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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 fixes Trac #11351.   The implementation is pretty
simple, happily.

I took the opportunity to re-order the prov/req context
in builder-ids, which was confusingly backwards.

Some modest refactoring, triggered in part by Trac #11051

* Kill off PatSynId, ReflectionId in IdDetails
  They were barely used, and only for pretty-printing

* Add helper function Id.mkExportedVanillaId, and use it

* Polish up OccName.isDerivedOccName, as a predicate for
  definitions generated internally by GHC, which we
  might not want to show to the user.

* Kill off unused OccName.mkDerivedTyConOcc

* Shorten the derived OccNames for newtype and data
  instance axioms

* A bit of related refactoring around newFamInstAxiomName

This bug was thrown up by Trac #11361, but I found that the
problem was deeper: GHC was allowing

  class C a where
    type F (a :: k) :: *
    type F (x :: *) = x    -- Not right!

(Which is now indexed-types/should_compile/T11361a.)

Anyway the fix is relatively simple; use tcMatchTys in
tcDefaultAssocDecl.

Merge to 8.0 branch.

Previously tcMatchTys took a set of "template type variables" to
bind.  But all the calls are top-level, and we always want to
bind all variables in the template.  So I simplified the API
by omitting that argument.

There should be no change in behaviour.

Feel free to merge to 8.0 if it helps in merging other patches

I missed a crucial step in the wiring-in process of `CallStack` in D861,
the bit where you actually wire-in the Name... This led to a nasty bug
where GHC thought `CallStack` was not wired-in and tried to fingerprint
it, which failed because the defining module was not loaded.

But we don't need `CallStack` to be wired-in anymore since `error` and
`undefined` no longer need to be wired-in. So we just remove them all.

Updates haddock submodule.

Test Plan: `./validate` and `make slowtest TEST=tc198`

Reviewers: simonpj, goldfire, austin, hvr, bgamari

Reviewed By: simonpj, bgamari

Subscribers: goldfire, thomie

Projects: #ghc

Differential Revision: https://phabricator.haskell.org/D1739

GHC Trac Issues: #11331

Test Plan: validate, check that gz is used

Reviewers: hvr, austin, thomie

Reviewed By: thomie

Differential Revision: https://phabricator.haskell.org/D1788

GHC Trac Issues: #11434

Reviewers: austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1790

GHC Trac Issues: #11414

Kind equalities changed how `*`/`#` are represented internally, which
means that showing a `TypeRep` that contains either of those kinds
produces a rather gross-looking result, e.g.,

```
> typeOf (Proxy :: Proxy 'Just)
Proxy (TYPE 'Lifted -> Maybe (TYPE 'Lifted)) 'Just
```

We can at least special-case the `Show` instance for `TypeRep` so that
it prints `*` to represent `TYPE 'Lifted` and `#` to represent `TYPE
'Unlifted`.

Addresses one of the issues uncovered in #11334.

Test Plan: ./validate

Reviewers: simonpj, hvr, austin, goldfire, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1757

GHC Trac Issues: #11334

Fix operator completions: list of suitable completions only rather than
everything from imported modules.
Signed-off-by: Arthur Fayzrakhmanov (Артур Файзрахманов) <heraldhoi@gmail.com>

ghc: fix operator completions

Reviewers: austin, hvr, thomie, bgamari

Reviewed By: thomie, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1058

GHC Trac Issues: #10576

Test Plan: Build then clean

Reviewers: austin, thomie

Reviewed By: thomie

Differential Revision: https://phabricator.haskell.org/D1786

GHC Trac Issues: #11433

Test Plan: Validate

Reviewers: simonmar, austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1787

GHC Trac Issues: #11300

As a result of some other unrelated changes I found that
IndTypesPerf was failing, and opened Trac #11408.  There's
a test in indexed-types/should-compile/T11408.

The bug was that a type like
 forall t. (MT (UL t) (UR t) ~ t) => UL t -> UR t -> Int
is in fact unambiguous, but it's a bit subtle to prove
that it is unambiguous.

In investigating, Dimitrios and I found several subtle
bugs in the constraint solver, fixed by this patch

* canRewrite was missing a Derived/Derived case.  This was
  lost by accident in Richard's big kind-equality patch.

