Commit 1e2e82aa authored by Simon Peyton Jones's avatar Simon Peyton Jones Committed by Marge Bot

Fix a bad error in tcMatchTy

This patch fixes #17395, a very subtle and hard-to-trigger
bug in tcMatchTy.  It's all explained in
  Note [Matching in the presence of casts (2)]

I have not added a regression test because it is very hard
to trigger it, until we have the upcoming mkAppTyM patch,
after which lacking this patch means you can't even compile
the libraries.
parent d2471964
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