mirror of https://github.com/rust-lang/rust
43 lines
1.3 KiB
Rust
43 lines
1.3 KiB
Rust
//@ check-pass
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#![feature(offset_of_nested)]
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#![deny(dead_code)]
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// This struct contains a projection that can only be normalized after getting the field type.
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struct A<T: Project> {
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a: <T as Project>::EquateParamTo,
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}
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// This is the inner struct that we want to get.
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struct MyFieldIsNotDead {
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not_dead: u8,
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}
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// These are some helpers.
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// Inside the param env of `test`, we want to make it so that it considers T=MyFieldIsNotDead.
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struct GenericIsEqual<T>(T);
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trait Project {
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type EquateParamTo;
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}
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impl<T> Project for GenericIsEqual<T> {
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type EquateParamTo = T;
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}
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fn test<T>() -> usize
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where
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GenericIsEqual<T>: Project<EquateParamTo = MyFieldIsNotDead>,
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{
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// The first field of the A that we construct here is
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// `<GenericIsEqual<T>> as Project>::EquateParamTo`.
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// Typeck normalizes this and figures that the not_dead field is totally fine and accessible.
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// But importantly, the normalization ends up with T, which, as we've declared in our param
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// env is MyFieldDead. When we're in the param env of the `a` field, the where bound above
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// is not in scope, so we don't know what T is - it's generic.
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// If we use the wrong param env, the lint will ICE.
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std::mem::offset_of!(A<GenericIsEqual<T>>, a.not_dead)
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}
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fn main() {
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test::<MyFieldIsNotDead>();
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}
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