* Interact.interactTyVarEq would discard [D] a ~ ty if there
  was a [W] a ~ ty in the inert set.  But that is wrong because
  the former can rewrite things that the latter cannot.
  Fix: a new function eqCanDischarge

* In TcSMonad.addInertEq, the process was outright wrong for
  a Given/Wanted in the (GWModel) case.  We were adding a new
  Derived without kicking out things that it could rewrite.
  Now the code is simpler (no special GWModel case), and works
  correctly.

* The special case in kickOutRewritable for [W] fsk ~ ty,
  turns out not to be needed.  (We emit a [D] fsk ~ ty which
  will do the job.

I improved comments and documentation, esp in TcSMonad.

Summary:
Certain syntactic elements have integers in them, such as fixity
specifications, SPECIALISE pragmas and so on.

The lexer will accept mult-radix literals, with arbitrary leading zeros
in these.

Bring in a SourceText field to each affected AST element to capture the
original literal text for use with API Annotations.

Affected hsSyn elements are

```
     -- See note [Pragma source text]
     data Activation = NeverActive
                     | AlwaysActive
                     | ActiveBefore SourceText PhaseNum
                          -- Active only *strictly before* this phase
                     | ActiveAfter SourceText PhaseNum
                           -- Active in this phase and later
                     deriving( Eq, Data, Typeable )
                               -- Eq used in comparing rules in HsDecls

     data Fixity = Fixity SourceText Int FixityDirection
       -- Note [Pragma source text]
       deriving (Data, Typeable)
 ```

and

```
      | HsTickPragma         -- A pragma introduced tick
         SourceText           -- Note [Pragma source text] in BasicTypes
         (StringLiteral,(Int,Int),(Int,Int))
                                          -- external span for this tick
         ((SourceText,SourceText),(SourceText,SourceText))
            -- Source text for the four integers used in the span.
            -- See note [Pragma source text] in BasicTypes
         (LHsExpr id)
```

Updates haddock submodule

Test Plan: ./validate

Reviewers: goldfire, bgamari, austin

Reviewed By: bgamari

Subscribers: thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D1781

GHC Trac Issues: #11430

Differential Revision: https://phabricator.haskell.org/D1785

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.

We now check for unused variables one at a time, instead of
all at the top.

Test: dependent/should_compile/T11405

This addresses #11405, but a deeper problem lurks.
Try test dependent/should_compile/T11405 and see comment:3
on the ticket.

This moves the call to tcSubType into the context of the
checkInstConstraints call, allowing the deferred type error
somewhere to hang its hat.

This is mentioned in #11376.

All things of kind *, including * itself, need to have a PtrRep.

Test: dependent/should_compile/T11311

This moves the duplicate-unique check from knownKeyNames (which omits
TH) to allKnownKeyNames (which includes TH).

This one worked for me out of the box.

Previously, the check for impredicative type applications was
in the wrong spot.

Test case: typecheck/should_fail/T11355

Before, it was possible to have a datatypes such as

```
type ConstantT a b = a
newtype T (f :: * -> *) (a :: ConstantT * f) = T (f a) deriving Functor

data family TFam (f :: * -> *) (a :: *)
newtype instance TFam f (ConstantT a f) = TFam (f a) deriving Functor
```

fail to eta-reduce because either (1) a TyVar had a kind synonym that
mentioned another TyVar, or (2) an instantiated type was itself a type
synonym that mentioned another TyVar. A little bit of tweaking to
`expandTypeSynonyms` and applying it before the eta-reduction check in
the `deriving` machinery is sufficient to fix this.

Fixes #11416.

Test Plan: ./validate

Reviewers: goldfire, simonpj, austin, bgamari

Reviewed By: simonpj

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1772

GHC Trac Issues: #11416

But still disallow empty pattern synonym builder declarations. Handling
this incorrectly was the cause of #11367.

Test Plan: ./validate

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1779

GHC Trac Issues: #11367

Reviewers: austin, bgamari, thomie

Reviewed By: thomie

Subscribers: angerman, thomie, erikd

Differential Revision: https://phabricator.haskell.org/D1775

Test Plan: ./validate

Reviewers: goldfire, austin, bgamari, simonpj

Subscribers: simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D1766

GHC Trac Issues: #11345

Test Plan: Validate

Reviewers: austin, thomie, nomeata

Differential Revision: https://phabricator.haskell.org/D1782

GHC Trac Issues: #11433

Resolves #11434.