Commit 1e2e82aa authored by 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.
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