rollup merge of #24162: pnkfelix/fsk-detect-duplicate-loop-labels

Check for duplicate loop labels in function bodies.

See also: http://internals.rust-lang.org/t/psa-rejecting-duplicate-loop-labels/1833

The change, which we are putting in as future-proofing in preparation for future potential additions to the language (namely labeling arbitrary blocks and using those labels in borrow expressions), means that code like this will start emitting warnings:

```rust
fn main() {
    { 'a: loop { break; } }
    { 'a: loop { break; } }
}
```

To make the above code compile without warnings, write this instead:

```rust
fn main() {
    { 'a: loop { break; } }
    { 'b: loop { break; } }
}
```

Since this change is only introducing a new warnings, this change is non-breaking.

Fix #21633

0 files changed, 0 insertions, 0 deletions