Tiny difference of the diagnostics for generator on some environment

[JohnTitor]

Follow-up of #71182
Consider this example: #67893 (comment)

It emits the stderr on my local (x86_64-unknown-linux-gnu):

error[E0277]: `std::sync::MutexGuard<'_, ()>` cannot be sent between threads safely
  --> $DIR/issue-67893.rs:9:5
   |
LL | fn g(_: impl Send) {}
   |              ---- required by this bound in `g`
...
LL |     g(issue_67893::run())
   |     ^ `std::sync::MutexGuard<'_, ()>` cannot be sent between threads safely
   | 
  ::: $DIR/auxiliary/issue_67893.rs:7:20
   |
LL | pub async fn run() {
   |                    - within this `impl std::future::Future`
   |
   = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `std::sync::MutexGuard<'_, ()>`
   = note: required because it appears within the type `for<'r, 's, 't0, 't1, 't2, 't3> {std::future::ResumeTy, std::sync::Arc<std::sync::Mutex<()>>, &'r std::sync::Mutex<()>, std::result::Result<std::sync::MutexGuard<'s, ()>, std::sync::PoisonError<std::sync::MutexGuard<'t0, ()>>>, &'t1 std::sync::MutexGuard<'t2, ()>, std::sync::MutexGuard<'t3, ()>, (), impl std::future::Future}`
   = note: required because it appears within the type `[static generator@DefId(15:11 ~ issue_67893[8787]::run[0]::{{closure}}[0]) for<'r, 's, 't0, 't1, 't2, 't3> {std::future::ResumeTy, std::sync::Arc<std::sync::Mutex<()>>, &'r std::sync::Mutex<()>, std::result::Result<std::sync::MutexGuard<'s, ()>, std::sync::PoisonError<std::sync::MutexGuard<'t0, ()>>>, &'t1 std::sync::MutexGuard<'t2, ()>, std::sync::MutexGuard<'t3, ()>, (), impl std::future::Future}]`
   = note: required because it appears within the type `std::future::from_generator::GenFuture<[static generator@DefId(15:11 ~ issue_67893[8787]::run[0]::{{closure}}[0]) for<'r, 's, 't0, 't1, 't2, 't3> {std::future::ResumeTy, std::sync::Arc<std::sync::Mutex<()>>, &'r std::sync::Mutex<()>, std::result::Result<std::sync::MutexGuard<'s, ()>, std::sync::PoisonError<std::sync::MutexGuard<'t0, ()>>>, &'t1 std::sync::MutexGuard<'t2, ()>, std::sync::MutexGuard<'t3, ()>, (), impl std::future::Future}]>`
   = note: required because it appears within the type `impl std::future::Future`
   = note: required because it appears within the type `impl std::future::Future`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.

But on some other environment on CI, e.g. dist-i586-gnu-i586-i686-musl or Linux test-various, it emits it with a tiny difference:

