[WIP] Move placeholder error handling to before region inference #142623
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Wow, a merge conflict with upstream for a commit I JUST PUSHED, that's record time! |
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Revise the extra `r: 'static` constraints added upon universe issues to add an explanation, and use that explanation during constraint blame search. This greatly simplifies the region inference logic, which now does not need to reverse-engineer the event that caused a region to outlive 'static.
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This PR breaks out yet another part of #130227. It prepares for the removal of precise placeholder tracking by colocating detecting placeholder errors for higher-ranked relations (placeholders outliving existentials that can't name them, other placeholders) with the preprocessing step that adds outlives-static constraints.
For stepping-on-toes reasons it is currently based on #140737, but
can be rebased on regular master and merged separatelynope that's a terrible idea actually, it relies on some of the tracking introduced there.This step also makes region errors more fine-grained, which is useful to simplify the error reporting pipeline, which is currently based on a very brittle method of reconstructing an error event after the fact to figure out what went wrong. Doing that is left as future work, though.
This changes the logic of error reporting slightly to not emit errors for placeholder/higher kinded constraints if there are other borrowck errors. This somewhat lessens the flood of errors and was described as if anything an improvement by @nikomatsakis in informal review.
r? lcnr
WIP waiting for #140737 to land.