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Stuart Cook
870e43eae4
Preserve braces around `self` in use tree pretty printing
The AST pretty printer strips braces from single-item `use` sub-groups, simplifying `use foo::{Bar}` to `use foo::Bar`. However, when the single item is `self`, this produces `use foo::self` which is not valid Rust (E0429) — the grammar requires `use foo::{self}`.
This affects both `stringify!` and `rustc -Zunpretty=expanded`, causing `cargo expand` output to be unparseable when a crate uses `use path::{self}` imports (a common pattern in the ecosystem).
The fix checks whether the single nested item's path starts with `self` before stripping braces. If so, the braces are preserved.
## Example
**before** (`rustc 1.96.0-nightly (3b1b0ef4d 2026-03-11)`):
```rust
#![feature(prelude_import)]
//@ pp-exact
//@ edition:2021
#![allow(unused_imports)]
extern crate std;
#[prelude_import]
use std::prelude::rust_2021::*;
// Braces around `self` must be preserved, because `use foo::self` is not valid Rust.
use std::io::self;
use std::fmt::{self, Debug};
fn main() {}
```
**after** (this branch):
```rust
#![feature(prelude_import)]
//@ pp-exact
//@ edition:2021
#![allow(unused_imports)]
extern crate std;
#[prelude_import]
use std::prelude::rust_2021::*;
// Braces around `self` must be preserved, because `use foo::self` is not valid Rust.
use std::io::{self};
use std::fmt::{self, Debug};
fn main() {}
```
Notice the `use std::io::self` (invalid, E0429) in the before becomes `use std::io::{self}` in the after.