Commit ce987865 authored by Committed by Marge Bot
Revamp the treatment of auxiliary bindings for derived instances
This started as a simple fix for #18321 that organically grew into a much more sweeping refactor of how auxiliary bindings for derived instances are handled. I have rewritten `Note [Auxiliary binders]` in `GHC.Tc.Deriv.Generate` to explain all of the moving parts, but the highlights are: * Previously, the OccName of each auxiliary binding would be given a suffix containing a hash of its package name, module name, and parent data type to avoid name clashes. This was needlessly complicated, so we take the more direct approach of generating `Exact` `RdrName`s for each auxiliary binding with the same `OccName`, but using an underlying `System` `Name` with a fresh `Unique` for each binding. Unlike hashes, allocating new `Unique`s does not require any cleverness and avoid name clashes all the same... * ...speaking of which, in order to convince the renamer that multiple auxiliary bindings with the same `OccName` (but different `Unique`s) are kosher, we now use `rnLocalValBindsLHS` instead of `rnTopBindsLHS` to rename auxiliary bindings. Again, see `Note [Auxiliary binders]` for the full story. * I have removed the `DerivHsBind` constructor for `DerivStuff`—which was only used for `Data.Data`-related auxiliary bindings—and refactored `gen_Data_binds` to use `DerivAuxBind` instead. This brings the treatment of `Data.Data`-related auxiliary bindings in line with every other form of auxiliary binding. Fixes #18321.