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Use an (Raw)PkgQual datatype instead of `Maybe FastString` to represent
package imports. Factorize the code that renames RawPkgQual into PkgQual
in function `rnPkgQual`. Renaming consists in checking if the FastString
is the magic "this" keyword, the home-unit unit-id or something else.
Bump haddock submodule
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Before this patch Integer and Natural literals were desugared into "real"
Core in Core prep. Now we desugar them directly into their final ConApp
form in HsToCore. We only keep the double representation for BigNat#
(literals larger than a machine Word/Int) which are still desugared in
Core prep.
Using the final form directly allows case-of-known-constructor to fire
for bignum literals, fixing #20245.
Slight increase (+2.3) in T4801 which is a pathological case with
Integer literals.
Metric Increase:
T4801
T11545
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Type-checking plugins can now directly rewrite type-families.
The TcPlugin record is given a new field, tcPluginRewrite.
The plugin specifies how to rewrite certain type-families with a value
of type `UniqFM TyCon TcPluginRewriter`, where:
type TcPluginRewriter
= RewriteEnv -- Rewriter environment
-> [Ct] -- Givens
-> [TcType] -- type family arguments
-> TcPluginM TcPluginRewriteResult
data TcPluginRewriteResult
= TcPluginNoRewrite
| TcPluginRewriteTo
{ tcPluginRewriteTo :: Reduction
, tcRewriterNewWanteds :: [Ct]
}
When rewriting an exactly-saturated type-family application,
GHC will first query type-checking plugins for possible rewritings
before proceeding.
Includes some changes to the TcPlugin API, e.g. removal
of the EvBindsVar parameter to the TcPluginM monad.
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We define Reduction = Reduction Coercion !Type.
A reduction of the form 'Reduction co new_ty' witnesses an
equality ty ~co~> new_ty.
That is, the rewriting happens left-to-right: the right-hand-side
type of the coercion is the rewritten type, and the left-hand-side
type the original type.
Sticking to this convention makes the codebase more consistent,
helping to avoid certain applications of SymCo.
This replaces the parts of the codebase which represented reductions as
pairs, (Coercion,Type) or (Type,Coercion).
Reduction being strict in the Type argument improves performance
in some programs that rewrite many type families (such as T9872).
Fixes #20161
-------------------------
Metric Decrease:
T5321Fun
T9872a
T9872b
T9872c
T9872d
-------------------------
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This patch redesigns the flattener to simplify type family applications
directly instead of using flattening meta-variables and skolems. The key new
innovation is the CanEqLHS type and the new CEqCan constraint (Ct). A CanEqLHS
is either a type variable or exactly-saturated type family application; either
can now be rewritten using a CEqCan constraint in the inert set.
Because the flattener no longer reduces all type family applications to
variables, there was some performance degradation if a lengthy type family
application is now flattened over and over (not making progress). To
compensate, this patch contains some extra optimizations in the flattener,
leading to a number of performance improvements.
Close #18875.
Close #18910.
There are many extra parts of the compiler that had to be affected in writing
this patch:
* The family-application cache (formerly the flat-cache) sometimes stores
coercions built from Given inerts. When these inerts get kicked out, we must
kick out from the cache as well. (This was, I believe, true previously, but
somehow never caused trouble.) Kicking out from the cache requires adding a
filterTM function to TrieMap.
* This patch obviates the need to distinguish "blocking" coercion holes from
non-blocking ones (which, previously, arose from CFunEqCans). There is thus
some simplification around coercion holes.
* Extra commentary throughout parts of the code I read through, to preserve
the knowledge I gained while working.
* A change in the pure unifier around unifying skolems with other types.
Unifying a skolem now leads to SurelyApart, not MaybeApart, as documented
in Note [Binding when looking up instances] in GHC.Core.InstEnv.
* Some more use of MCoercion where appropriate.
* Previously, class-instance lookup automatically noticed that e.g. C Int was
a "unifier" to a target [W] C (F Bool), because the F Bool was flattened to
a variable. Now, a little more care must be taken around checking for
unifying instances.
* Previously, tcSplitTyConApp_maybe would split (Eq a => a). This is silly,
because (=>) is not a tycon in Haskell. Fixed now, but there are some
knock-on changes in e.g. TrieMap code and in the canonicaliser.
* New function anyFreeVarsOf{Type,Co} to check whether a free variable
satisfies a certain predicate.
* Type synonyms now remember whether or not they are "forgetful"; a forgetful
synonym drops at least one argument. This is useful when flattening; see
flattenView.
* The pattern-match completeness checker invokes the solver. This invocation
might need to look through newtypes when checking representational equality.
Thus, the desugarer needs to keep track of the in-scope variables to know
what newtype constructors are in scope. I bet this bug was around before but
never noticed.
* Extra-constraints wildcards are no longer simplified before printing.
See Note [Do not simplify ConstraintHoles] in GHC.Tc.Solver.
* Whether or not there are Given equalities has become slightly subtler.
See the new HasGivenEqs datatype.
* Note [Type variable cycles in Givens] in GHC.Tc.Solver.Canonical
explains a significant new wrinkle in the new approach.
* See Note [What might match later?] in GHC.Tc.Solver.Interact, which
explains the fix to #18910.
* The inert_count field of InertCans wasn't actually used, so I removed
it.
Though I (Richard) did the implementation, Simon PJ was very involved
in design and review.
This updates the Haddock submodule to avoid #18932 by adding
a type signature.
-------------------------
Metric Decrease:
T12227
T5030
T9872a
T9872b
T9872c
Metric Increase:
T9872d
-------------------------
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I was working on making DynFlags stateless (#17957), especially by
storing loaded plugins into HscEnv instead of DynFlags. It turned out to
be complicated because HscEnv is in GHC.Driver.Types but LoadedPlugin
isn't: it is in GHC.Driver.Plugins which depends on GHC.Driver.Types. I
didn't feel like introducing yet another hs-boot file to break the loop.
Additionally I remember that while we introduced the module hierarchy
(#13009) we talked about splitting GHC.Driver.Types because it contained
various unrelated types and functions, but we never executed. I didn't
feel like making GHC.Driver.Types bigger with more unrelated Plugins
related types, so finally I bit the bullet and split GHC.Driver.Types.
As a consequence this patch moves a lot of things. I've tried to put
them into appropriate modules but nothing is set in stone.
Several other things moved to avoid loops.
* Removed Binary instances from GHC.Utils.Binary for random compiler
things
* Moved Typeable Binary instances into GHC.Utils.Binary.Typeable: they
import a lot of things that users of GHC.Utils.Binary don't want to
depend on.
* put everything related to Units/Modules under GHC.Unit:
GHC.Unit.Finder, GHC.Unit.Module.{ModGuts,ModIface,Deps,etc.}
* Created several modules under GHC.Types: GHC.Types.Fixity, SourceText,
etc.
* Split GHC.Utils.Error (into GHC.Types.Error)
* Finally removed GHC.Driver.Types
Note that this patch doesn't put loaded plugins into HscEnv. It's left
for another patch.
Bump haddock submodule
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Introduce GHC.Unit.* hierarchy for everything concerning units, packages
and modules.
Update Haddock submodule
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Update Haddock submodule
Metric Increase:
haddock.compiler
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Update Haddock submodule
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