Pretty print lifetimes captured by RPIT

Author: compiler-errors

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -16,6 +16,7 @@ use rustc_session::cstore::{ExternCrate, ExternCrateSource};
 use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_target::abi::Size;
 use rustc_target::spec::abi::Abi;
+use smallvec::SmallVec;
 
 use std::cell::Cell;
 use std::char;
@@ -794,6 +795,7 @@ pub trait PrettyPrinter<'tcx>:
         let mut traits = FxIndexMap::default();
         let mut fn_traits = FxIndexMap::default();
         let mut is_sized = false;
+        let mut lifetimes = SmallVec::<[ty::Region<'tcx>; 1]>::new();
 
         for predicate in bounds.transpose_iter().map(|e| e.map_bound(|(p, _)| *p)) {
             let predicate = predicate.subst(tcx, substs);
@@ -825,6 +827,9 @@ pub trait PrettyPrinter<'tcx>:
                         &mut fn_traits,
                     );
                 }
+                ty::PredicateKind::TypeOutlives(outlives) => {
+                    lifetimes.push(outlives.1);
+                }
                 _ => {}
             }
         }
@@ -978,6 +983,17 @@ pub trait PrettyPrinter<'tcx>:
             write!(self, "Sized")?;
         }
 
+        if let [re] = lifetimes.as_slice()
+            && re.is_static()
+        {
+            // Don't print a single static lifetime
+        } else {
+            for re in lifetimes {
+                write!(self, " + ")?;
+                self = self.print_region(re)?;
+            }
+        }
+
         Ok(self)
     }
 

src/test/ui/impl-trait/hidden-lifetimes.stderr

@@ -1,4 +1,4 @@
-error[E0700]: hidden type for `impl Swap` captures lifetime that does not appear in bounds
+error[E0700]: hidden type for `impl Swap + 'a` captures lifetime that does not appear in bounds
   --> $DIR/hidden-lifetimes.rs:29:5
    |
 LL | fn hide_ref<'a, 'b, T: 'static>(x: &'a mut &'b T) -> impl Swap + 'a {
@@ -11,7 +11,7 @@ help: to declare that the `impl Trait` captures `'b`, you can add an explicit `'
 LL | fn hide_ref<'a, 'b, T: 'static>(x: &'a mut &'b T) -> impl Swap + 'a + 'b {
    |                                                                     ++++
 
-error[E0700]: hidden type for `impl Swap` captures lifetime that does not appear in bounds
+error[E0700]: hidden type for `impl Swap + 'a` captures lifetime that does not appear in bounds
   --> $DIR/hidden-lifetimes.rs:46:5
    |
 LL | fn hide_rc_refcell<'a, 'b: 'a, T: 'static>(x: Rc<RefCell<&'b T>>) -> impl Swap + 'a {