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As noted in #18726, this regularly breaks. Let's test it.

Note that we don't actually perform a build of GHC itself; we merely
test that the Hadrian executable builds and works (by invoking `hadrian
--version`).

This commit removes the separate kind 'Nat' and enables promotion
of type 'Natural' for using as type literal.
It partially solves #10776

Now the following code will be successfully typechecked:
    data C = MkC Natural
    type CC = MkC 1

Before this change we had to create the separate type for promotion
    data C = MkC Natural
    data CP = MkCP Nat
    type CC = MkCP 1

But CP is uninhabited in terms.

For backward compatibility type synonym `Nat` has been made:
    type Nat = Natural

The user's documentation and tests have been updated.
The haddock submodule also have been updated.

The HomeUnitId is only used by the Cmm parser and this one has access to
the DynFlags, so it can grab the UnitId of the HomeUnit from them.

Bump haddock submodule

Metric Decrease:
    Naperian
    T10421
    T10421a
    T10547
    T12150
    T12234
    T12425
    T13035
    T18140
    T18304
    T5837
    T6048
    T13253-spj
    T18282
    T18223
    T3064
    T9961
Metric Increase
    T13701

HFSKJH

Make demand analysis usable without having to provide DynFlags.

Before this patch, referring to a data constructor in a term-level
context led to a scoping error:

    ghci> id Int
    <interactive>:1:4: error: Data constructor not in scope: Int

After this patch, the renamer falls back to the type namespace
and successfully finds the Int. It is then rejected in the type
checker with a more useful error message:

    <interactive>:1:4: error:
    • Illegal term-level use of the type constructor ‘Int’
        imported from ‘Prelude’ (and originally defined in ‘GHC.Types’)
    • In the first argument of ‘id’, namely ‘Int’
      In the expression: id Int

We also do this for type variables.

Instead of recreating the HomeUnit from the DynFlags every time we need
it, we store it in the HscEnv.

!3798 added documentation and semantics for the flags,
but not parsing.

Firstly this improves code clarity.

But it also has performance benefits as we no longer
go through the name of the TyCon to get at it's unique.

In order to make this work the recursion check for TyCon
has been moved into it's own module in order to avoid import
cycles.

This should fix #18774.

This fixes a long-standing bug in the desugaring of record
updates for data families, when the latter involves a GADT. It's
all explained in Note [Update for GADTs] in GHC.HsToCore.Expr.

Building the correct cast is surprisingly tricky, as that Note
explains.

Fixes #18809.  The test case (in indexed-types/should_compile/T18809)
contains several examples that exercise the dark corners.

Previously the make build system's source distribution rules neglected
to include Hadrian's sources.

Fixes #18794.

A cleanup in 7f418acf accidentally discarded some parens in
ConDeclGADT.

Make sure these stay in the AST in a usable format.

Also ensure the AnnLolly does not get lost in a GADT.

Previously we only matched on *variables* whose unfoldings were a ConApp
of the form `IS lit#` or `NS lit##`. But we forgot to match on the
ConApp directly... As a consequence, constant folding only worked after
the FloatOut pass which creates bindings for most sub-expressions. With
this patch, matching on bignums works even with -O0 (see bignumMatch
test).

We now seem to use -Werror there. Which caused some long standing
warnings to become errors.

I applied changes to remove the warnings allowing the testsuite to
run on windows as well.

Replace options like collect_stats(['peak_megabytes_allocated'],4) with
collect_runtime_residency(4) and so forth. Reason being that the later
also supplies some default RTS arguments which make sure residency does
not fluctuate too much.

The new flags mean we get new (hopefully more accurate) baselines so
accept the stat changes.

-------------------------
Metric Decrease:
     T4029
     T4334
     T7850
Metric Increase:
     T13218
     T7436
-------------------------

Fixes #17919.

Tracking: #18641

Some RTS ways are exposed via settings (ghcThreaded, ghcDebugged) but
not all. It's simpler if the RTS exposes them all itself.

On windows the stack has to be allocated 4k at a time, otherwise we get
a segfault. This is done by using a helper ___chkstk_ms that is provided
by libgcc. The Haskell side already knows how to handle this but we need
to do the same from STG. Previously we would drop the stack in StgRun
but would only make it valid whenever the scheduler loop ran.

This approach was fundamentally broken in that it falls apart when you
take a signal from the OS. We see it less often because you initially
get allocated a 1MB stack block which you have to blow past first.

Concretely this means we must always keep the stack valid.

Fixes #18601.

Updates containers submodule.

In Cmm we can only have real units identified with an UnitId.  Other
units (on-the-fly instantiated units and holes) are only used in
type-checking backpack sessions that don't produce Cmm.

* Include funTyCon in exposedPrimTyCons.
  Every single place using exposedPrimTyCons was adding funTyCon
  manually.
* Remove unused synTyConResKind and ieLWrappedName
* Add recordSelectorTyCon_maybe
* In exprType, panic instead of giving a trace message and dummy output.
  This prevents #18767 reoccurring.
* Fix compilation error in fragile concprog001 test (part of #18732)

Several people have struggled with metric change annotations
in their commit messages not being recognized due to the fact that
GitLab's job log inserts a space at the beginning of each line. Teach
the regular expression to accept this whitespace.

Fixes #18800.

When linear types are disabled, HsUnrestrictedArrow is treated as
HslinearArrow.

Move this adjustment into the type checking phase, so that the parsed
source accurately represents the source as parsed.

Closes #18791