Instrumenting async_trait methods drops location of compilation errors

[kleimkuhler]

Bug Report

Version

• tracing v0.1.15
• tracing-futures v0.2.4

Platform

Linux

Crates

• async-trait v0.1.36

Description

Instrumenting an async_trait method drops the location of compilation errors.

use async_trait::async_trait;

#[derive(Debug)]
struct A {
    x: usize,
}

#[async_trait]
trait Set {
    async fn set(&mut self);
}

#[async_trait]
impl Set for A {
    #[tracing::instrument]
    async fn set(&mut self) {
        self.x = "error";
    }
}

fn main() {
    println!("Hello, world!");
}

I expected to see the following error from the above:

error[E0308]: mismatched types
  --> src/main.rs:17:18
   |
17 |         self.x = "error";
   |                  ^^^^^^^ expected `usize`, found `&str`

error: aborting due to previous error

Instead, this is the error:

error[E0308]: mismatched types
  --> src/main.rs:15:5
   |
15 |     #[tracing::instrument]
   |     ^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&str`

error: aborting due to previous error

Extra details

I originally came across this error in a less minimal reproduction, but the
error had even less location details as the above.

error[E0277]: the trait bound `(): core::future::future::Future` is not satisfied
  |
  = note: required by `core::future::future::Future::poll`
error: aborting due to previous error

Note that there is no file or code location mentioned!

It was unable to point at the actual #[tracing::instrument] attribute, and on
top of that the error ended up being in a subdirectory of the crate.

I haven't been able to reproduce that in this example.

[hawkw]

This is pretty weird. I'm CCing @nightmared, who wrote the original instrument/async_trait integration --- it looks like a compiler diagnostic span (not to be confused with a tracing::Span!) is getting misplaced someplace in there.

[hawkw]

At a glance, I think that maybe this quote!, here:

tracing/tracing-attributes/src/lib.rs

Lines 231 to 237 in 7bc225a

	quote!(
	#(#attrs) *
	#sig {
	#(#stmts) *
	}
	)
	.into()

needs to be a quote_spanned! to propagate the span of the input function, but I'm not sure --- haven't tested it or anything.

[nightmared]

I fear this may be the same underlying issue as #755.

nightmared@placebo:tracing-async-trait-bug-repro$ cargo build
    Updating crates.io index
  Downloaded async-trait v0.1.36
  Downloaded 1 crate (24.4 KB) in 0.67s
   Compiling tracing-core v0.1.10
   Compiling tracing-attributes v0.1.8
   Compiling async-trait v0.1.36
   Compiling tracing v0.1.15
   Compiling tracing-futures v0.2.4
   Compiling bug-repro v0.1.0 (/home/nightmared/dev/tmp/tracing-async-trait-bug-repro)
error[E0308]: mismatched types
  --> src/lib.rs:17:18
   |
17 |         self.x = "error";
   |                  ^^^^^^^ expected `usize`, found `&str`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
error: could not compile `bug-repro`.

To learn more, run the command again with --verbose.
nightmared@placebo:tracing-async-trait-bug-repro$ cargo +stable  build
   Compiling proc-macro2 v1.0.6
   Compiling unicode-xid v0.2.0
   Compiling syn v1.0.5
   Compiling lazy_static v1.4.0
   Compiling cfg-if v0.1.10
   Compiling tracing-core v0.1.10
   Compiling quote v1.0.2
   Compiling pin-project-internal v0.4.13
   Compiling tracing-attributes v0.1.8
   Compiling async-trait v0.1.36
   Compiling tracing v0.1.15
   Compiling pin-project v0.4.13
   Compiling tracing-futures v0.2.4
   Compiling bug-repro v0.1.0 (/home/nightmared/dev/tmp/tracing-async-trait-bug-repro)
error[E0308]: mismatched types
  --> src/lib.rs:15:5
   |
15 |     #[tracing::instrument]
   |     ^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&str`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
error: could not compile `bug-repro`.

To learn more, run the command again with --verbose.

TL;DR: works in nightly, but not on stable.

[hawkw]

Hmm, that's interesting --- @kleimkuhler, do you have a minute to try with a nightly compiler?

[kleimkuhler]

Yep it looks like this is not an error on nightly. The example I provided:

error[E0308]: mismatched types
  --> src/main.rs:17:18
   |
17 |         self.x = "error";
   |                  ^^^^^^^ expected `usize`, found `&str`

error: aborting due to previous error

In the original situation I came across this error, it also provides the file and line number.

[hawkw]

In that case, this seems like a compiler bug --- we can check rust-lang/rust for issues related to spans in nested proc-macros?

[taiki-e]

This is due to rust-lang/rust#43081, and should be fixed by rust-lang/rust#72287, rust-lang/rust#72393, rust-lang/rust#72388, or rust-lang/rust#72306 (see rust-lang/rust#43081 (comment))

[hawkw]

Thanks @taiki-e!

[hawkw]

Closing this, since it's an upstream issue and the fix should make it to stable eventually.