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由 Niko Matsakis 提交于
This patch makes error handling for region inference failures more uniform by not reporting *any* region errors until the reigon inference step. This requires threading through more information about what caused a region constraint, so that we can still give informative error messages. I have only taken partial advantage of this information: when region inference fails, we still report the same error we always did, despite the fact that we now know precisely what caused the various constriants and what the region variable represents, which we did not know before. This change is required not only to improve error messages but because the region hierarchy is not in fact fully known until regionck, because it is not clear where closure bodies fit in (our current treatment is unsound). Moreover, the relationships between free variables cannot be fully determined until type inference is otherwise complete. cc #3238.
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