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Because garbage collector calls `retainerProfile()` and `heapCensus()`,
GC times normally include some of PROF times too. To fix this we have
these lines:

    // heapCensus() is called by the GC, so RP and HC time are
    // included in the GC stats.  We therefore subtract them to
    // obtain the actual GC cpu time.
    stats.gc_cpu_ns      -=  prof_cpu;
    stats.gc_elapsed_ns  -=  prof_elapsed;

These variables are later used for calculating GC time excluding the
final GC (which should be attributed to EXIT).

    exit_gc_elapsed      = stats.gc_elapsed_ns - start_exit_gc_elapsed;

The problem is if we subtract PROF times from `gc_elapsed_ns` and then
subtract `start_exit_gc_elapsed` from the result, we end up subtracting
PROF times twice, because `start_exit_gc_elapsed` also includes PROF
times.

We now subtract PROF times from GC after the calculations for EXIT and
MUT times. The existing assertion that checks

    INIT + MUT + GC + EXIT = TOTAL

now holds. When we subtract PROF numbers from GC, and a new assertion

    INIT + MUT + GC + PROF + EXIT = TOTAL

also holds.

Fixes #15897. New assertions added in this commit also revealed #16102,
which is also fixed by this commit.

UNDERFLOW_FRAMEs don't have profiling headers so we have to use the
AP_STACK's function's CCS as the new frame's CCS.

Fixes one of the many bugs caught by concprog001 (#15508).

Summary:
This fixes #15471

In the typechecker we check that the splice has the right type but we
crucially don't zonk the generated expression. This is because we might
end up unifying type variables from outer scopes later on.

Reviewers: simonpj, goldfire, bgamari

Subscribers: rwbarton, carter

GHC Trac Issues: #15471

Differential Revision: https://phabricator.haskell.org/D5286

Summary:
We currently permit any and all uses of unsaturated type
synonyms and type families in GHCi's `:kind` command, which allows
strange interactions like this one:

```
> :set -XTypeFamilies -XPolyKinds
> type family Id (a :: k)
> type instance Id a = a
> type Foo x = Maybe
> :kind! Id Foo
```

This is probably a stretch too far, so this patch moves to disallow
unsaturated synonyms that aren't at the top level (we still want to
allow `:kind Id`, for instance). We do this by augmenting `GhciCtxt`
with an additional `Bool` field to indicate if we are at the
outermost level of the type being passed to `:kind` or not. See
`Note [Unsaturated type synonyms in GHCi]` in `TcValidity` for the
full story.

Test Plan: make test TEST=T16013

Reviewers: goldfire, bgamari

Reviewed By: goldfire

Subscribers: simonpj, goldfire, rwbarton, carter

GHC Trac Issues: #16013

Differential Revision: https://phabricator.haskell.org/D5471

Warn users when -XDerivingStrategies is enabled but not used, at each
potential use site.

add -Wmissing-deriving-strategies

Reviewers: bgamari, RyanGlScott

Subscribers: andrewthad, rwbarton, carter

GHC Trac Issues: #15798

Differential Revision: https://phabricator.haskell.org/D5451

Summary:
This patch implements visible kind application (GHC Proposal 15/#12045), as well as #15360 and #15362.
It also refactors unnamed wildcard handling, and requires that type equations in type families in Template Haskell be
written with full type on lhs. PartialTypeSignatures are on and warnings are off automatically with visible kind
application, just like in term-level.

There are a few remaining issues with this patch, as documented in
ticket #16082.

Includes a submodule update for Haddock.

Test Plan: Tests T12045a/b/c/TH1/TH2, T15362, T15592a

Reviewers: simonpj, goldfire, bgamari, alanz, RyanGlScott, Iceland_jack

Subscribers: ningning, Iceland_jack, RyanGlScott, int-index, rwbarton, mpickering, carter

GHC Trac Issues: `#12045`, `#15362`, `#15592`, `#15788`, `#15793`, `#15795`, `#15797`, `#15799`, `#15801`, `#15807`, `#15816`

Differential Revision: https://phabricator.haskell.org/D5229

Support for Mac OS X on PowerPC has been dropped by Apple years ago. We
follow suit and remove PowerPC support for Darwin.

Fixes #16106.

This disables `ghcilink005`, `foreignInterruptable`, and `T7040_ghci` in
the unregisterised build as they tend to fail non-deterministically. See
ticket #16085.

As noted in #16085 this test is fragile in unregisterised compilers.

 * Mark arith011 as broken with integer-simple

   As noted in #16091, arith011 fails when run against integer-simple with a
   "divide by zero" exception. This suggests that integer-gmp and integer-simple
   are handling division by zero differently.

