diff --git a/src/librustc_mir/borrow_check/diagnostics/region_errors.rs b/src/librustc_mir/borrow_check/diagnostics/region_errors.rs
index f1923b9e81c66..fa4846a20cbfb 100644
--- a/src/librustc_mir/borrow_check/diagnostics/region_errors.rs
+++ b/src/librustc_mir/borrow_check/diagnostics/region_errors.rs
@@ -122,7 +122,9 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
if self.regioncx.universal_regions().is_universal_region(r) {
Some(r)
} else {
- let upper_bound = self.regioncx.universal_upper_bound(r);
+ // We just want something nameable, even if it's not
+ // actually an upper bound.
+ let upper_bound = self.regioncx.approx_universal_upper_bound(r);
if self.regioncx.upper_bound_in_region_scc(r, upper_bound) {
self.to_error_region_vid(upper_bound)
diff --git a/src/librustc_mir/borrow_check/region_infer/mod.rs b/src/librustc_mir/borrow_check/region_infer/mod.rs
index 3e459bd52f757..081125cb625c2 100644
--- a/src/librustc_mir/borrow_check/region_infer/mod.rs
+++ b/src/librustc_mir/borrow_check/region_infer/mod.rs
@@ -1114,6 +1114,40 @@ impl<'tcx> RegionInferenceContext<'tcx> {
lub
}
+ /// Like `universal_upper_bound`, but returns an approximation more suitable
+ /// for diagnostics. If `r` contains multiple disjoint universal regions
+ /// (e.g. 'a and 'b in `fn foo<'a, 'b> { ... }`, we pick the lower-numbered region.
+ /// This corresponds to picking named regions over unnamed regions
+ /// (e.g. picking early-bound regions over a closure late-bound region).
+ ///
+ /// This means that the returned value may not be a true upper bound, since
+ /// only 'static is known to outlive disjoint universal regions.
+ /// Therefore, this method should only be used in diagnostic code,
+ /// where displaying *some* named universal region is better than
+ /// falling back to 'static.
+ pub(in crate::borrow_check) fn approx_universal_upper_bound(&self, r: RegionVid) -> RegionVid {
+ debug!("approx_universal_upper_bound(r={:?}={})", r, self.region_value_str(r));
+
+ // Find the smallest universal region that contains all other
+ // universal regions within `region`.
+ let mut lub = self.universal_regions.fr_fn_body;
+ let r_scc = self.constraint_sccs.scc(r);
+ let static_r = self.universal_regions.fr_static;
+ for ur in self.scc_values.universal_regions_outlived_by(r_scc) {
+ let new_lub = self.universal_region_relations.postdom_upper_bound(lub, ur);
+ debug!("approx_universal_upper_bound: ur={:?} lub={:?} new_lub={:?}", ur, lub, new_lub);
+ if ur != static_r && lub != static_r && new_lub == static_r {
+ lub = std::cmp::min(ur, lub);
+ } else {
+ lub = new_lub;
+ }
+ }
+
+ debug!("approx_universal_upper_bound: r={:?} lub={:?}", r, lub);
+
+ lub
+ }
+
/// Tests if `test` is true when applied to `lower_bound` at
/// `point`.
fn eval_verify_bound(
diff --git a/src/librustc_mir/borrow_check/region_infer/opaque_types.rs b/src/librustc_mir/borrow_check/region_infer/opaque_types.rs
index 7e352bfba77bc..325dca8c8ca99 100644
--- a/src/librustc_mir/borrow_check/region_infer/opaque_types.rs
+++ b/src/librustc_mir/borrow_check/region_infer/opaque_types.rs
@@ -141,7 +141,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
{
tcx.fold_regions(&ty, &mut false, |region, _| match *region {
ty::ReVar(vid) => {
- let upper_bound = self.universal_upper_bound(vid);
+ // Find something that we can name
+ let upper_bound = self.approx_universal_upper_bound(vid);
self.definitions[upper_bound].external_name.unwrap_or(region)
}
_ => region,
diff --git a/src/test/ui/async-await/issue-67765-async-diagnostic.rs b/src/test/ui/async-await/issue-67765-async-diagnostic.rs
new file mode 100644
index 0000000000000..5093916e73a45
--- /dev/null
+++ b/src/test/ui/async-await/issue-67765-async-diagnostic.rs
@@ -0,0 +1,16 @@
+// edition:2018
+//
+// Regression test for issue #67765
+// Tests that we point at the proper location when giving
+// a lifetime error.
