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<h3>
Ryan Scott pushed to branch wip/T18191
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/2dff814158e08aed53036bf6ebd7c3c8394af438">2dff8141</a></strong>
<div>
<span>by Ryan Scott</span>
<i>at 2020-06-05T14:21:24-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Simplify bindLHsTyVarBndrs and bindHsQTyVars
Both `bindLHsTyVarBndrs` and `bindHsQTyVars` take two separate
`Maybe` arguments, which I find terribly confusing. Thankfully, it's
possible to remove one `Maybe` argument from each of these functions,
which this patch accomplishes:
* `bindHsQTyVars` takes a `Maybe SDoc` argument, which is `Just` if
GHC should warn about any of the quantified type variables going
unused. However, every call site uses `Nothing` in practice. This
makes sense, since it doesn't really make sense to warn about
unused type variables bound by an `LHsQTyVars`. For instance, you
wouldn't warn about the `a` in `data Proxy a = Proxy` going unused.
As a result, I simply remove this `Maybe SDoc` argument altogether.
* `bindLHsTyVarBndrs` also takes a `Maybe SDoc` argument for the same
reasons that `bindHsQTyVars` took one. To make things more
confusing, however, `bindLHsTyVarBndrs` also takes a separate
`HsDocContext` argument, which is pretty-printed (to an `SDoc`) in
warnings and error messages.
In practice, the `Maybe SDoc` and the `HsDocContext` often contain
the same text. See the call sites for `bindLHsTyVarBndrs` in
`rnFamInstEqn` and `rnConDecl`, for instance. There are only a
handful of call sites where the text differs between the
`Maybe SDoc` and `HsDocContext` arguments:
* In `rnHsRuleDecl`, where the `Maybe SDoc` says "`In the rule`"
and the `HsDocContext` says "`In the transformation rule`".
* In `rnHsTyKi`/`rn_ty`, where the `Maybe SDoc` says
"`In the type`" but the `HsDocContext` is inhereted from the
surrounding context (e.g., if `rnHsTyKi` were called on a
top-level type signature, the `HsDocContext` would be
"`In the type signature`" instead)
In both cases, warnings/error messages arguably _improve_ by
unifying making the `Maybe SDoc`'s text match that of the
`HsDocContext`. As a result, I decided to remove the `Maybe SDoc`
argument to `bindLHsTyVarBndrs` entirely and simply reuse the text
from the `HsDocContext`. (I decided to change the phrase
"transformation rule" to "rewrite rule" while I was in the area.)
The `Maybe SDoc` argument has one other purpose: signaling when to
emit "`Unused quantified type variable`" warnings. To recover this
functionality, I replaced the `Maybe SDoc` argument with a
boolean-like `WarnUnusedForalls` argument. The only
`bindLHsTyVarBndrs` call site that chooses _not_ to emit these
warnings in `bindHsQTyVars`.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/e372331b3212e5d8eddfa6f8d2c3840b7e95c2b3">e372331b</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2020-06-07T08:46:41-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">hadrian: Add missing deriveConstants dependency on ghcplatform.h
deriveConstants wants to compile C sources which #include PosixSource.h,
which itself #includes ghcplatform.h. Make sure that Hadrian knows
about this dependency.
Fixes #18290.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/b022051a50d30e39d86ee21e565e899e7e98255f">b022051a</a></strong>
<div>
<span>by Moritz Angermann</span>
<i>at 2020-06-07T08:46:42-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">ghc-prim needs to depend on libc and libm
libm is just an empty shell on musl, and all the math functions are contained in
libc.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/6dae65484f9552239652f743e2303fa17aae953b">6dae6548</a></strong>
<div>
<span>by Moritz Angermann</span>
<i>at 2020-06-07T08:46:42-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Disable DLL loading if without system linker
Some platforms (musl, aarch64) do not have a working dynamic linker
implemented in the libc, even though we might see dlopen. It will
ultimately just return that this is not supported. Hence we'll add
a flag to the compiler to flat our disable loading dlls. This is
needed as we will otherwise try to load the shared library even
if this will subsequently fail. At that point we have given up
looking for static options though.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/4a158ffc4e0ac250897aefaf6caf03eb5f688182">4a158ffc</a></strong>
<div>
<span>by Moritz Angermann</span>
<i>at 2020-06-07T08:46:43-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Range is actually +/-2^32, not +/-2^31
See also: https://static.docs.arm.com/ihi0056/g/aaelf64.pdf
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/f1bfb806683b3092fc5ead84e7ecff928c55fbc4">f1bfb806</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2020-06-07T10:49:30-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">OccurAnal: Avoid exponential behavior due to where clauses
Previously the `Var` case of `occAnalApp` could in some cases (namely
in the case of `runRW#` applications) call `occAnalRhs` two. In the case
of nested `runRW#`s this results in exponential complexity. In some
cases the compilation time that resulted would be very long indeed
(see #18296).
Fixes #18296.