 * This also fixes broken_without_gmp; the lack of types made the previous
   failure silent, sadly. Improves situation of #16043.

 * Mark several tests implicitly depending upon integer-gmp as broken
   with integer-simple. These expect to see Core coming from integer-gmp,
   which breaks with integer-simple.

 * Increase runtime timeout multiplier of T11627a with integer-simple

   I previously saw that T11627a timed out in all profiling ways when run against
   integer-simple. I suspect this is due to integer-simple's rather verbose heap
   representation. Let's see whether increasing the runtime timeout helps.

   Fixes test for #11627.

This is all in service of fixing #16043.

The retainer profiler no longer uses the C stack for its mark stack (#14758).
Consequently even the small C stack provided on Darwin should be sufficient to
run this test. See #11627

Currently we duplicate top-level binder ids for no reason:

    $fEqHsExpr_$c/=
    $fEqHsExpr_$c/=
      = \ @ id_a27U $dEq_a27V eta_B2 eta1_B1 ->
          case $fEqHsExpr_$c== $dEq_a27V eta_B2 eta1_B1 of {
            False -> True;
            True -> False
          }

with this patch we drop the first line when type signatures are not
printed (-dsuppress-type-signatures, which is implied by -dsuppress-all)

Reviewers: simonpj, bgamari

Reviewed By: simonpj

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5472

This is due to the failures documented in #16087. The condition here could be
improved as it matches on `BUILD_FLAVOUR` instead of looking at the compiler
flags. However, it's better than nothing and I hope we will be able to fix these
issues before long.

As documented in #15382, this is known to fail in prof_hc_hb on i386.
Concerningly, I have also seen this test non-deterministically fail in
prof_hc_hb on amd64. We should really investigate this.

As noted in #15662, these used to be broken on Darwin due to a Clang toolchain
bug. However, this bug appears to be fixed in the Clang shipped with macOS
Mojave. Unfortunately, we don't really have any way to only mark it as broken on
certain operation system releases so I am just removing the expect_broken
entirely.

Trac #16038 exposed the fact that TcRnDriver.checkHiBootIface
was creating a binding, in the module being compiled, for
   $fxBlah = $fBlah

 but $fxBlah was a /GlobalId/. But all bindings should be for
 /LocalIds/ else dependency analysis goes down the tubes.

* I added a CoreLint check that an occurrence of a GlobalId
  is not bound by an binding of a LocalId.  (There is already
  a binding-site check that no binding binds a GlobalId.)

* I refactored (and actually signficantly simplified) the
  tricky code for dfuns in checkHiBootIface to ensure that
  we get LocalIds for those boot-dfuns.

Alas, I then got "duplicate instance" messages when compiling
HsExpr. It turns out that this is a long-standing, but extremely
delicate, bug: even before this patch, if you compile HsExpr
with -ddump-tc-trace, you get "duplicate instance". Without
-ddump-tc-trace, it's OK.  What a mess!

The reason for the duplicate-instance is now explained in
Note [Loading your own hi-boot file] in LoadIface.  I fixed
it by a Gross Hack in LoadIface.loadInterface. This is at
least no worse than before.

But there should be a better way. I have opened #16081 for this.

candidateQTyVars was failing to return fully-zonked
tyvars, and that made things fall over chaotically
when we try to sort them into a well-scoped telescope.
Result: Trac #15795

So I made candidateQTvs guarantee to have fully-zonked
tyvars (i.e. with zonked kinds).  That's a bit annoying
but not really difficult.

Summary:
The validity check which rejected things like:

```lang=haskell
type family B x where
  A x = x
```

Used to live in the typechecker. But it turns out that this validity
check was //only// being run on closed type families without CUSKs!
This meant that GHC would silently accept something like this:

```lang=haskell
type family B (x :: *) :: * where
  A x = x
```

This patch fixes the issue by moving this validity check to the
renamer, where we can be sure that the check will //always// be run.

Test Plan: make test TEST=T16002

Reviewers: simonpj, bgamari

Reviewed By: simonpj

Subscribers: goldfire, rwbarton, carter

GHC Trac Issues: #16002

Differential Revision: https://phabricator.haskell.org/D5420

When we pretty-print types, we suppress RuntimeRep variables, but
we were being too aggressive in doing so, resulting in Trac #16074.

