lazy_type_alias causes lifetime error #114221
Description
I tried this code:
tests/ui/regions/regions-scope-chain-example.rs
// run-pass #![allow(dead_code)] #![allow(unused_variables)] // This is an example where the older inference algorithm failed. The // specifics of why it failed are somewhat, but not entirely, tailed // to the algorithm. Ultimately the problem is that when computing the // mutual supertype of both sides of the `if` it would be faced with a // choice of tightening bounds or unifying variables and it took the // wrong path. The new algorithm avoids this problem and hence this // example typechecks correctly. // pretty-expanded FIXME #23616 enum ScopeChain<'a> { Link(Scope<'a>), End } type Scope<'a> = &'a ScopeChain<'a>; struct OuterContext; struct Context<'a> { foo: &'a OuterContext } impl<'a> Context<'a> { fn foo(&mut self, scope: Scope) { let link = if 1 < 2 { let l = ScopeChain::Link(scope); self.take_scope(&l); l } else { ScopeChain::Link(scope) }; self.take_scope(&link); } fn take_scope(&mut self, x: Scope) { } } fn main() { }without `-Zcrate-attr=feature(lazy_type_alias)´: no warnings
with -Zcrate-attr=feature(lazy_type_alias):
error[E0597]: `l` does not live long enough --> tests/ui/regions/regions-scope-chain-example.rs:31:29 | 28 | fn foo(&mut self, scope: Scope) { | ----- has type `Scope<'1>` 29 | let link = if 1 < 2 { 30 | let l = ScopeChain::Link(scope); | - binding `l` declared here 31 | self.take_scope(&l); | ----------------^^- | | | | | borrowed value does not live long enough | argument requires that `l` is borrowed for `'1` 32 | l 33 | } else { | - `l` dropped here while still borrowed error[E0505]: cannot move out of `l` because it is borrowed --> tests/ui/regions/regions-scope-chain-example.rs:32:13 | 28 | fn foo(&mut self, scope: Scope) { | ----- has type `Scope<'1>` 29 | let link = if 1 < 2 { 30 | let l = ScopeChain::Link(scope); | - binding `l` declared here 31 | self.take_scope(&l); | ------------------- | | | | | borrow of `l` occurs here | argument requires that `l` is borrowed for `'1` 32 | l | ^ move out of `l` occurs here error[E0597]: `link` does not live long enough --> tests/ui/regions/regions-scope-chain-example.rs:36:25 | 28 | fn foo(&mut self, scope: Scope) { | ----- has type `Scope<'1>` 29 | let link = if 1 < 2 { | ---- binding `link` declared here ... 36 | self.take_scope(&link); | ----------------^^^^^- | | | | | borrowed value does not live long enough | argument requires that `link` is borrowed for `'1` 37 | } | - `link` dropped here while still borrowed error: aborting due to 3 previous errors rustc 1.73.0-nightly (04abc370b 2023-07-28) binary: rustc commit-hash: 04abc370b9f3855b28172b65a7f7d5a433f41412 commit-date: 2023-07-28 host: x86_64-unknown-linux-gnu release: 1.73.0-nightly LLVM version: 16.0.5 Metadata
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Area: Variance (https://doc.rust-lang.org/nomicon/subtyping.html)Category: This is a bug.`#![feature(lazy_type_alias)]`Status: A Minimal Complete and Verifiable Example has been found for this issueRelevant to the compiler team, which will review and decide on the PR/issue.This issue requires a nightly compiler in some way.
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