bca56e82a1
When we are generalizing a super/sub-type, we have to replace type variables with a fresh variable (and not just region variables). So if we know that `Box<?T> <: ?U`, for example, we instantiate `?U` with `Box<?V>` and then relate `Box<?T>` to `Box<?V>` (and hence require that `?T <: ?V`). This change has some complex interactions, however: First, the occurs check must be updated to detect constraints like `?T <: ?U` and `?U <: Box<?T>`. If we're not careful, we'll create a never-ending sequence of new variables. To address this, we add a second unification set into `type_variables` that tracks type variables related through **either** equality **or** subtyping, and use that during the occurs-check. Second, the "fudge regions if ok" code was expecting no new type variables to be created. It must be updated to create new type variables outside of the probe. This is relatively straight-forward under the new scheme, since type variables are now independent from one another, and any relations are moderated by pending subtype obliations and so forth. This part would be tricky to backport though. cc #18653 cc #40951
20 lines
652 B
Rust
20 lines
652 B
Rust
// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// Regression test for #40951.
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const FOO: [&'static str; 1] = ["foo"];
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fn find<T: PartialEq>(t: &[T], element: &T) { }
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fn main() {
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let x = format!("hi");
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find(&FOO, &&*x);
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}
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