Fix crash in Data.Data instance for HsCtxt

sheafrequested to merge
wip/hsctxt-data-instance into master

A quick fix for a crash I ran into today with -ddump-tc-ast (#27359 (closed)).

The Data.Data instance for HsCtxt contained an error for the toConstr method, which could trigger for example when looking at -ddump-tc-ast traces. This MR replaces it with the abstractConstr pattern used in the rest of the codebase.

Edited by sheaf

Merge request reports