+fn main() {}
+
+async fn func<'a>() -> Result<(), &'a str> {
+ let s = String::new();
+
+ let b = &s[..];
+
+ Err(b)?; //~ ERROR cannot return value referencing local variable `s`
+
+ Ok(())
+}
diff --git a/src/test/ui/async-await/issue-67765-async-diagnostic.stderr b/src/test/ui/async-await/issue-67765-async-diagnostic.stderr
new file mode 100644
index 0000000000000..78253042bee1c
--- /dev/null
+++ b/src/test/ui/async-await/issue-67765-async-diagnostic.stderr
@@ -0,0 +1,12 @@
+error[E0515]: cannot return value referencing local variable `s`
+ --> $DIR/issue-67765-async-diagnostic.rs:13:11
+ |
+LL | let b = &s[..];
+ | - `s` is borrowed here
+LL |
+LL | Err(b)?;
+ | ^ returns a value referencing data owned by the current function
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0515`.
diff --git a/src/test/ui/lifetimes/unnamed-closure-doesnt-life-long-enough-issue-67634.rs b/src/test/ui/lifetimes/unnamed-closure-doesnt-life-long-enough-issue-67634.rs
index 19d7f0190479e..8deb365515840 100644
--- a/src/test/ui/lifetimes/unnamed-closure-doesnt-life-long-enough-issue-67634.rs
+++ b/src/test/ui/lifetimes/unnamed-closure-doesnt-life-long-enough-issue-67634.rs
@@ -1,3 +1,3 @@
fn main() {
- [0].iter().flat_map(|a| [0].iter().map(|_| &a)); //~ ERROR `a` does not live long enough
+ [0].iter().flat_map(|a| [0].iter().map(|_| &a)); //~ ERROR closure may outlive
}
diff --git a/src/test/ui/lifetimes/unnamed-closure-doesnt-life-long-enough-issue-67634.stderr b/src/test/ui/lifetimes/unnamed-closure-doesnt-life-long-enough-issue-67634.stderr
index cb0b481e74876..34470119112fb 100644
--- a/src/test/ui/lifetimes/unnamed-closure-doesnt-life-long-enough-issue-67634.stderr
+++ b/src/test/ui/lifetimes/unnamed-closure-doesnt-life-long-enough-issue-67634.stderr
@@ -1,15 +1,21 @@
-error[E0597]: `a` does not live long enough
- --> $DIR/unnamed-closure-doesnt-life-long-enough-issue-67634.rs:2:49
+error[E0373]: closure may outlive the current function, but it borrows `a`, which is owned by the current function
+ --> $DIR/unnamed-closure-doesnt-life-long-enough-issue-67634.rs:2:44
|
LL | [0].iter().flat_map(|a| [0].iter().map(|_| &a));
- | - ^- ...but `a` will be dropped here, when the enclosing closure returns
- | | |
- | | `a` would have to be valid for `'_`...
- | has type `&i32`
+ | ^^^ - `a` is borrowed here
+ | |
+ | may outlive borrowed value `a`
|
- = note: functions cannot return a borrow to data owned within the function's scope, functions can only return borrows to data passed as arguments
- = note: to learn more, visit <https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html#dangling-references>
+note: closure is returned here
+ --> $DIR/unnamed-closure-doesnt-life-long-enough-issue-67634.rs:2:29
+ |
+LL | [0].iter().flat_map(|a| [0].iter().map(|_| &a));
+ | ^^^^^^^^^^^^^^^^^^^^^^
+help: to force the closure to take ownership of `a` (and any other referenced variables), use the `move` keyword
+ |
+LL | [0].iter().flat_map(|a| [0].iter().map(move |_| &a));
+ | ^^^^^^^^
error: aborting due to previous error
-For more information about this error, try `rustc --explain E0597`.
+For more information about this error, try `rustc --explain E0373`.
diff --git a/src/test/ui/return-disjoint-regions.rs b/src/test/ui/return-disjoint-regions.rs
new file mode 100644
index 0000000000000..d0feb3b65e12a
--- /dev/null
+++ b/src/test/ui/return-disjoint-regions.rs
@@ -0,0 +1,7 @@
+// See https://github.com/rust-lang/rust/pull/67911#issuecomment-576023915
+fn f<'a, 'b>(x: i32) -> (&'a i32, &'b i32) {
+ let y = &x;
+ (y, y) //~ ERROR cannot return
+}
+
+fn main() {}
diff --git a/src/test/ui/return-disjoint-regions.stderr b/src/test/ui/return-disjoint-regions.stderr
new file mode 100644
index 0000000000000..ed159298804ae
--- /dev/null
+++ b/src/test/ui/return-disjoint-regions.stderr
@@ -0,0 +1,11 @@
+error[E0515]: cannot return value referencing function parameter `x`
+ --> $DIR/return-disjoint-regions.rs:4:5
+ |
+LL | let y = &x;
+ | -- `x` is borrowed here
+LL | (y, y)
+ | ^^^^^^ returns a value referencing data owned by the current function
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0515`.