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Simon Peyton Jones authored
The trouble here is that given {-# LANGUAGE DataKinds, TypeFamilies #-} data instance Foo a = Bar (Bar a) we want to get a sensible message that we can't use the promoted 'Bar' constructor until after its definition; it's a staging error. Bud the staging mechanism that we use for vanilla data declarations don't work here. Solution is to perform strongly-connected component analysis on the instance declarations. But that in turn means that we need to track free-variable information on more HsSyn declarations, which is why so many files are touched. All the changes are boiler-platey except the ones in TcInstDcls.
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