Make dyn Trait implement its super traits as well
#415
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chalk-solve/src/clauses.rs
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| builder.push_binders(&qwc, |builder, wc| match &wc { | ||
| // For the implemented traits, we need to elaborate super traits and add where clauses from the trait | ||
| WhereClause::Implemented(trait_ref) => { | ||
| let mut seen_traits = FxHashSet::default(); |
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Hmm, this is .. ungreat. I think that ideally we'd have a query like "supertraits of this trait def-id" that the db offers, so that this calculation can be cached. Certainly rustc has such a query. I'm not sure exactly how to manage this -- I guess the pattern is to have the RustIrDatabase trait have hooks for places we would like to have queries, and to have "default callbacks" that you can use to actually implement the query?
(This preserves independence from salsa -- if we didn't care about that, we could use salsa's existing facilities here I think for composable salsa databases.)
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Hmm this query would have to return something like Binders<Vec<Binders<TraitRef>>> (outer binders for the original trait's parameters, inner binders for for<'a> super trait bounds), right?
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Yes... in rustc, we skip the outer binders, but you're correct that ideally it'd have a Binders type. Perhaps -- just for the purposes of this PR -- you could move this logic to a method on TraitDatum?
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Well, this turned out to be more interesting than expected, because if we have Foo: for<'a> Bar<'a> and Bar<'a>: for<'b> Baz<'a, 'b> we need to collapse the binders.
I've extracted it to a function for now; I'm not sure whether it makes sense to be on TraitDatum, but if you want I can move it there.
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So I've decided that this is going down the right direction after all. Before landing, though, we should probably convert #203 into a kind of "checklist of rules" to add, so we can track what's done and not done. Also, I think we should probably be extending the chalk book with documenting on these rules we're adding here, though that could be separate items on the check-list. |
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This implements the impl rules from rust-lang#203, as far as I understood them. It doesn't do the well-formedness or object safety rules.
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Rebased and added doc comments. |
This implements the impl rules from #203, as far as I understood them. It doesn't do the well-formedness or object safety rules.