Account for type X = impl Trait; in lifetime suggestion

Author: estebank

src/librustc_mir/borrow_check/diagnostics/region_errors.rs

@@ -800,7 +800,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 // If there is a static predicate, then the only sensible suggestion is to replace
                 // fr with `'static`.
                 if has_static_predicate {
-                    diag.help(&format!("consider replacing `{}` with `{}`", fr_name, static_str,));
+                    diag.help(&format!("consider replacing `{}` with `{}`", fr_name, static_str));
                 } else {
                     // Otherwise, we should suggest adding a constraint on the return type.
                     let span = infcx.tcx.def_span(*did);
@@ -810,15 +810,20 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                         } else {
                             "'_".to_string()
                         };
-
+                        let suggestion = if snippet.ends_with(";") {
+                            // `type X = impl Trait;`
+                            format!("{} + {};", &snippet[..snippet.len() - 1], suggestable_fr_name)
+                        } else {
+                            format!("{} + {}", snippet, suggestable_fr_name)
+                        };
                         diag.span_suggestion(
                             span,
                             &format!(
                                 "to allow this `impl Trait` to capture borrowed data with lifetime \
                                  `{}`, add `{}` as a bound",
                                 fr_name, suggestable_fr_name,
                             ),
-                            format!("{} + {}", snippet, suggestable_fr_name),
+                            suggestion,
                             Applicability::MachineApplicable,
                         );
                     }

src/test/ui/impl-trait/multiple-lifetimes/error-handling.stderr

@@ -7,7 +7,7 @@ LL | fn foo<'a, 'b, 'c>(x: &'static i32, mut y: &'a i32) -> E<'b, 'c> {
    = help: consider replacing `'a` with `'static`
 help: to allow this `impl Trait` to capture borrowed data with lifetime `'a`, add `'a` as a bound
    |
-LL | type E<'a, 'b> = impl Sized; + 'a
+LL | type E<'a, 'b> = impl Sized + 'a;
    |
 
 error: aborting due to previous error