commit ade745e214f95c88940a28944b6e381229aca535
author Matthias Krüger <476013+matthiaskrgr@users.noreply.github.com> Sat Jun 14 11:27:09 2025 +0200
committer GitHub <noreply@github.com> Sat Jun 14 11:27:09 2025 +0200
tree 5085061483dd5c847bcac7e097f4510fce98c7ed
parent 64033a4ee541c3e9c178fd593e979c74bb798cdc
parent 855ea48ccc01b040539d1d32d76cd4cd472aa7c0

Rollup merge of #140593 - m-ou-se:some-temp, r=Nadrieril

Temporary lifetime extension through tuple struct and tuple variant constructors

This makes temporary lifetime extension work for tuple struct and tuple variant constructors, such as `Some()`.

Before:
```rust
let a = &temp(); // Extended
let a = Some(&temp()); // Not extended :(
let a = Some { 0: &temp() }; // Extended
```

After:
```rust
let a = &temp(); // Extended
let a = Some(&temp()); // Extended
let a = Some { 0: &temp() }; // Extended
```

So, with this change, this works:

```rust
let a = Some(&String::from("hello")); // New: String lifetime now extended!

println!("{a:?}");
```

Until now, we did not extend through tuple struct/variant constructors (like `Some`), because they are function calls syntactically, and we do not want to extend the String lifetime in:

```rust
let a = some_function(&String::from("hello")); // String not extended!
```

However, it turns out to be very easy to distinguish between regular functions and constructors at the point where we do lifetime extension.

In practice, constructors nearly always use UpperCamelCase while regular functions use lower_snake_case, so it should still be easy to for a human programmer at the call site to see whether something qualifies for lifetime extension or not.

This needs a lang fcp.

---

More examples of what will work after this change:

```rust
let x = Person {
    name: "Ferris",
    job: Some(&Job { // `Job` now extended!
        title: "Chief Rustacean",
        organisation: "Acme Ltd.",
    }),
};

dbg!(x);
```

```rust
let file = if use_stdout {
    None
} else {
    Some(&File::create("asdf")?) // `File` now extended!
};

set_logger(file);
```

```rust
use std::path::Component;

let c = Component::Normal(&OsString::from(format!("test-{num}"))); // OsString now extended!

assert_eq!(path.components.first().unwrap(), c);
```