account for the pick-constraint edges when reporting errors

Also, thread through better span info to improve the error message to
something tolerable.

2 files changed, 36 insertions, 0 deletions

diff --git a/src/test/ui/impl-trait/multiple-lifetimes/error-handling.rs b/src/test/ui/impl-trait/multiple-lifetimes/error-handling.rs
new file mode 100644
index 00000000000..b4cbf0ba8ed
--- /dev/null
+++ b/src/test/ui/impl-trait/multiple-lifetimes/error-handling.rs
@@ -0,0 +1,21 @@
+// compile-flags:-Zborrowck=mir
+
+#![feature(existential_type)]
+
+#[derive(Clone)]
+struct CopyIfEq<T, U>(T, U);
+
+impl<T: Copy> Copy for CopyIfEq<T, T> {}
+
+existential type E<'a, 'b>: Sized;
+//~^ ERROR lifetime may not live long enough
+
+fn foo<'a, 'b, 'c>(x: &'static i32, mut y: &'a i32) -> E<'b, 'c> {
+    let v = CopyIfEq::<*mut _, *mut _>(&mut {x}, &mut y);
+    let u = v;
+    let _: *mut &'a i32 = u.1;
+    unsafe { let _: &'b i32 = *u.0; }
+    u.0
+}
+
+fn main() {}
diff --git a/src/test/ui/impl-trait/multiple-lifetimes/error-handling.stderr b/src/test/ui/impl-trait/multiple-lifetimes/error-handling.stderr
new file mode 100644
index 00000000000..f42ec5b62f1
--- /dev/null
+++ b/src/test/ui/impl-trait/multiple-lifetimes/error-handling.stderr
@@ -0,0 +1,15 @@
+error: lifetime may not live long enough
+  --> $DIR/error-handling.rs:10:1
+   |
+LL | existential type E<'a, 'b>: Sized;
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ opaque type requires that `'a` must outlive `'static`
+...
+LL | fn foo<'a, 'b, 'c>(x: &'static i32, mut y: &'a i32) -> E<'b, 'c> {
+   |        -- lifetime `'a` defined here
+help: to allow this `impl Trait` to capture borrowed data with lifetime `'a`, add `'a` as a constraint
+   |
+LL | existential type E<'a, 'b>: Sized; + 'a
+   |
+
+error: aborting due to previous error
+