Rewrite assumptions on binders goal - #742
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lcnr
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Jul 31, 2026
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| - Marker traits | ||
| - Proving auto traits for futures/coroutines (without lots of spurrious errors) | ||
| - Supporting implied bounds on uses of GATs (`where for<'a> T::Assoc<'a>: Trait`) | ||
| - Better handling of region constraints originating inside closures involving parent body regions | ||
| - Soundly supporting subtyping of higher ranked types and other functionality involving binders (`for<'a>`) |
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mind linking to rust-lang tracking issues/bugs here?
lcnr
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Jul 31, 2026
Co-authored-by: lcnr <rust@lcnr.de>
lcnr
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Jul 31, 2026
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| ### Interactions with -Zhigher-ranked-assumptions | ||
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| The `-Zhigher-ranked-assumptions` flag currently exists and tries so solve some of the problems caused by this, but it is not fully general and likely not the implementation strategy we want when solving all problems in this area. |
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| The `-Zhigher-ranked-assumptions` flag currently exists and tries so solve some of the problems caused by this, but it is not fully general and likely not the implementation strategy we want when solving all problems in this area. | |
| The `-Zhigher-ranked-assumptions` flag currently exists and tries so solve some of the problems caused by this, it does so in a very targeted way and cannot be easily generalized to support all our use-cases. |
lcnr
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Jul 31, 2026
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| Ideally we would implement a version of `-Zhigher-ranked-assumptions` which works for *all* binders, not just witness types of futures. And ideally it would be cleverer and handle the transitiveness of outlives assumptions, much like we do for normal region outlives where clauses. | ||
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| This goal will likely subsume the `-Zhigher-ranked-assumptions` flag, though we do intend to pursue a minimal stabilization of something quite similar to it. |
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| Ideally we would implement a version of `-Zhigher-ranked-assumptions` which works for *all* binders, not just witness types of futures. And ideally it would be cleverer and handle the transitiveness of outlives assumptions, much like we do for normal region outlives where clauses. | |
| This goal will likely subsume the `-Zhigher-ranked-assumptions` flag, though we do intend to pursue a minimal stabilization of something quite similar to it. | |
| This work subsumes `-Zhigher-ranked-assumptions` with an implementation which will for *all* binders, not just coroutine witness types. It handles the transitiveness of outlives assumptions, much like we do for normal region outlives where clauses and will handles arbitrary `TypeOutlives` constraints. |
lcnr
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Jul 31, 2026
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| ### Interactions with Polonius | ||
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| This goal is only intending to change how we handle regions *before* borrow checking and should in theory not interact with borrow checking other than resulting in potentially different region constraints for the borrow checker to check. |
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| This goal is only intending to change how we handle regions *before* borrow checking and should in theory not interact with borrow checking other than resulting in potentially different region constraints for the borrow checker to check. | |
| This goal only changes how we handle region constraints before passing them to borrow checking and should in theory not interact with borrow checking other than changing the set of relevant region constraints. It is entirely distinct from polonius. |
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nxsaken
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☔ The latest upstream changes (possibly #756) made this pull request unmergeable. Please resolve the merge conflicts. |
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I also want to rename the zulip stream I think so this shouldn't be merged before I do that and update the links :>
cc @rust-lang/types
the assumptions on binders goal got to a point where we now have a pretty good sense of things which means we can reframe the goal in terms of all the work that we actually want to go and do, rather than just being a kind of nebulous "we're going to explore and figure stuff out"
the team ask is now large instead of medium because there'll be things we want to stabilize here which means we'll probably want to talk about things in types meetings and whatnot.
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