todo! macro does not satisfy type-checker when impl Trait is in the return position

[duncpro]

The todo! macro does not satisfy the type-checker when impl Trait is in the return position.

This behavior contradicts the official documentation.

[todo!] can be useful if you are prototyping and just want a placeholder to let your code pass type analysis.

- doc for std::todo macro

Example

// src/main.rs
struct T;

fn make_iter() -> impl Iterator<Item = T> {
    todo!()
}

fn main() {
    make_iter();
}

cargo run

Playground

Expected Behavior

The code to compile normally and panic during execution.

Actual Behavior

The code fails to compile because it does not pass typecheck.

rustc --version --verbose:

rustc 1.82.0 (f6e511eec 2024-10-15)
binary: rustc
commit-hash: f6e511eec7342f59a25f7c0534f1dbea00d01b14
commit-date: 2024-10-15
host: aarch64-apple-darwin
release: 1.82.0
LLVM version: 19.1.1

[theemathas]

Duplicate of #113875

[jieyouxu]

Indeed. Thanks for the report anyway!

[duncpro]

Perhaps a note can be added to the docs for todo! so this doesn't get reported again?