Require coherence of supertrait associated item bounds for dyn-compability#158915
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Require coherence of supertrait associated item bounds for dyn-compability#158915theemathas wants to merge 2 commits into
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…ics. See rust-lang#154662 These tests will be fixed in a subsequent commit.
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I'm unsure of what to do with the now-failing tests. I'm also rather unsure of my code in general. Please be careful with the review to make sure I didn't do anything stupid. Thank you. |
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…ility Fixes rust-lang#154662 In a `dyn` type, if multiple bounds are specified via supertraits for the same associated item, then we previously accepted them if the relevant trait's generics are different, even if the bounds conflict. This was unsound, since those generics could end up being instantiated with identical concrete types, causing the `dyn` type to have two different "values" for the same bound. Thus, if a trait has multiple supertrait bounds for the same associated item, we check whether those bounds are coherent, similarly to how we check for overlap between impulse (i.e., we check if the generics could be instantiated to be the same while the "values" of the bounds are different). If the bounds are incoherent, then we consider the trait to be dyn-incompatible.
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This PR is an alternative to #157710. However, unlike that PR, this PR does not address #150936.
Fixes #154662
In a
dyntype, if multiple bounds are specified via supertraits for the same associated item, then we previously accepted them if the relevant trait's generics are different, even if the bounds conflict.This was unsound, since those generics could end up being instantiated with identical concrete types, causing the
dyntype to have two different "values" for the same bound.Thus, if a trait has multiple supertrait bounds for the same associated item, we check whether those bounds are coherent, similarly to how we check for overlap between impulse (i.e., we check if the generics could be instantiated to be the same while the "values" of the bounds are different). If the bounds are incoherent, then we consider the trait to be dyn-incompatible.
r? @fmease