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<h3>
Simon Peyton Jones pushed to branch wip/T17775
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/7bfe9ac514e18c0b0e24ff55230fe98ec9db894c">7bfe9ac5</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2020-05-03T04:41:33-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">rts: Enable tracing of nonmoving heap census with -ln
Previously this was not easily available to the user. Fix this.
Non-moving collection lifecycle events are now reported with -lg.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/c560dd07f506810eaabae2f582491138aa224819">c560dd07</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2020-05-03T04:41:33-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">users guide: Move eventlog documentation users guide
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/02543d5ef9bd7a910fc9fece895780583ab9635a">02543d5e</a></strong>
<div>
<span>by Ben Gamari</span>
<i>at 2020-05-03T04:41:33-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">users guide: Add documentation for non-moving GC events
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/b465dd4500beffe919e8b8dcd075008399fbf446">b465dd45</a></strong>
<div>
<span>by Alexis King</span>
<i>at 2020-05-03T04:42:12-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Flatten nested casts in the simple optimizer
Normally, we aren’t supposed to generated any nested casts, since mkCast
takes care to flatten them, but the simple optimizer didn’t use mkCast,
so they could show up after inlining. This isn’t really a problem, since
the simplifier will clean them up immediately anyway, but it can clutter
the -ddump-ds output, and it’s an extremely easy fix.
closes #18112
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/8bdc03d61cb7a2f96887c86bd0b253f7c108fcde">8bdc03d6</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-05-04T01:56:59-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Don't return a panic in tcNestedSplice
In GHC.Tc.Gen.Splice.tcNestedSplice we were returning a
typechecked expression of "panic". That is usually OK, because
the result is discarded. But it happens that tcApp now looks at
the typechecked expression, trivially, to ask if it is tagToEnum.
So being bottom is bad.
Moreover a debug-trace might print it out.
So better to return a civilised expression, even though it is
usually discarded.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/0bf640b19d7a7ad0800152752a71c1dd4e6c696d">0bf640b1</a></strong>
<div>
<span>by Baldur Blöndal</span>
<i>at 2020-05-04T01:57:36-04:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Don't require parentheses around via type (`-XDerivingVia'). Fixes #18130".
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/26aedf3d08fefbd722537e889b2029cb5ee4ce82">26aedf3d</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-05-04T11:18:15+01:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Simple subsumption
This patch simplifies GHC to use simple subsumption.
Ticket #17775
Implements GHC proposal #287
https://github.com/ghc-proposals/ghc-proposals/blob/master/
proposals/0287-simplify-subsumption.rst
All the motivation is described there; I will not repeat it here.
The implementation payload:
* tcSubType and friends become noticably simpler, because it no
longer uses eta-expansion when checking subsumption.
* No deeplyInstantiate or deeplySkolemise
That in turn means that some tests fail, by design; they can all
be fixed by eta expansion. There is a list of such changes below.
Implementing the patch led me into a variety of sticky corners, so
the patch includes several othe changes, some quite significant:
* I made String wired-in, so that
"foo" :: String rather than
"foo" :: [Char]
This improves error messages, and fixes #15679
* isTauTy: was replying True for (Show a => a ->a), which is utterly
bogus. Fixed.
* The pattern match checker relies on knowing about in-scope equality
constraints, andd adds them to the desugarer's environment using
addTyCsDs. But the co_fn in a FunBind was missed, and for some reason
simple-subsumption ends up with dictionaries there. So I added a
call to addTyCsDs. This is really part of #18049.
* I moved the ic_telescope field out of Implication and into
ForAllSkol instead. This is a nice win; just expresses the code
much better.
* There was a bug in GHC.Tc.TyCl.Instance.tcDataFamInstHeader.
We called checkDataKindSig inside tc_kind_sig, /before/
solveEqualities and zonking. Obviously wrong, easily fixed.
* solveLocalEqualitiesX: there was a whole mess in here, around
failing fast enough. I discovered a bad latent bug where we
could successfully kind-check a type signature, and use it,
but have unsolved constraints that could fill in coercion
holes in that signature -- aargh.
It's all explained in Note [Failure in local type signatures]
in GHC.Tc.Solver. Much better now.
* I fixed a serious bug in anonymous type holes. IN
f :: Int -> (forall a. a -> _) -> Int
that "_" should be a unification variable at the /outer/
level; it cannot be instantiated to 'a'. This was plain
wrong. New fields mode_lvl and mode_holes in TcTyMode,
and auxiliary data type GHC.Tc.Gen.HsType.HoleMode.
This fixes #16292, but makes no progress towards the more
ambitious #16082
* I got sucked into an enormous refactoring of the reporting of
equality errors in GHC.Tc.Errors, especially in
mkEqErr1
mkTyVarEqErr
misMatchMsg
misMatchMsgOrCND
In particular, the very tricky mkExpectedActualMsg function
is gone.
It took me a full day. But the result is far easier to understand.
(Still not easy!) This led to various minor improvements in error
output, and an enormous number of test-case error wibbles.
One particular point: for occurs-check errors I now just say
Can't match 'a' against '[a]'
rather than using the intimidating language of "occurs check".
