Use call_site hygiene to avoid unused qualification

[mu001999]

Motivation

Previous attempt: #7777
More context: rust-lang/rust#149873

Direct using user's span here will lead to unexpected warning of unused qualification for user code.

Solution

As @taiki-e suggests (rust-lang/rust#149873 (comment)), use Span::call_site hygiene here to help the lint can use Span::from_expansion to check it.

Have tested this solution in https://github.com/mu001999-contrib/tokio-unexpected-warning, the output is:

~/r/unexpected-warning @ main » cd base 
~/r/u/base @ main » cargo check --tests
    Checking base v0.1.0 (/Users/mu00/repos/unexpected-warning/base)
error: unnecessary qualification
 --> base/src/lib.rs:5:5
  |
5 |     if true {}
  |     ^^
  |
  = note: requested on the command line with `-D unused-qualifications`

error: could not compile `base` (lib test) due to 1 previous error
~/r/u/base @ main [101] » cd ../new          
~/r/u/new @ main » cargo check --tests
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.01s

The difference is that the new crate uses the dependency tokio = { git = "https://github.com/mu001999-contrib/tokio", branch = "fix/use-callsite-span", features = ["full"] }

[Darksonn]

It sounds like the output is still incorrect. Am I mistaken? What is the output prior to this change?

[mu001999]

It sounds like the output is still incorrect. Am I mistaken? What is the output prior to this change?

The above output have two parts, base is the output prior to this change:

~/r/unexpected-warning @ main » cd base 
~/r/u/base @ main » cargo check --tests
    Checking base v0.1.0 (/Users/mu00/repos/unexpected-warning/base)
error: unnecessary qualification
 --> base/src/lib.rs:5:5
  |
5 |     if true {}
  |     ^^
  |
  = note: requested on the command line with `-D unused-qualifications`

error: could not compile `base` (lib test) due to 1 previous error

The new is the output after this change:

~/r/u/base @ main [101] » cd ../new          
~/r/u/new @ main » cargo check --tests
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.01s

[Darksonn]

Ah, so the error went away. That's great. Could we test this under tests-build?

[mu001999]

Could we test this under tests-build?

Yes, I have added one.

[Darksonn]

It looks ok to me, but I'd like to hear from @taiki-e too.

[djc]

Awesome, thanks!