs-boot file for this
module.

See Note [Inlining and hs-boot files], and #10083, for details.

The commit touches several other files becuase I also changed the
representation of the "pragma function" from a function TcPragFun
to an environment, TcPragEnv. This makes it easer to extend
during construction.

Make tuple constraints be handled by a perfectly ordinary
type class, with the component constraints being the
superclasses:
    class (c1, c2) => (c2, c2)

This change was provoked by

  #10359  inability to re-use a given tuple
          constraint as a whole

  #9858   confusion between term tuples
          and constraint tuples

but it's generally a very nice simplification. We get rid of
 -  In Type, the TuplePred constructor of PredTree,
    and all the code that dealt with TuplePreds
 -  In TcEvidence, the constructors EvTupleMk, EvTupleSel

See Note [How tuples work] in TysWiredIn.

Of course, nothing is ever entirely simple. This one
proved quite fiddly.

- I did quite a bit of renaming, which makes this patch
  touch a lot of modules. In partiuclar tupleCon -> tupleDataCon.

- I made constraint tuples known-key rather than wired-in.
  This is different to boxed/unboxed tuples, but it proved
  awkward to have all the superclass selectors wired-in.
  Easier just to use the standard mechanims.

- While I was fiddling with known-key names, I split the TH Name
  definitions out of DsMeta into a new module THNames.  That meant
  that the known-key names can all be gathered in PrelInfo, without
  causing module loops.

- I found that the parser was parsing an import item like
      T( .. )
  as a *data constructor* T, and then using setRdrNameSpace to
  fix it.  Stupid!  So I changed the parser to parse a *type
  constructor* T, which means less use of setRdrNameSpace.

  I also improved setRdrNameSpace to behave better on Exact Names.
  Largely on priciple; I don't think it matters a lot.

- When compiling a data type declaration for a wired-in thing like
  tuples (,), or lists, we don't really need to look at the
  declaration.  We have the wired-in thing!  And not doing so avoids
  having to line up the uniques for data constructor workers etc.
  See Note [Declarations for wired-in things]

- I found that FunDeps.oclose wasn't taking superclasses into
  account; easily fixed.

- Some error message refactoring for invalid constraints in TcValidity

- Haddock needs to absorb the change too; so there is a submodule update

This reverts commit fb54b2c1.

As Alan pointed out, this will make cherry picking a lot harder until
7.10.2, so lets back it out until after the release.

At the moment ghc-exactprint, which uses the GHC API Annotations to
provide a framework for roundtripping Haskell source code with optional
AST edits, has to implement a horrible workaround to manage the points
where layout needs to be captured.

These are

    MatchGroup
    HsDo
    HsCmdDo
    HsLet
    LetStmt
    HsCmdLet
    GRHSs

To provide a more natural representation, the contents subject to layout
rules need to be wrapped in a SrcSpan.

This commit does this.

Trac ticket #10250

Reviewed By: austin

Differential Revision: https://phabricator.haskell.org/D815

GHC Trac Issues: #10250

Previously (Trac #10351) we could get

    Non type-variable argument in the constraint: C [t]
    (Use FlexibleContexts to permit this)
    When checking that `f' has the inferred type
      f :: forall t. C [t] => t -> ()

which is a bit stupid: we have *inferred* a type that we
immediately *reject*.  This patch arranges that that the
generalisation mechanism (TcSimplify.decideQuantification)
doesn't pick a predicate that will be rejected by the
subsequent validity check.

This forced some minor refactoring, as usual.

This is a minor refactoring, but it simplifies the code quite a bit

* Decrease the number of variants of tcExtend in TcEnv
* Remove "not_actually_free" from TcEnv.tc_extend_local_env2
* Simplify plumbingof the "closed" flag
* Remove redundant scoping of wild-card variables

Summary:
SPJ's solution is to only bring the `TcId` (which includes the type) of a
binder into scope when it had a non-partial type signature.

