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<h3>
Ben Gamari pushed to branch wip/T17656
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/80df2edd1b28dc211a894ab7c4faf1c8a0c92fcb">80df2edd</a></strong>
<div>
<span>by David Eichmann</span>
<i>at 2020-12-17T13:55:21-05:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">User guide minor typo
[ci skip]
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/09f2839086d43483066e45fe15bb7a0b39f8d1dc">09f28390</a></strong>
<div>
<span>by nineonine</span>
<i>at 2020-12-17T13:55:59-05:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Force module recompilation if '*' prefix was used to load modules in ghci (#8042)
Usually pre-compiled code is preferred to be loaded in ghci if available, which means
that if we try to load module with '*' prefix and compilation artifacts are available
on disc (.o and .hi files) or the source code was untouched, the driver would think
no recompilation is required. Therefore, we need to force recompilation so that desired
byte-code is generated and loaded. Forcing in this case should be ok, since this is what
happens for interpreted code anyways when reloading modules.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/b1178cbc87feb1ec9c2bf98e0ad347f99dd3f20e">b1178cbc</a></strong>
<div>
<span>by Ryan Scott</span>
<i>at 2020-12-17T13:56:35-05:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Reject dodgy scoping in associated family instance RHSes
Commit e63518f5d6a93be111f9108c0990a1162f88d615 tried to push all of the logic
of detecting out-of-scope type variables on the RHSes of associated type family
instances to `GHC.Tc.Validity` by deleting a similar check in the renamer.
Unfortunately, this commit went a little too far, as there are some corner
cases that `GHC.Tc.Validity` doesn't detect. Consider this example:
```hs
class C a where
data D a
instance forall a. C Int where
data instance D Int = MkD a
```
If this program isn't rejected by the time it reaches the typechecker, then
GHC will believe the `a` in `MkD a` is existentially quantified and accept it.
This is almost surely not what the user wants! The simplest way to reject
programs like this is to restore the old validity check in the renamer
(search for `improperly_scoped` in `rnFamEqn`).
Note that this is technically a breaking change, since the program in the
`polykinds/T9574` test case (which previously compiled) will now be rejected:
```hs
instance Funct ('KProxy :: KProxy o) where
type Codomain 'KProxy = NatTr (Proxy :: o -> *)
```
This is because the `o` on the RHS will now be rejected for being out of scope.
Luckily, this is simple to repair:
```hs
instance Funct ('KProxy :: KProxy o) where
type Codomain ('KProxy @o) = NatTr (Proxy :: o -> *)
```
All of the discussion is now a part of the revamped
`Note [Renaming associated types]` in `GHC.Rename.Module`.
A different design would be to make associated type family instances have
completely separate scoping from the parent instance declaration, much like
how associated type family default declarations work today. See the discussion
beginning at https://gitlab.haskell.org/ghc/ghc/-/issues/18021#note_265729 for
more on this point. This, however, would break even more programs that are
accepted today and likely warrants a GHC proposal before going forward. In the
meantime, this patch fixes the issue described in #18021 in the least invasive
way possible. There are programs that are accepted today that will no longer
be accepted after this patch, but they are arguably pathological programs, and
they are simple to repair.
Fixes #18021.
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/cf8ab4a6a5271c072fefb946186600baaf8b1671">cf8ab4a6</a></strong>
<div>
<span>by Tom Ellis</span>
<i>at 2020-12-17T13:57:12-05:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">submodule update: containers and stm
Needed for https://gitlab.haskell.org/ghc/ghc/-/issues/15656 as it
stops the packages triggering incomplete-uni-patterns and
incomplete-record-updates
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/df7c7faa9998f2b618eab586bb4420d6743aad18">df7c7faa</a></strong>
<div>
<span>by Richard Eisenberg</span>
<i>at 2020-12-17T13:57:48-05:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Unfortunate dirty hack to overcome #18998.
See commentary in tcCheckUsage.
Close #18998.
Test case: typecheck/should_compile/T18998
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/659fcb14937e60510e3eea4c1211ea117419905b">659fcb14</a></strong>
<div>
<span>by Sylvain Henry</span>
<i>at 2020-12-17T13:58:30-05:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Fix project version for ProjectVersionMunged (fix #19058)
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/ac5b1742f3390c95ade4ada822b000ab3e182c3f">ac5b1742</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-12-17T21:01:07-05:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Kill floatEqualities completely
This patch delivers on #17656, by entirel killing off the complex
floatEqualities mechanism. Previously, floatEqualities would float an
equality out of an implication, so that it could be solved at an outer
level. But now we simply do unification in-place, without floating the
constraint, relying on level numbers to determine untouchability.
There are a number of important new Notes:
* GHC.Tc.Utils.Unify Note [Unification preconditions]
describes the preconditions for unification, including both
skolem-escape and touchability.
* GHC.Tc.Solver.Interact Note [Solve by unification]
describes what we do when we do unify
* GHC.Tc.Solver.Monad Note [The Unification Level Flag]
describes how we control solver iteration under this new scheme
* GHC.Tc.Solver.Monad Note [Tracking Given equalities]
describes how we track when we have Given equalities
* GHC.Tc.Types.Constraint Note [HasGivenEqs]
is a new explanation of the ic_given_eqs field of an implication
A big raft of subtle Notes in Solver, concerning floatEqualities,
disappears.
Main code changes:
* GHC.Tc.Solver.floatEqualities disappears entirely
* GHC.Tc.Solver.Monad: new fields in InertCans, inert_given_eq_lvl
and inert_given_eq, updated by updateGivenEqs
See Note [Tracking Given equalities].
* In exchange for updateGivenEqa, GHC.Tc.Solver.Monad.getHasGivenEqs
is much simpler and more efficient
* I found I could kill of metaTyVarUpdateOK entirely
One test case T14683 showed a 5.1% decrease in compile-time
allocation; and T5631 was down 2.2%. Other changes were small.
Metric Decrease:
T14683
T5631
</pre>
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<a href="#b8dbb28cac2b7ba465be98a9ef055178d1b8bdec">
.gitlab/linters/check-version-number.sh
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<a href="#b8e6af642e56019828828dc679683c04afb81867">
compiler/GHC/Driver/Pipeline.hs
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compiler/GHC/Rename/Module.hs
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compiler/GHC/Tc/Errors.hs
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compiler/GHC/Tc/Gen/App.hs
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compiler/GHC/Tc/Solver.hs
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compiler/GHC/Tc/Solver/Canonical.hs
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libraries/containers
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libraries/stm
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