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<h3>
Ben Gamari pushed to branch wip/backports
at <a href="https://gitlab.haskell.org/ghc/ghc">Glasgow Haskell Compiler / GHC</a>
</h3>
<h4>
Commits:
</h4>
<ul>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/8ec9a77dc1539b7442ae140956e92204983b3cee">8ec9a77d</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2020-05-30T10:31:04-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">rts/CNF: Fix fixup comparison function
Previously we would implicitly convert the difference between two words
to an int, resulting in an integer overflow on 64-bit machines.
Fixes #16992
(cherry picked from commit cf4f1e2f78840d25b132de55bce1e02256334ace)
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/90aa3c33298deed3aa17c9b03bde2f2c4f823c79">90aa3c33</a></strong>
<div>
<span>by Ryan Scott</span>
<i>at 2020-05-30T10:33:49-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Make boxed 1-tuples have known keys
Unlike other tuples, which use special syntax and are "known" by way
of a special `isBuiltInOcc_maybe` code path, boxed 1-tuples do not
use special syntax. Therefore, in order to make sure that the
internals of GHC are aware of the `data Unit a = Unit a` definition
in `GHC.Tuple`, we give `Unit` known keys. For the full details, see
`Note [One-tuples] (Wrinkle: Make boxed one-tuple names have known keys)`
in `GHC.Builtin.Types`.
Fixes #18097.
(cherry picked from commit 518a63d4d7e31e49a81ad66d5e5ccb1f790f6de9)
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/2436537ab6b1f2fd839f891e314878dbd85b7f87">2436537a</a></strong>
<div>
<span>by Ryan Scott</span>
<i>at 2020-05-30T10:38:12-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Create di_scoped_tvs for associated data family instances properly
See `Note [Associated data family instances and di_scoped_tvs]` in
`GHC.Tc.TyCl.Instance`, which explains all of the moving parts.
Fixes #18055.
(cherry picked from commit cd8409c26d4370bf2cdcd76801974e99a9adf7b0)
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/3c82e33665535f068092796af678e20f57defdb8">3c82e336</a></strong>
<div>
<span>by Sebastian Graf</span>
<i>at 2020-05-30T10:44:29-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">PmCheck: Adjust recursion depth for inhabitation test
In #17977, we ran into the reduction depth limit of the typechecker.
That was only a symptom of a much broader issue: The recursion depth
of the coverage checker for trying to instantiate strict fields in the
`nonVoid` test was far too high (100, the `defaultMaxTcBound`).
As a result, we were performing quite poorly on `T17977`.
Short of a proper termination analysis to prove emptyness of a type,
we just arbitrarily default to a much lower recursion limit of 3.
Fixes #17977.
(cherry picked from commit ed58d4fdcbc7b4fa8fbdf3d638a8d53c444ef4f2)
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/84a23093fe7bba102eb57f20f533d303b3ad7054">84a23093</a></strong>
<div>
<span>by Ryan Scott</span>
<i>at 2020-05-30T10:45:46-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Run checkNewDataCon before constraint-solving newtype constructors
Within `checkValidDataCon`, we used to run `checkValidType` on the
argument types of a newtype constructor before running
`checkNewDataCon`, which ensures that the user does not attempt
non-sensical things such as newtypes with multiple arguments or
constraints. This works out in most situations, but this falls over
on a corner case revealed in #17955:
```hs
newtype T = Coercible () T => T ()
```
`checkValidType`, among other things, peforms an ambiguity check on
the context of a data constructor, and that it turn invokes the
constraint solver. It turns out that there is a special case in the
constraint solver for representational equalities (read: `Coercible`
constraints) that causes newtypes to be unwrapped (see
`Note [Unwrap newtypes first]` in `TcCanonical`). This special case
does not know how to cope with an ill formed newtype like `T`, so
it ends up panicking.
The solution is surprisingly simple: just invoke `checkNewDataCon`
before `checkValidType` to ensure that the illicit newtype
constructor context is detected before the constraint solver can
run amok with it.
Fixes #17955.
(cherry picked from commit a0d8e92e9c9b67426aa139d6bc46363d8940f992)
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/3e31aad8751d84230013bfdcaeee68a0fc0ceffa">3e31aad8</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-05-30T10:46:54-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Improve skolemisation
This patch avoids skolemiseUnboundMetaTyVar making
up a fresh Name when it doesn't need to.
See Note [Skolemising and identity]
Improves error messsages for partial type signatures.
(cherry picked from commit d7002bccd7d131f8ee9b1ddcd83d62262622294d)
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/3c0e6d70160497d872619cd91071a839cb715017">3c0e6d70</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-05-30T10:47:03-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Improve pretty-printing for TyConBinders
In particular, show their kinds.
(cherry picked from commit fa37940cd72f82abc460f5c0a5de64dd75cee6ae)
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/99e643baf247fa5276ab4199cfd5a18e4c1d76d2">99e643ba</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-05-30T11:10:33-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Fix scoping of TyCon binders in TcTyClsDecls
This patch fixes #17566 by refactoring the way we decide the final
identity of the tyvars in the TyCons of a possibly-recursive nest
of type and class decls, possibly with associated types.
It's all laid out in
Note [Swizzling the tyvars before generaliseTcTyCon]
Main changes:
* We have to generalise each decl (with its associated types)
all at once: TcTyClsDecls.generaliseTyClDecl
* The main new work is done in TcTyClsDecls.swizzleTcTyConBndrs
* The mysterious TcHsSyn.zonkRecTyVarBndrs dies altogether
Other smaller things:
* A little refactoring, moving bindTyClTyVars from tcTyClDecl1
to tcDataDefn, tcSynRhs, etc. Clearer, reduces the number of
parameters
* Reduce the amount of swizzling required.
Specifically, bindExplicitTKBndrs_Q_Tv doesn't need
to clone a new Name for the TyVarTv, and not
cloning means that in the vasly common case,
swizzleTyConBndrs is a no-op
In detail:
Rename newTyVarTyVar --> cloneTyVarTyVar
Add newTyVarTyTyVar that doesn't clone
Use the non-cloning newTyVarTyVar in
bindExplicitTKBndrs_Q_Tv
Rename newFlexiKindedTyVarTyVar
--> cloneFlexiKindedTyVarTyVar
* Define new utility function and use it
HsDecls.familyDeclName ::
FamilyDecl (GhcPass p) -> IdP (GhcPass p)
Updates haddock submodule.
(cherry picked from commit b9605396f1f1560aea94792646b835cadcb49f45)
</pre>
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<a href="#75bfcd03f3ba9315d33104fcb0424c6bfeb4e334">
compiler/GHC/Hs/Decls.hs
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compiler/GHC/HsToCore/PmCheck/Oracle.hs
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compiler/prelude/PrelInfo.hs
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compiler/prelude/PrelNames.hs
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compiler/prelude/TysWiredIn.hs
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compiler/typecheck/TcHsSyn.hs
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compiler/typecheck/TcHsType.hs
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compiler/typecheck/TcInstDcls.hs
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compiler/typecheck/TcMType.hs
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compiler/typecheck/TcTyClsDecls.hs
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rts/sm/CNF.c
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