Take care of this by only storing the `TcId` in `TcSigInfo` of non-partial
type signatures, hence the change to `sig_poly_id :: Maybe TcId`. Only in case
of a `Just` will we bring the `TcId` in scope. We still need to know the name
of the binder, even when it has a partial type signature, so add a `sig_name
:: Name` field. The field `sig_partial :: Bool` is no longer necessary, so
reimplement `isPartialSig` in terms of `sig_poly_id`.

Note that the new test case fails, but not because of a panic, but because the
`Num a` constraint is missing. Adding an extra-constraints wildcard to
`copy`'s signature would fix it.

Test Plan: validate

Reviewers: simonpj, austin

Reviewed By: simonpj

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D646

GHC Trac Issues: #10045

Richard was interrogating me about decideQuantification yesterday.
I got a bit stuck on the promote_tvs part. This refactoring

 * simplifes the API of decideQuantification

 * move mkMinimalBySCs into decideQuantification (a better place for it)

 * moves promotion out of decideQuantification (where it didn't really
   fit), and comments much more fully what is going on with the promtion stuff

 * comments decideQuantification more fully

 * coments the EqPred case of quantifyPred more fully

It turned out that the theta returned by decideQuantification,
and hence by simplifyInfer, is now fully zonked, so I could remove
a zonking in TcBinds.

Summary:
IPs with this type will always be solved for the current source
location. If another IP of the same type is in scope, the two locations will be
appended, creating a call-stack. The Location type is kept abstract so users
cannot create them, but a Location can be turned into a list of SrcLocs, which
correspond to individual locations in a program. Each SrcLoc contains a
package/module/file name and start/end lines and columns.

The only thing missing from the SrcLoc in my opinion is the name of the
top-level definition it inhabits. I suspect that would also be useful, but it's
not clear to me how to extract the current top-level binder from within the
constraint solver. (Surely I'm just missing something here?)

I made the (perhaps controversial) decision to have GHC completely ignore
the names of Location IPs, meaning that in the following code:

    bar :: (?myloc :: Location) => String
    bar = foo

    foo :: (?loc :: Location) => String
    foo = show ?loc

if I call `bar`, the resulting call-stack will include locations for

1. the use of `?loc` inside `foo`,
2. `foo`s call-site inside `bar`, and
3. `bar`s call-site, wherever that may be.

This makes Location IPs very special indeed, and I'm happy to change it if the
dissonance is too great.

I've also left out any changes to base to make use of Location IPs, since there
were some concerns about a snowball effect. I think it would be reasonable to
mark this as an experimental feature for now (it is!), and defer using it in
base until we have more experience with it. It is, after all, quite easy to
define your own version of `error`, `undefined`, etc. that use Location IPs.

Test Plan: validate, new test-case is testsuite/tests/typecheck/should_run/IPLocation.hs

Reviewers: austin, hvr, simonpj

Reviewed By: simonpj

Subscribers: simonmar, rodlogic, carter, thomie

Differential Revision: https://phabricator.haskell.org/D578

GHC Trac Issues: #9049

Summary:
HsTyLit now has SourceText

Update documentation of HsSyn to reflect which annotations are attached to which element.

Ensure that the parser always keeps HsSCC and HsTickPragma values, to
be ignored in the desugar phase if not needed

Bringing in SourceText for pragmas

Add Location in NPlusKPat

Add Location in FunDep

Make RecCon payload Located

Explicitly add AnnVal to RdrName where it is compound

Add Location in IPBind

Add Location to name in IEThingAbs

Add Maybe (Located id,Bool) to Match to track fun_id,infix
  This includes converting Match into a record and adding a note about why
  the fun_id needs to be replicated in the Match.

Add Location in KindedTyVar

Sort out semi-colons for parsing

  - import statements
  - stmts
  - decls
  - decls_cls
  - decls_inst

This updates the haddock submodule.

Test Plan: ./validate

Reviewers: hvr, austin, goldfire, simonpj

Reviewed By: simonpj

Subscribers: thomie, carter

Differential Revision: https://phabricator.haskell.org/D538

The provoking cause was Trac #5821, which concerned
type families, but in fixing it I did the usual round
of tidying up and docmenting.

The main comment is now
    Note [Handling SPECIALISE pragmas]
in TcBinds.

It is "wrinkle 2" that fixes #5821.