GitLab

This patch was triggered by Trac #11601, where I discovered that
-XStrict was really not doing the right thing. In particular,

  f y = let !(Just x) = blah[y] in body[y,x]

This was evaluating 'blah' but not pattern matching it
against Just until x was demanded.  This is wrong.

The patch implements a new semantics which ensures that strict
patterns (i.e. ones with an explicit bang, or with -XStrict)
are evaluated fully when bound.

* There are extensive notes in DsUtils:
  Note [mkSelectorBinds]

* To do this I found I need one-tuples;
  see Note [One-tuples] in TysWiredIn

I updated the user manual to give the new semantics

See Note [TYPE] in TysPrim. There are still some outstanding
pieces in #11471 though, so this doesn't actually nail the bug.

This commit also contains a few performance improvements:

* Short-cut equality checking of nullary type syns

* Compare types before kinds in eqType

* INLINE coreViewOneStarKind

* Store tycon binders separately from kinds.

This resulted in a ~10% performance improvement in compiling
the Cabal package. No change in functionality other than
performance. (This affects the interface file format, though.)

This commit updates the haddock submodule.

In poking Trac #11414 I found myself sinking into the abe_inst_wrap
swamp.  What is this strange thing?  (It turned out that #11414 was
breaking because of it.)

Thrillingly, I found a way to sweep it away again, putting the deep
instantation into tcMonoBinds instead of mkExport; and it turned out
that the fun_co_fn field of FunBind was already there ready to receive
exactly this wrapper. Hooray.  Result

* Death to abe_inst_wrap
* Death to mbi_orig
* Death to the plumbing in tcPolyInfer that did the
  deep instantiation

I did find that I had to re-engineer the treatment of instance type
signatures (again), but the result looks more modular and robust to
me.

And #11414 is fixed.

Summary:
In the past the canonical way for constructing an SDoc string literal was the
composition `ptext . sLit`.  But for some time now we have function `text` that
does the same.  Plus it has some rules that optimize its runtime behaviour.
This patch takes all uses of `ptext . sLit` in the compiler and replaces them
with calls to `text`.  The main benefits of this patch are clener (shorter) code
and less dependencies between module, because many modules now do not need to
import `FastString`.  I don't expect any performance benefits - we mostly use
SDocs to report errors and it seems there is little to be gained here.

Test Plan: ./validate

Reviewers: bgamari, austin, goldfire, hvr, alanz

Subscribers: goldfire, thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D1784

This adds a new variant of AbsBinds that is used solely for bindings
with a type signature. This allows for a simpler desugaring that
does not produce the bogus output that tripped up Core Lint in
ticket #11405. Should make other desugarings simpler, too.

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.

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

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

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

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.

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.

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.

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

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

Comes with Haddock submodule update.
Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Summary:
Instead of doing these warnings at MkIface time, we do them
when we create the instances/rules in the typechecker/desugarer.

Emitting warnings for auto-generated instances was a pain
(since the specialization monad doesn't have the capacity
to emit warnings) so instead I just deprecated -fwarn-auto-orphans.
Auto rule orphans are pretty harmless anyway: they don't cause
interface files to be eagerly loaded in.
Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: simonpj, austin, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1297

Previously CallStacks would be built using String, which would pull in
GHC.Base while compiling GHC.Err. Use [Char] instead.

The default top-level exception handler now uses the `Show` instance for
`ErrorCall` when printing exceptions, so it will actually print the out-of-band
data (e.g. `CallStack`s) in compiled binaries, instead of just printing the
error message.

This also updates the hpc submodule to fix the test output.

Reviewed By: austin, thomie

Differential Revision: https://phabricator.haskell.org/D1217

Fixes Trac #10721.
See Note [SPECIALISE on INLINE functions]

This change avoids a spurious WARNing from mkCast.  In the output of
the desugarer (only, I think) we can have a cast where the type of the
expression and cast don't syntactically match, because of an enclosing
type-let binding.

Depends on D864.

Previous behaviour was ErrorCall, which might mask issues in tests 
using -fdefer-type-errors
Signed-off-by: David Kraeutmann <kane@kane.cx>

Test Plan: Test whether the error thrown is indeed TypeError and not 
ErrorCall.

Reviewers: hvr, nomeata, austin

Reviewed By: nomeata, austin

Subscribers: nomeata, simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D866

GHC Trac Issues: #10284

This should fix T10348

Summary:
If we have an orphan rule in our database, don't apply it
unless the defining module is transitively imported by the
module we are processing.  We do this by defining a new RuleEnv
data type which includes both the RuleBase as well as the set
of visible orphan modules, and threading this through the
relevant environments (CoreReader, RuleCheckEnv and ScEnv).

This is analogous to the instances fix we applied in #2182
4c834fdd, but done for RULES.
An important knock-on effect is that we can remove some buggy
code in LoadInterface which tried to avoid loading interfaces
that were loaded by plugins (which sometimes caused instances
and rules to NEVER become visible).