Metric Decrease:
T9961
T12150
T12234
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/102458850d1340f9f638d67f91e568c3d7821cef">10245885</a></strong>
<div>
<span>by Ryan Scott</span>
<i>at 2020-06-08T10:18:48-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Make GADT constructors adhere to the forall-or-nothing rule properly
Issue #18191 revealed that the types of GADT constructors don't quite
adhere to the `forall`-or-nothing rule. This patch serves to clean up
this sad state of affairs somewhat. The main change is not in the
code itself, but in the documentation, as this patch introduces two
sections to the GHC User's Guide:
* A "Formal syntax for GADTs" section that presents a BNF-style
grammar for what is and isn't allowed in GADT constructor types.
This mostly exists to codify GHC's existing behavior, but it also
imposes a new restriction that addresses #18191: the outermost
`forall` and/or context in a GADT constructor is not allowed to be
surrounded by parentheses. Doing so would make these
`forall`s/contexts nested, and GADTs do not support nested
`forall`s/contexts at present.
* A "`forall`-or-nothing rule" section that describes exactly what
the `forall`-or-nothing rule is all about. Surprisingly, there was
no mention of this anywhere in the User's Guide up until now!
To adhere the new specification in the "Formal syntax for GADTs"
section of the User's Guide, the following code changes were made:
* A new function, `GHC.Hs.Type.splitLHsGADTPrefixTy`, was introduced.
This is very much like `splitLHsSigmaTy`, except that it avoids
splitting apart any parentheses, which can be syntactically
significant for GADT types. See
`Note [No nested foralls or contexts in GADT constructors]` in
`GHC.Hs.Type`.
* `ConDeclGADTPrefixPs`, an extension constructor for `XConDecl`, was
introduced so that `GHC.Parser.PostProcess.mkGadtDecl` can return
it when given a prefix GADT constructor. Unlike `ConDeclGADT`,
`ConDeclGADTPrefixPs` does not split the GADT type into its argument
and result types, as this cannot be done until after the type is
renamed (see `Note [GADT abstract syntax]` in `GHC.Hs.Decls` for why
this is the case).
* `GHC.Renamer.Module.rnConDecl` now has an additional case for
`ConDeclGADTPrefixPs` that (1) splits apart the full `LHsType` into
its `forall`s, context, argument types, and result type, and
(2) checks for nested `forall`s/contexts. Step (2) used to be
performed the typechecker (in `GHC.Tc.TyCl.badDataConTyCon`) rather
than the renamer, but now the relevant code from the typechecker
can simply be deleted.
One nice side effect of this change is that we are able to give a
more accurate error message for GADT constructors that use visible
dependent quantification (e.g., `MkFoo :: forall a -> a -> Foo a`),
which improves the stderr in the `T16326_Fail6` test case.
Fixes #18191. Bumps the Haddock submodule.
</pre>
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<a href="#182d6a315e784018aa9c8b2ad736036b97bd5d48">
compiler/GHC/Core.hs
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<a href="#36a42448a83a9d1f6df8475f03ead2eed199dd8e">
compiler/GHC/Core/Lint.hs
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<a href="#bac3d5159a5688007de3aa3f5c4e50569677b347">
compiler/GHC/Core/Opt/OccurAnal.hs
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<a href="#f168a93cde5e2aec2441d6331dfe500172df4af3">
compiler/GHC/Core/Opt/Simplify.hs
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compiler/GHC/Core/Rules.hs
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compiler/GHC/Driver/Types.hs
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compiler/GHC/Hs/Decls.hs
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compiler/GHC/Hs/Instances.hs
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compiler/GHC/Hs/Type.hs
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compiler/GHC/Hs/Utils.hs
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compiler/GHC/HsToCore.hs
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compiler/GHC/Parser.y
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compiler/GHC/Parser/PostProcess.hs
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<a href="#13755bdc5d6c6b4c6f31604eb0da778521355795">
compiler/GHC/Parser/PostProcess/Haddock.hs
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compiler/GHC/Rename/HsType.hs
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compiler/GHC/Rename/Module.hs
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compiler/GHC/Rename/Utils.hs
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compiler/GHC/Runtime/Linker.hs
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compiler/GHC/Tc/Gen/Rule.hs
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compiler/GHC/Tc/TyCl.hs
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compiler/GHC/ThToHs.hs
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compiler/ghc.cabal.in
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<a href="#b421960e854c6cfa1e4ca830bd6a5fc6eef91168">
docs/users_guide/8.12.1-notes.rst
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hadrian/src/Rules/Generate.hs
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libraries/ghc-prim/ghc-prim.cabal
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<a href="#d2de72b871f7cea8f5a3fe27d5842227332f62ae">
rts/linker/elf_reloc_aarch64.c
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<a href="#bda6fd73ee46adb428d2f370a800d75d8870285b">
testsuite/tests/dependent/should_fail/T16326_Fail10.stderr
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testsuite/tests/dependent/should_fail/T16326_Fail6.stderr
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<h5>The diff was not included because it is too large.</h5>
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