Commit c90eca55 authored by Committed by Marge Bot
PmCheck: Record type constraints arising from existentials in `PmCoreCt`s
In #17703 (a follow-up of !2192), we established that contrary to my belief, type constraints arising from existentials in code like ```hs data Ex where Ex :: a -> Ex f _ | let x = Ex @Int 15 = case x of Ex -> ... ``` are in fact useful. This commit makes a number of refactorings and improvements to comments, but fundamentally changes `addCoreCt.core_expr` to record the type constraint `a ~ Int` in addition to `x ~ Ex @a y` and `y ~ 15`. Fixes #17703.
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