This patch makes the suppression a bit less aggressive.
See Note [Defaulting RuntimeRep variables]

This call plain missing, and as a result the casts
messed up deep-skolemisation in tcSubType

Fixes Trac #16033

Summary:
GHCi's `:info` command was pretty-printined GADT
constructors suboptimally in the following ways:

1. Sometimes, fields were parenthesized when they did not need it,
   e.g.,

```lang=haskell
data Foo a where
  MkFoo :: (Maybe a) -> Foo a
```

   I fixed this by refactoring some code in `pprIfaceConDecl` to be a
   little smarter with respect to GADT syntax. See `pprFieldArgTy`
   and `pprArgTy`.
2. With `-fprint-explicit-kinds` enabled, there would be times when
   specified arguments would be printed without a leading `@` in GADT
   return types, e.g.,

```lang=haskell
data Bar @k (a :: k) where
  MkBar :: Bar k a
```

   It turns out that `ppr_tc_app`, the function which pretty-prints
   these return types, was not using the proper machinery to print
   out the arguments, which caused the visibilities to be forgotten
   entirely. I refactored `ppr_tc_app` to do this correctly.

Test Plan: make test TEST=T16030

Reviewers: goldfire, bgamari, simonpj

Reviewed By: simonpj

Subscribers: simonpj, rwbarton, carter

GHC Trac Issues: #16030

Differential Revision: https://phabricator.haskell.org/D5440

Summary:
See #8959, this is one more place where we
can pretty-print Unicode syntax.

Test Plan: validate

Reviewers: nomeata, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, carter

GHC Trac Issues: #8959

Differential Revision: https://phabricator.haskell.org/D5439

Summary: Rank2Types is deprecated. Don't suggest to users to use it.

Reviewers: bgamari, RyanGlScott, simonpj

Reviewed By: RyanGlScott, simonpj

Subscribers: RyanGlScott, rwbarton, carter

GHC Trac Issues: #16000

Differential Revision: https://phabricator.haskell.org/D5447

`ghci -fno-implicit-import-qualified` didn't start with error message:

```
GHCi, version 8.6.2: http://www.haskell.org/ghc/  :? for help

<interactive>:1:6: error:
    Not in scope: ‘System.IO.hSetBuffering’
        No module named ‘System.IO’ is imported.

...
```

This change fixes it and update test T2452 to cover this.

Test Plan:
  TEST=T2452 make accept

harbormaster build runs

Reviewers: simonmar, bgamari, RyanGlScott

Reviewed By: simonmar

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5452

Also use 'id'

Spurious changes observed in a integer-simple build. In service of #16043.

This fixes a variety of testsuite failures with integer-simple of the form

```
--- typecheck/should_fail/tcfail072.run/tcfail072.stderr.normalised
+++ typecheck/should_fail/tcfail072.run/tcfail072.comp.stderr.normalised
@@ -12,7 +12,7 @@
           -- Defined in ‘integer-<IMPL>-<VERSION>:GHC.Integer.Type’
         instance Ord () -- Defined in ‘GHC.Classes’
         ...plus 21 others
-        ...plus three instances involving out-of-scope types
+        ...plus two instances involving out-of-scope types
         (use -fprint-potential-instances to see them all)
      In the expression: g A
       In an equation for ‘g’: g (B _ _) = g A
```

In service of fixing #16043.

Towards fixing #16043.

See #16037.

Previously when switching from using a Plugin with
`RecompMaybe`/`ForceRecompile` in `pluginRecompile` to a Plugin with
`NoForceRecompile` GHC would never even consider recompiling.

However the previously active plugin could have modified the
compilation output so we should recompile.

Test Plan: validate

Reviewers: bgamari, mpickering

Subscribers: mpickering, rwbarton, carter

GHC Trac Issues: #15858

Differential Revision: https://phabricator.haskell.org/D5299

This patch collects a few improvements triggered by Trac #15696,
and fixing Trac #16029

* Stop making toCleanDmd behave specially for unlifted types.
  This special case was the cause of stupid behaviour in Trac
  #16029.  And to my joy I discovered the let/app invariant
  rendered it unnecessary.  (Maybe the special case pre-dated
  the let/app invariant.)

  Result: less special-case handling in the compiler, and
  better perf for the compiled code.

* In WwLib.mkWWstr_one, treat seqDmd like U(AAA).  It was not
  being so treated before, which again led to stupid code.

* Update and improve Notes

There are .stderr test wibbles because we get slightly different
strictness signatures for an argumment of unlifted type:
    <L,U> rather than <S,U>        for Int#
    <S,U> rather than <S(S),U(U)>  for Int

See #16035.

See #16035.

While the test is in principle applicable to many platforms, the current
implementation requires readelf, which we can only assume is present on
ELF-based platforms (e.g. Linux).

See Trac #703.