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This patch removes the following defaulting of type variables
in type and data families:
- type variables of kind RuntimeRep defaulting to LiftedRep
- type variables of kind Levity defaulting to Lifted
- type variables of kind Multiplicity defaulting to Many
It does this by passing "defaulting options" to the `defaultTyVars`
function; when calling from `tcTyFamInstEqnGuts` or
`tcDataFamInstHeader` we pass options that avoid defaulting.
This avoids wildcards being defaulted, which caused type families
to unexpectedly fail to reduce.
Note that kind defaulting, applicable only with -XNoPolyKinds,
is not changed by this patch.
Fixes #17536
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Metric Increase:
T12227
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PHASE 1: we never rewrite Concrete# evidence.
This patch migrates all the representation polymorphism checks to
the typechecker, using a new constraint form
Concrete# :: forall k. k -> TupleRep '[]
Whenever a type `ty` must be representation-polymorphic
(e.g. it is the type of an argument to a function), we emit a new
`Concrete# ty` Wanted constraint. If this constraint goes
unsolved, we report a representation-polymorphism error to the user.
The 'FRROrigin' datatype keeps track of the context of the
representation-polymorphism check, for more informative error messages.
This paves the way for further improvements, such as
allowing type families in RuntimeReps and improving the soundness
of typed Template Haskell. This is left as future work (PHASE 2).
fixes #17907 #20277 #20330 #20423 #20426
updates haddock submodule
-------------------------
Metric Decrease:
T5642
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