One note about tests: I renamed the old plugins07 test to T10420
and replaced plugins07 with a test to ensure that a plugin
import did not cause new rules to be loaded in.
Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: simonpj, austin, goldfire

Subscribers: bgamari, thomie

Differential Revision: https://phabricator.haskell.org/D950

GHC Trac Issues: #10420

An upcoming commit means that the RULES for 'seq' get only
one value arg, not two.  This patch prepares for that by

- reducing the arity of seq's built-in rule, to take one value arg
- making 'seq' not inline on the LHS of RULES
- and removing the horrid un-inlining in DsBinds.decomposeRuleLhs

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 multiple commits from Simon:

  - 04a484ea Test Trac #10359
  - a9ccd37a Test Trac #10403
  - c0aae6f6 Test Trac #10248
  - eb6ca851 Make the "matchable-given" check happen first
  - ca173aa3 Add a case to checkValidTyCon
  - 51cbad15 Update haddock submodule
  - 6e1174da Separate transCloVarSet from fixVarSet
  - a8493e03 Fix imports in HscMain (stage2)
  - a154944b Two wibbles to fix the build
  - 5910a1bc Change in capitalisation of error msg
  - 130e93aa Refactor tuple constraints
  - 8da785d5 Delete commented-out line

These break the build by causing Haddock to fail mysteriously when
trying to examine GHC.Prim it seems.

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

More fallout from the silent-superclass refactoring; nothing drastic.
Fixes Trac #10335.

The changes are:
  1. No impredicative types in `Typeable`
  2. Distinguish normal tuples, from tuples of constraints.

Note [Bind new Givens immediately] in TcRnTypes

We were never using the generality.  Result: less code, more efficient.
Cake for everyone.

We were erroneously quantifying over the function when it
had a dictionary type. A bit pathological, but possible.

This fixes Trac #10251

Summary:
This implements the new `Typeable` solver: when GHC sees `Typeable` constraints
it solves them on the spot.

The current implementation creates `TyCon` representations on the spot.

Pro: No overhead at all in code that does not use `Typeable`
Cons: Code that uses `Typeable` may create multipe `TyCon` represntations.

We have discussed an implementation where representations of `TyCons` are
computed once, in the module, where a datatype is declared.  This would
lead to more code being generated:  for a promotable datatype we need to
generate `2 + number_of_data_cons` type-constructro representations,
and we have to do that for all programs, even ones that do not intend to
use typeable.

I added code to emit warning whenevar `deriving Typeable` is encountered---
the idea being that this is not needed anymore, and shold be fixed.

Also, we allow `instance Typeable T` in .hs-boot files, but they result
in a warning, and are ignored.  This last one was to avoid breaking exisitng
code, and should become an error, eventually.

Test Plan:
1. GHC can compile itself.
2. I compiled a number of large libraries, including `lens`.
    - I had to make some small changes:
      `unordered-containers` uses internals of `TypeReps`, so I had to do a 1 line fix
    - `lens` needed one instance changed, due to a poly-kinded `Typeble` instance

3. I also run some code that uses `syb` to traverse a largish datastrucutre.
I didn't notice any signifiant performance difference between the 7.8.3 version,
and this implementation.

Reviewers: simonpj, simonmar, austin, hvr

Reviewed By: austin, hvr

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D652

GHC Trac Issues: #9858

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

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.

The idea was promted by Trac #9939, but it was Christmas, so I did
some recreational programming that went much further.

The idea is to warn when a constraint in a user-supplied context is
redundant.  Everything is described in detail in
  Note [Tracking redundant constraints]
in TcSimplify.

Main changes:

 * The new ic_status field in an implication, of type ImplicStatus.
   It replaces ic_insol, and includes information about redundant
   constraints.

 * New function TcSimplify.setImplicationStatus sets the ic_status.

 * TcSigInfo has sig_report_redundant field to say whenther a
   redundant constraint should be reported; and similarly
   the FunSigCtxt constructor of UserTypeCtxt

 * EvBinds has a field eb_is_given, to record whether it is a given
   or wanted binding. Some consequential chagnes to creating an evidence
   binding (so that we record whether it is given or wanted).

 * AbsBinds field abs_ev_binds is now a *list* of TcEvBiinds;
   see Note [Typechecking plan for instance declarations] in
   TcInstDcls

 * Some significant changes to the type checking of instance
   declarations; Note [Typechecking plan for instance declarations]
   in TcInstDcls.

 * I found that TcErrors.relevantBindings was failing to zonk the
   origin of the constraint it was looking at, and hence failing to
   find some relevant bindings.  Easy to fix, and orthogonal to
   everything else, but hard to disentangle.

Some minor refactorig:

 * TcMType.newSimpleWanteds moves to Inst, renamed as newWanteds

 * TcClassDcl and TcInstDcls now have their own code for typechecking
   a method body, rather than sharing a single function. The shared
   function (ws TcClassDcl.tcInstanceMethodBody) didn't have much code
   and the differences were growing confusing.

 * Add new function TcRnMonad.pushLevelAndCaptureConstraints, and
   use it

 * Add new function Bag.catBagMaybes, and use it in TcSimplify