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Fix wrong substitution code #4106

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Merged
merged 1 commit into from
Apr 23, 2020
Merged

Fix wrong substitution code #4106

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2 changes: 1 addition & 1 deletion crates/ra_hir_ty/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -863,7 +863,7 @@ pub trait TypeWalk {
&mut |ty, binders| {
if let &mut Ty::Bound(bound) = ty {
if bound.debruijn >= binders {
*ty = substs.0[bound.index].clone();
*ty = substs.0[bound.index].clone().shift_bound_vars(binders);
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@matklad matklad Apr 23, 2020 •
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Is there perhaps some way we could make similar wrong code crash on all examples, and not only just on the bad ones?

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Like, if this happens to work most of the time, b/c binders is 0, can we remember a number which tells the nesting/how many times we should shift, and than assert everywhere that nesting levels match?

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I don't see how -- if I remember to assert, I can just do it correctly in that place. We could validate types to check that the binders are correct, but that will also only crash if we try to bind to indexes that don't exist.

}
}
},
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41 changes: 41 additions & 0 deletions crates/ra_hir_ty/src/tests/regression.rs
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Expand Up @@ -533,3 +533,44 @@ fn foo(b: Bar) {
"###
);
}

#[test]
fn issue_4053_diesel_where_clauses() {
assert_snapshot!(
infer(r#"
trait BoxedDsl<DB> {
type Output;
fn internal_into_boxed(self) -> Self::Output;
}

struct SelectStatement<From, Select, Distinct, Where, Order, LimitOffset, GroupBy, Locking> {
order: Order,
}

trait QueryFragment<DB: Backend> {}

trait Into<T> { fn into(self) -> T; }

impl<F, S, D, W, O, LOf, DB> BoxedDsl<DB>
for SelectStatement<F, S, D, W, O, LOf, G>
where
O: Into<dyn QueryFragment<DB>>,
{
type Output = XXX;

fn internal_into_boxed(self) -> Self::Output {
self.order.into();
}
}
"#),
@r###"
[66; 70) 'self': Self
[268; 272) 'self': Self
[467; 471) 'self': SelectStatement<F, S, D, W, O, LOf, {unknown}, {unknown}>
[489; 523) '{ ... }': ()
[499; 503) 'self': SelectStatement<F, S, D, W, O, LOf, {unknown}, {unknown}>
[499; 509) 'self.order': O
[499; 516) 'self.o...into()': dyn QueryFragment<DB>
"###
);
}