promoteLetDecName: Fix visibility-related bug
#586
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This is needed to bring in a fix for goldfirere/th-desugar#212, which we will use in a subsequent commit.
Previously, `promoteLetDecName` would convert every `DTyVarBndrSpec` in an outermost `forall` to an invisible argument in a promoted type family equation. This is not quite right, however, as #585 reveals: we do not want to convert _inferred_ type variable binders to invisible arguments. To do this properly, we introduce a new `tvbSpecsToBndrVis` function, which converts a list of `DTyVarBndrSpec`s to a list of `DTyVarBndrVis`es, dropping any `DTyVarBndrSpec`s with an `InferredSpec` in the process. We then use `tvbSpecsToBndrVis` in `promoteLetDecName`, which neatly fixes #585.
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Previously,
promoteLetDecNamewould convert everyDTyVarBndrSpecin an outermostforallto an invisible argument in a promoted type family equation. This is not quite right, however, as #585 reveals: we do not want to convert inferred type variable binders to invisible arguments.To do this properly, we introduce a new
tvbSpecsToBndrVisfunction, which converts a list ofDTyVarBndrSpecs to a list ofDTyVarBndrVises, dropping anyDTyVarBndrSpecs with anInferredSpecin the process. We then usetvbSpecsToBndrVisinpromoteLetDecName, which neatly fixes #585.