Rustdoc: Test fails on "unresolved import" though test doesn't use any crate

[mirao]

I tried this code (src/main.rs):

use regex::Regex;

/// ```
/// assert!(true)
/// ```
fn main() {
    println!("Hello, world!");
    let regex = Regex::new("^Hello").unwrap();
    println!("{}", regex);
}

with Cargo.toml

[package]
name = "hello_world"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
regex = "1.6.0"

I run rustdoc --test src/main.rs

I expected to see this happen:

running 1 test
test src/main.rs - main (line 1) ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.20s

Instead, this happened:

error[E0432]: unresolved import `regex`
 --> src/main.rs:1:5
  |
1 | use regex::Regex;
  |     ^^^^^ maybe a missing crate `regex`?
  |
  = help: consider adding `extern crate regex` to use the `regex` crate

error: aborting due to previous error

For more information about this error, try `rustc --explain E0432`.

Note that cargo run works well

$ cargo run
   Compiling hello_world v0.1.0 (/home/mirao/workspace/rust/hello_world)
    Finished dev [unoptimized + debuginfo] target(s) in 1.34s
     Running `target/debug/hello_world`
Hello, world!
^Hello

Meta

rustc --version --verbose:

rustc 1.64.0 (a55dd71d5 2022-09-19)
binary: rustc
commit-hash: a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52
commit-date: 2022-09-19
host: x86_64-unknown-linux-gnu
release: 1.64.0
LLVM version: 14.0.6

rustdoc --version

rustdoc 1.64.0 (a55dd71d5 2022-09-19)

I'm running Ubuntu 22.04

[mirao]

If I use qualified name for Regex in main() without using import, then test passes:

/// ```
/// assert!(true)
/// ```
fn main() {
    println!("Hello, world!");
    let regex = regex::Regex::new("^Hello").unwrap();
    println!("{}", regex);
}

$ rustdoc --test src/main.rs

running 1 test
test src/main.rs - main (line 1) ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.21s

[fmease]

You are invoking rustdoc on src/main.rs which knows nothing about Cargo's package manifest Cargo.toml. You should instead be using cargo test or cargo test --bins to run tests.

The rustdoc binary is the low-level documentation generator invoked by the high-level cargo test & cargo doc commands (which can resolve your dependencies like regex in this case) similar to the low-level rustc binary which is invoked by cargo build. You will almost never need to invoke rustc / rustdoc directly.

@rustbot label invalid

[rustbot]

Error: Label invalid can only be set by Rust team members

Please file an issue on GitHub at triagebot if there's a problem with this bot, or reach out on #t-infra on Zulip.

[fmease]

Regarding your comment:

If I use qualified name for Regex in main() without using import, then test passes:

This is due to an unrelated reason (what I said about rustdoc --test vs. cargo test still applies): rustdoc doesn't perform full semantic analysis as far as I know and assumes a thing or two about the validity of your program.
E.g. the following file also gets successfully documented:

fn main() {
    i_do_not_exist;
}

[fmease]

Thanks for your report! However, none of this is a bug. The issues you are seeing a due to the incorrect use of the provided Rust tools. The issue with rustdoc accepting several semantically malformed programs is well-known and a won't-fix.

[mirao]

You should instead be using cargo test or cargo test --bins to run tests.

But it doesn't run docs tests in my case: #50784
Nevertheless I understand that rustdoc is a low level tool and ideally cargo test should be used. It makes sense.

[fmease]

Ah, I see. That's bothersome :(

So essentially, this issue then becomes a duplicate of #50784, right?

[mirao]

Duplicate of #50784