rustdoc cuts off the last line in a `#[doc]` attribute if it only has a single character

[nicholasbishop]

When using #[doc = include_str!("...")] to insert another file as a docstring, it seems that the last line gets cut off if it contains only one character.

src/inc1:

inc1
ab

src/inc2:

inc2
x

(Both inc files have a trailing new line.)

src/lib.rs:

#[doc = include_str!("inc1")]  // OK: "inc1 ab"
pub const A: usize = 1;

#[doc = include_str!("inc2")]  // Bad: "inc2"
pub const B: usize = 2;

Running cargo doc --open on the above produces output like this:

A inc1 ab 
B inc2

That is, the inc1 file gets included correctly, but the inc2 file loses its second line. This bug only seems to happen if the last line is a single character.

Meta

Reproduced this bug on both stable and nightly.

rustc --version --verbose:

rustc 1.56.1 (59eed8a2a 2021-11-01)
binary: rustc
commit-hash: 59eed8a2aac0230a8b53e89d4e99d55912ba6b35
commit-date: 2021-11-01
host: x86_64-unknown-linux-gnu
release: 1.56.1
LLVM version: 13.0.0

rustc +nightly --version --verbose:

rustc 1.58.0-nightly (4961b107f 2021-11-04)
binary: rustc
commit-hash: 4961b107f204e15b26961eab0685df6be3ab03c6
commit-date: 2021-11-04
host: x86_64-unknown-linux-gnu
release: 1.58.0-nightly
LLVM version: 13.0.0

[jyn514]

@nicholasbishop does this also happen for string constants and other things using include_str!? Or just the doc attribute?

[nicholasbishop]

Oh I didn't think to check that. Looks like the bug doesn't reproduce with a non-doc use of include_str.

This runs without error:

fn main() {
    let inc1 = include_str!("inc1");
    let inc2 = include_str!("inc2");

    assert_eq!(inc1, "inc1\nab\n");
    assert_eq!(inc2, "inc2\nx\n");
}

[jyn514]

Ok cool and follow-up question - does #[doc = "inc2\nx\n"] have the same issue? Or only with include_str?

[nicholasbishop]

That does reproduce the issue.

#[doc = "inc2\nx\n"]
pub const C: usize = 2;

The rustdoc output looks like C inc2.

[jyn514]

cc @GuillaumeGomez, this is probably related to your changes to try and make the indentation smarter.

[GuillaumeGomez]

You mean removing the smart indent? ;)

But yes, very likely. I'll take a look.