Commit bfdccac6 authored by Committed by Marge Bot
Fix desugaring of record updates on data families
This fixes a long-standing bug in the desugaring of record updates for data families, when the latter involves a GADT. It's all explained in Note [Update for GADTs] in GHC.HsToCore.Expr. Building the correct cast is surprisingly tricky, as that Note explains. Fixes #18809. The test case (in indexed-types/should_compile/T18809) contains several examples that exercise the dark corners.
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