Make TAITs and ATPITs capture late-bound lifetimes in scope by compiler-errors · Pull Request #122103 · rust-lang/rust (original) (raw)
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This generalizes the behavior that RPITs have, where they duplicate their in-scope lifetimes so that they will always reify late-bound lifetimes that they capture. This allows TAITs and ATPITs to properly error when they capture in-scope late-bound lifetimes.
Fixes #122093 and therefore #120700 (comment)
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| @@ -1,8 +1,14 @@ |
|---|
| error: cannot capture late-bound lifetime in type alias impl trait |
| --> $DIR/escaping-bound-var.rs:9:57 |
| error: higher kinded lifetime bounds on nested opaque types are not supported yet |
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This error message sucks but is improved by #122100. Separated that from this PR for reviewability.
Alternatively, we could implement this restriction in a far simpler manner by just checking if any late-bound vars are in scope of an opaque via a HIR walker. But given that we may want to support this eventually, and the rest of the compiler is already set up to support this because of RPIT, I'd rather do this the right way.
yea, I prefer mirroring RPITs, even if that means we duplicate all the lifetimes from parents only to then immediately always ignore the parent lifetimes
@bors r+
📌 Commit 0241618 has been approved by oli-obk
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📌 Commit e88c048 has been approved by oli-obk
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📌 Commit 74d5bbb has been approved by oli-obk
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bors added a commit to rust-lang-ci/rust that referenced this pull request
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request
Rollup merge of rust-lang#122103 - compiler-errors:taits-capture-everything, r=oli-obk
Make TAITs and ATPITs capture late-bound lifetimes in scope
This generalizes the behavior that RPITs have, where they duplicate their in-scope lifetimes so that they will always reify late-bound lifetimes that they capture. This allows TAITs and ATPITs to properly error when they capture in-scope late-bound lifetimes.
r? @oli-obk cc @aliemjay
Fixes rust-lang#122093 and therefore rust-lang#120700 (comment)
| // Only check the parent generics, which will ignore any of the |
| // duplicated lifetime args that come from reifying late-bounds. |
| for (i, arg) in opaque_type_key.args.iter().take(parent_generics.count()).enumerate() { |
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The parent generics are bivariant and can easily be unconstrained lifetime variables. This caused #122307.
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Status: Waiting on bors to run and complete tests. Bors will change the label on completion.
Relevant to the compiler team, which will review and decide on the PR/issue.