Regression on doc-tests with statements and a main function

[Darksonn]

Code

I tried this code:

/// ```
/// # if cfg!(miri) { return; }
/// use playground::my_func;
///
/// fn main() {
///     println!("Hi!");
///     my_func();
/// }
/// ```
pub fn my_func() {
}

On stable, running this doctest succeeds. On beta, it triggers this error:

running 1 test
test src/lib.rs - my_func (line 2) ... FAILED

failures:

---- src/lib.rs - my_func (line 2) stdout ----
error: expected item, found keyword `if`
 --> src/lib.rs:4:1
  |
4 | if cfg!(miri) { return; }
  | ^^ expected item
  |
  = note: for a full list of items that can appear in modules, see <https://doc.rust-lang.org/reference/items.html>

error: aborting due to 1 previous error

Couldn't compile the test.

failures:
    src/lib.rs - my_func (line 2)

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.04s

Version it worked on

It most recently worked on: Latest stable (i.e. rustc 1.86.0)

Version with regression

rustc --version --verbose:

rustc 1.87.0-beta.5 (386abeb93 2025-04-19)
binary: rustc
commit-hash: 386abeb93ab8e683357f54ffe76ae53861b2d984
commit-date: 2025-04-19
host: x86_64-unknown-linux-gnu
release: 1.87.0-beta.5
LLVM version: 20.1.1

@rustbot modify labels: +regression-from-stable-to-beta -regression-untriaged

[apiraino]

Bisecting by running rustdoc --test src/lib.rs (the file contains the reproducible code):

Regression in rust-lang-ci@cdcf730
#138104

cc @GuillaumeGomez @fmease for authoring #138104

bisected with cargo-bisect-rustc v0.6.9

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --without-cargo --preserve --start 2024-02-01 --script test.sh 

[GuillaumeGomez]

Gonna try to take a look as soon as possible.

[cyrgani]

duplicate of #139651?

[GuillaumeGomez]

That's an interesting case: your main function is never run. I'm not sure it's the desired output. However, to keep compatibility, this code should be allowed. So instead, I offer to emit a warning in case there is a main function alongside expressions that only belong to a function.

[GuillaumeGomez]

duplicate of #139651?

Ah yes it is!

[Darksonn]

Yes, we probably need to fix these tests in Tokio regardless. The intent is that the main function should run.

[GuillaumeGomez]

Yep on that we agree. I have a fix ready. Just writing the regression test and then I send it.

[GuillaumeGomez]

Opened #140220.