* Pretty-printing AbsBinds
Tests review
* Eta expansions
T11305: one eta expansion
T12082: one eta expansion (undefined)
T13585a: one eta expansion
T3102: one eta expansion
T3692: two eta expansions (tricky)
T2239: two eta expansions
T16473: one eta
determ004: two eta expansions (undefined)
annfail06: two eta (undefined)
T17923: four eta expansions (a strange program indeed!)
tcrun035: one eta expansion
* Ambiguity check at higher rank. Now that we have simple
subsumption, a type like
f :: (forall a. Eq a => Int) -> Int
is no longer ambiguous, because we could write
g :: (forall a. Eq a => Int) -> Int
g = f
and it'd typecheck just fine. But f's type is a bit
suspicious, and we might want to consider making the
ambiguity check do a check on each sub-term. Meanwhile,
these tests are accepted, whereas they were previously
rejected as ambiguous:
T7220a
T15438
T10503
T9222
* Some more interesting error message wibbles
T13381: Fine: one error (Int ~ Exp Int)
rather than two (Int ~ Exp Int, Exp Int ~ Int)
T9834: Small change in error (improvement)
T10619: Improved
T2414: Small change, due to order of unification, fine
T2534: A very simple case in which a change of unification order
means we get tow unsolved constraints instead of one
tc211: bizarre impredicative tests; just accept this for now
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/a6b1ee0890b0e791c464312b2db8920868cd4b0b">a6b1ee08</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-05-04T11:18:16+01:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Wibbles
Especially make major improvement to hsWrapDictBinders
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/3310af0cbc2d212fc2d53a6da0d9d4396ed8885b">3310af0c</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-05-04T11:18:16+01:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Wibbles
esp to tcPolyCheck
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/52089110ad281e7a85731c5c20c945f4de6d1ef2">52089110</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-05-04T11:18:16+01:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Wibbles
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/54d93222af0a4dbcadce37088fbf291e84179764">54d93222</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-05-04T11:18:16+01:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Wibbles
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/188205d687bac490ed8bd7a038569aca15c25a68">188205d6</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-05-04T12:01:25+01:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Wibbles (dynamic-paper ticks)
</pre>
</li>
</ul>
<h4>23 changed files:</h4>
<ul>
<li class="file-stats">
<a href="#0887cf39c5cdf9cf8d6758f410d7dab3023c0d77">
compiler/GHC/Builtin/Names.hs
</a>
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<li class="file-stats">
<a href="#377cfd14c1f92357465df995ec6537b074051322">
compiler/GHC/Builtin/Types.hs
</a>
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<li class="file-stats">
<a href="#783e5dae6e86931f06700fc088fb7d48c8a07386">
compiler/GHC/Core/Coercion.hs
</a>
</li>
<li class="file-stats">
<a href="#11ffe98a94d798427bc600e4fcfe899407536346">
compiler/GHC/Core/SimpleOpt.hs
</a>
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<li class="file-stats">
<a href="#84c9d3ba34173297e7d7747e02caa2e004b164fc">
compiler/GHC/Core/Type.hs
</a>
</li>
<li class="file-stats">
<a href="#9a679a2680ef6061397f1987091ea9f96ffe095d">
compiler/GHC/Driver/Main.hs
</a>
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<li class="file-stats">
<a href="#65ca06d51797ebf672a62bde6c00bcb9444e1425">
compiler/GHC/Hs/Binds.hs
</a>
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<li class="file-stats">
<a href="#8cd3d37b8a77c01a0e798e67591fc3ea9c34c9ec">
compiler/GHC/Hs/Types.hs
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<li class="file-stats">
<a href="#65e2067fbb7377818b6cadff0531f44029499948">
compiler/GHC/HsToCore/Binds.hs
</a>
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<li class="file-stats">
<a href="#ac0a6473a902628a18b3a470122e5cc1ce09de14">
compiler/GHC/HsToCore/PmCheck.hs
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<li class="file-stats">
<a href="#7d51edda4fa76a202cce0bca672ef300249ba8ea">
compiler/GHC/Iface/Load.hs
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<li class="file-stats">
<a href="#bf951467d4a9aa443cb109cb4c84a2891945649b">
compiler/GHC/Parser.y
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<li class="file-stats">
<a href="#892acbb198a9095c917740d3c1297b56df4e3b7e">
compiler/GHC/Rename/HsType.hs
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<li class="file-stats">
<a href="#16b273b96a1c03d4261e2ac6de4cc456ba2dd014">
compiler/GHC/Rename/Splice.hs
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<li class="file-stats">
<a href="#e4b9d5e9d2de37561bfd06a2c97a5c924a1bab76">
compiler/GHC/Tc/Errors.hs
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<li class="file-stats">
<a href="#897218b3e24728ae9e5b0329b949493f1ede80fb">
compiler/GHC/Tc/Errors/Hole.hs
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<li class="file-stats">
<a href="#71fa5eb3ba70e1d3a6181a226c2c227d42f1eb7d">
compiler/GHC/Tc/Gen/Arrow.hs
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<li class="file-stats">
<a href="#83f745d921da7adb739e81f83e1c07e723e4a789">
compiler/GHC/Tc/Gen/Bind.hs
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<li class="file-stats">
<a href="#b18f1cc437ab64ccd37a7cae3b8c3f9071aef45e">
compiler/GHC/Tc/Gen/Default.hs
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<li class="file-stats">
<a href="#902811828741e6bcd64702935bbb54edbbd070ef">
compiler/GHC/Tc/Gen/Expr.hs
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<li class="file-stats">
<a href="#8dec347fbe40358b852d7b50ace1e4d62b9b6660">
compiler/GHC/Tc/Gen/Expr.hs-boot
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<li class="file-stats">
<a href="#08a3d553a8ca7a753d77697815b63cd85e7dfbd6">
compiler/GHC/Tc/Gen/Foreign.hs
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<li class="file-stats">
<a href="#9355bef855426caf5f526925edf351b20f9a86c4">
compiler/GHC/Tc/Gen/HsType.hs
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</ul>
<h5>The diff was not included because it is too large.</h5>
</div>
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