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Plug many variance holes (in higher-kinded types, refined types and private inner classes) #8545

Merged
merged 4 commits into from Mar 19, 2020
Merged

Plug many variance holes (in higher-kinded types, refined types and private inner classes) #8545

merged 4 commits into from Mar 19, 2020

Commits on Feb 8, 2020

  1. Plug many variance holes (pos and neg) 

    The variance checks root in `RefChecks` for `TypeTree`s is modified
to check only the variance of `PolyType`s (this includes type lambdas).
Checking the definition of the `PolyType`s' owners is not correct,
because `relativeVariance` doesn't work for types in arbitrary position.

To check the variance of `PolyType`s we introduce a new type map:
`PolyTypeVarianceMap`. This is similar to the way variance is checked
for type lambdas in dotty, where type lambdas are encoded explicitly.

We also add explicit tracking for lower bounds of `PolyType`s.
For a type parameter of a `PolyType`, the variance should not be
flipped (or equivalently, flipped twice) in the lower bound.
This applies to both `ValidateVarianceMap` and `PolyTypeVarianceMap`.
It fixes variance bugs for types appering in the bounds of HKTs.

Finally, we don't skip local definitions entirely (this is unsound),
but instead cutoff `relativeVariance` at local boundaries.
    @joroKr21
    joroKr21 committed Feb 8, 2020
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  2. Add missing pattern match case in varianceInType

    @joroKr21
    joroKr21 committed Feb 8, 2020
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  3. Remove variance check for escaping locals

    @joroKr21
    joroKr21 committed Feb 8, 2020
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  4. Variances: replace lowerBoundStack with a single flag 

    Add documentation to the two different variance validation methods:
`validateDefinition` and `validateVarianceOfPolyTypesIn`.
    @joroKr21
    joroKr21 committed Feb 8, 2020
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