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This patch fixes two rather gnarly test cases: * Trac #16342 (mutual recursion) See Note [Tricky scoping in generaliseTcTyCon] * Trac #16221 (shadowing) See Note [Unification variables need fresh Names] The main changes are: * Substantial reworking of TcTyClsDecls.generaliseTcTyCon This is the big change, and involves the rather tricky function TcHsSyn.zonkRecTyVarBndrs. See Note [Inferring kinds for type declarations] and Note [Tricky scoping in generaliseTcTyCon] for the details. * bindExplicitTKBndrs_Tv and bindImplicitTKBndrs_Tv both now allocate /freshly-named/ unification variables. Indeed, more generally, unification variables are always fresh; see Note [Unification variables need fresh Names] in TcMType * Clarify the role of tcTyConScopedTyVars. See Note [Scoped tyvars in a TcTyCon] in TyCon As usual, this dragged in some more refactoring: * Renamed TcMType.zonkTyCoVarBndr to zonkAndSkolemise * I renamed checkValidTelescope to checkTyConTelescope; it's only used on TyCons, and indeed takes a TyCon as argument. * I folded the slightly-mysterious reportFloatingKvs into checkTyConTelescope. (Previously all its calls immediately followed a call to checkTyConTelescope.) It makes much more sense there. * I inlined some called-once functions to simplify checkValidTyFamEqn. It's less spaghetti-like now. * This patch also fixes Trac #16251. I'm not quite sure why #16251 went wrong in the first place, nor how this patch fixes it, but hey, it's good, and life is short.80dfcee6
