Stuart Cook 3e1052c6d5 Rollup merge of #153724 - arferreira:fix-lifetime-naming-in-closures, r=jieyouxu ...

Show named lifetime in closure upvar diagnostics

Fixes rust-lang/rust#153545.

When a closure captures a variable whose type involves a named lifetime from the parent function (e.g., `'a`), the borrow checker's region renumbering creates a separate `RegionVid` for each occurrence of the erased lifetime in the closure's upvar type. These new `RegionVid`s have no `external_name`, so diagnostics fall back to synthetic names like `'1`.

This PR recovers the original lifetime name by matching the closure's upvar type against the parent function's parameter type (obtained via `liberate_late_bound_regions`). Both types have the same structure but different region representations, the parent has `ReLateParam`/`ReEarlyParam` with real names, the closure has `ReVar` from renumbering. Walking them in parallel with `for_each_free_region` lets us find which named lifetime corresponds to the anonymous `RegionVid`.

Before:

```rust
error[E0716]: temporary value dropped while borrowed
 --> test.rs:11:21
  |
6 | fn apply<'a>(
  |          -- lifetime `'1` defined here
```

After:

```rust
error[E0716]: temporary value dropped while borrowed
 --> test.rs:11:21
  |
6 | fn apply<'a>(
  |          -- lifetime `'a` defined here
```

The fix gracefully falls back to the existing `'1` naming when it can't match, nested closures, local variables (not parameters), destructuring patterns, or partial captures where the type structures diverge.

2026-03-16 15:01:34 +11:00

..

src

Rollup merge of #153724 - arferreira:fix-lifetime-naming-in-closures, r=jieyouxu

2026-03-16 15:01:34 +11:00

Cargo.toml

Convert to inline diagnostics in rustc_borrowck

2026-02-05 16:55:55 +01:00