We no longer emit a warning when a safe module is explicitly declared as
such.

This matches GHC itself getting the target platform from there.

ghc-pkg needs to be aware of platforms so it can figure out which
subdire within the user package db to use. This is admittedly
roundabout, but maybe Cabal could use the same notion of a platform as
GHC to good affect too.

* Added Note [Quantified varaibles in partial type signatures]
  in TcRnTypes

* Kill dVarSetElemsWellScoped; it was only called in
  one function, quantifyTyVars.  I inlined it because it
  was only scopedSort . dVarSetElems

* Kill Type.tyCoVarsOfBindersWellScoped, never called.

Partial type sigs had grown hair.  tcHsParialSigType was
doing lots of unnecessary work, and tcInstSig was cloning it
unnecessarily -- and the result didn't even work: #16728.

This patch cleans it all up, described by TcHsType
  Note [Checking parital type signatures]

I basically just deleted code... but very carefully!

Some refactoring along the way

* Distinguish more explicintly between "anonymous" wildcards "_"
  and "named" wildcards "_a".  I changed the names of a number
  of functions to make this distinction much more apparent.

The patch also revealed that the code in `TcExpr`
that implements the special typing rule for `($)` was wrong.
It called `getRuntimeRep` in a situation where where was no
particular reason to suppose that the thing had kind `TYPE r`.

This caused a crash in typecheck/should_run/T10846.

The fix was easy, and actually simplifies the code in `TcExpr`
quite a bit.  Hooray.

The substition invariant relies on keeping the in-scope
set in sync, and we weren't always doing so, which means that
a DEBUG compiler crashes sometimes with an assertion failure

This patch fixes a couple more cases.  Still not validate
clean (with -DEEBUG) but closer!

After a :cd command and after setting some package flags,
GHCi unloads all loaded modules by resetting the list of targets.

This patch deletes eventually defined debugger breakpoints, before GHCi resets the target list.

The common code is factored out into the new function clearAllTargets.

Not doing this right caused #16608. We now properly trim IdInfos of
DFunIds and PatSyns.

Some further refactoring done by SPJ.

Two regression tests T16608_1 and T16608_2 added.

Fixes #16608

("Continuation BlockIds" is referenced in CmmProcPoint)

[skip ci]

mkSplitUniqSupply was lazy on the boxed char.

This caused a bunch of issues:
* The closure captured the boxed Char
* The mask was recomputed on every split of the supply.
* It also caused the allocation of MkSplitSupply to happen in it's own
(allocated) closure. The reason of which I did not further investigate.

We know force the computation of the mask inside mkSplitUniqSupply.
* This way the mask is computed at most once per UniqSupply creation.
* It allows ww to kick in, causing the closure to retain the unboxed
value.

Requesting Uniques in a loop is now faster by about 20%.

I did not check the impact on the overall compiler, but I added a test
to avoid regressions.

This guarantees that the interface file for `UserSettings` doesn't 
contain any unfoldings, ensuring that a change in it requires minimal 
rebuilds.

Fixes #16689.

Metric Increase:
    haddock.base

Updates docker images to ensure that the `time` utility is available.

Now since this is generated by the build system we should ensure that it
is properly cleaned.

[skip ci]

This #16741 out of the way this should now pass.

The previous fix, !1095, didn't work as `--show-iface` ignores
`-dsuppress-ticks`. Rework the test instead.

Before this patch, runghc would only run the GHC detection logic on Windows and
assume that it was invoked through a wrapper script on all other platforms.
This patch lifts this limitation and makes that logic work for the scenario
where someone is calling the runghc executable directly, without passing an
explicit path to GHC.

The libc output buffer wasn't being flushed, making the order
system-depedent.

Otherwise it the order out the Haskell and C output will be
system-dependent.

Previously T5423 would fail to flush the printf output buffer.
Consequently it was platform-dependent whether the C or Haskell print
output would be emitted first.

Musl wants hash-bangs on all executables.

Previously the Event enumeration produced by hsc2hs would sometimes
include a currently-unused POLLRDHUP item. This unused binding would
result in a build failure. Drop it.

Issue #15862 demonstrated examples of type constructors on which
`TcTypeable.tyConIsTypeable` would return `False`, but the `Typeable`
constraint solver in `ClsInst` (in particular, `doTyConApp`) would
try to generate `Typeable` evidence for anyway, resulting in
disaster. This incongruity was caused by the fact that `doTyConApp`
was using a weaker validity check than `tyConIsTypeable` to determine
if a type constructor warrants `Typeable` evidence or not. The
solution, perhaps unsurprisingly, is to use `tyConIsTypeable` in
`doTyConApp` instead.

To avoid import cycles between `ClsInst` and `TcTypeable`, I factored
out `tyConIsTypeable` into its own module, `TcTypeableValidity`.

Fixes #15862.

Previously there were a few cases where operations like `omit_ways`
were incorrectly passed a single way (e.g. `omit_ways('threaded2')`).
This won't work as the author expected.

As noted in #16819, this operation is racy under concurrent execution.

Previously we just tested for the threaded2 when determining whether to
skip tests which are fragile under concurrent execution. However, this
isn't the only way which is concurrent.

This updates the make and Hadrian build flavours targetting developers
to disable optimisation when building the Cabal library. Cabal tends to
tickle some very bad compiler performance cases (e.g. #16577) so
disabling optimisation here makes a sizeable impact on overall build
time.

See #16817.

This disables optimisation when building Cabal for Hadrian and
stage0 `ghc-cabal`. Cabal is performance critical in neither case nor
will any performance difference here be visible to the end-user.

See #16817.