14	   |
15	   = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `std::sync::MutexGuard<'_, ()>`
16	   = note: required because it appears within the type `for<'r, 's, 't0, 't1, 't2, 't3> {std::future::ResumeTy, std::sync::Arc<std::sync::Mutex<()>>, &'r std::sync::Mutex<()>, std::result::Result<std::sync::MutexGuard<'s, ()>, std::sync::PoisonError<std::sync::MutexGuard<'t0, ()>>>, &'t1 std::sync::MutexGuard<'t2, ()>, std::sync::MutexGuard<'t3, ()>, (), impl std::future::Future}`
-	   = note: required because it appears within the type `[static generator@DefId(15:11 ~ issue_67893[8787]::run[0]::{{closure}}[0]) for<'r, 's, 't0, 't1, 't2, 't3> {std::future::ResumeTy, std::sync::Arc<std::sync::Mutex<()>>, &'r std::sync::Mutex<()>, std::result::Result<std::sync::MutexGuard<'s, ()>, std::sync::PoisonError<std::sync::MutexGuard<'t0, ()>>>, &'t1 std::sync::MutexGuard<'t2, ()>, std::sync::MutexGuard<'t3, ()>, (), impl std::future::Future}]`
-	   = note: required because it appears within the type `std::future::from_generator::GenFuture<[static generator@DefId(15:11 ~ issue_67893[8787]::run[0]::{{closure}}[0]) for<'r, 's, 't0, 't1, 't2, 't3> {std::future::ResumeTy, std::sync::Arc<std::sync::Mutex<()>>, &'r std::sync::Mutex<()>, std::result::Result<std::sync::MutexGuard<'s, ()>, std::sync::PoisonError<std::sync::MutexGuard<'t0, ()>>>, &'t1 std::sync::MutexGuard<'t2, ()>, std::sync::MutexGuard<'t3, ()>, (), impl std::future::Future}]>`
+	   = note: required because it appears within the type `[static generator@DefId(14:11 ~ issue_67893[8787]::run[0]::{{closure}}[0]) for<'r, 's, 't0, 't1, 't2, 't3> {std::future::ResumeTy, std::sync::Arc<std::sync::Mutex<()>>, &'r std::sync::Mutex<()>, std::result::Result<std::sync::MutexGuard<'s, ()>, std::sync::PoisonError<std::sync::MutexGuard<'t0, ()>>>, &'t1 std::sync::MutexGuard<'t2, ()>, std::sync::MutexGuard<'t3, ()>, (), impl std::future::Future}]`
+	   = note: required because it appears within the type `std::future::from_generator::GenFuture<[static generator@DefId(14:11 ~ issue_67893[8787]::run[0]::{{closure}}[0]) for<'r, 's, 't0, 't1, 't2, 't3> {std::future::ResumeTy, std::sync::Arc<std::sync::Mutex<()>>, &'r std::sync::Mutex<()>, std::result::Result<std::sync::MutexGuard<'s, ()>, std::sync::PoisonError<std::sync::MutexGuard<'t0, ()>>>, &'t1 std::sync::MutexGuard<'t2, ()>, std::sync::MutexGuard<'t3, ()>, (), impl std::future::Future}]>`
19	   = note: required because it appears within the type `impl std::future::Future`
20	   = note: required because it appears within the type `impl std::future::Future`

It's ideal to have the same diagnostics on all the environment.

See also:

• Rollup of 5 pull requests #71190 (comment)
• Rollup of 4 pull requests #67556 (comment)

[estebank]

DefIds shouldn't be leaked in user output.

[JohnTitor]

Yeah, other places look like:

required because it appears within the type `[generator@$DIR/issue-68112.rs:48:20: 51:6 {impl std::ops::Generator, ()}]`

Perhaps we emit DefId accidentally in somewhere.

[estebank]

@JohnTitor that makes me think that we probably have some {:?} instead of {} somewhere.

[JohnTitor]

The relevant code is:

rust/src/librustc_trait_selection/traits/error_reporting/suggestions.rs

Lines 1633 to 1648 in ce93331

	ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
	let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
	let ty = parent_trait_ref.skip_binder().self_ty();
	err.note(&format!("required because it appears within the type `{}`", ty));
	obligated_types.push(ty);
	let parent_predicate = parent_trait_ref.without_const().to_predicate();
	if !self.is_recursive_obligation(obligated_types, &data.parent_code) {
	self.note_obligation_cause_code(
	err,
	&parent_predicate,
	&data.parent_code,
	obligated_types,
	);
	}
	}

I don't find any difference between here and similar places yet. @estebank thoughts?

[estebank]

@JohnTitor the place to look at is:

rust/src/librustc_middle/ty/print/pretty.rs

Lines 622 to 654 in 2deb39d

	// FIXME(eddyb) should use `def_span`.
	if let Some(hir_id) = self.tcx().hir().as_local_hir_id(did) {
	p!(write("@{:?}", self.tcx().hir().span(hir_id)));
	if substs.as_generator().is_valid() {
	let upvar_tys = substs.as_generator().upvar_tys();
	let mut sep = " ";
	for (&var_id, upvar_ty) in self
	.tcx()
	.upvars(did)
	.as_ref()
	.iter()
	.flat_map(|v| v.keys())
	.zip(upvar_tys)
	{
	p!(write("{}{}:", sep, self.tcx().hir().name(var_id)), print(upvar_ty));
	sep = ", ";
	}
	}
	} else {
	// Cross-crate closure types should only be
	// visible in codegen bug reports, I imagine.
	p!(write("@{:?}", did));
	if substs.as_generator().is_valid() {
	let upvar_tys = substs.as_generator().upvar_tys();
	let mut sep = " ";
	for (index, upvar_ty) in upvar_tys.enumerate() {
	p!(write("{}{}:", sep, index), print(upvar_ty));
	sep = ", ";
	}
	}
	}

CC @eddyb

The same applies to closures, but we are likely not displaying them this way anywhere (or we've just gotten lucky).