From 612657d9f0b158f0b78e85e3f0a694ddcbf83268 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Wed, 20 Jun 2018 15:38:07 -0700
Subject: [PATCH] Use lifetime name if available

---
 .../nice_region_error/static_impl_trait.rs           | 12 +++++++++---
 .../infer/error_reporting/nice_region_error/util.rs  |  2 +-
 .../impl-trait/static-return-lifetime-infered.stderr |  2 +-
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/librustc/infer/error_reporting/nice_region_error/static_impl_trait.rs b/src/librustc/infer/error_reporting/nice_region_error/static_impl_trait.rs
index bc6b7453c96e6..f9ec5fa13c960 100644
--- a/src/librustc/infer/error_reporting/nice_region_error/static_impl_trait.rs
+++ b/src/librustc/infer/error_reporting/nice_region_error/static_impl_trait.rs
@@ -12,7 +12,7 @@
 
 use infer::error_reporting::nice_region_error::NiceRegionError;
 use infer::lexical_region_resolve::RegionResolutionError;
-use ty::RegionKind;
+use ty::{BoundRegion, FreeRegion, RegionKind};
 use util::common::ErrorReported;
 
 impl<'a, 'gcx, 'tcx> NiceRegionError<'a, 'gcx, 'tcx> {
@@ -29,7 +29,7 @@ impl<'a, 'gcx, 'tcx> NiceRegionError<'a, 'gcx, 'tcx> {
                 ) => {
                     let anon_reg_sup = self.is_suitable_region(sup_r)?;
                     if sub_r == &RegionKind::ReStatic &&
-                        self._is_return_type_impl_trait(anon_reg_sup.def_id)
+                        self.is_return_type_impl_trait(anon_reg_sup.def_id)
                     {
                         let sp = var_origin.span();
                         let return_sp = sub_origin.span();
@@ -54,6 +54,12 @@ impl<'a, 'gcx, 'tcx> NiceRegionError<'a, 'gcx, 'tcx> {
                             );
                         }
 
+                        let lifetime_name = match sup_r {
+                            RegionKind::ReFree(FreeRegion {
+                                bound_region: BoundRegion::BrNamed(_, ref name), ..
+                            }) => format!("{}", name),
+                            _ => "'_".to_owned(),
+                        };
                         if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(return_sp) {
                             err.span_suggestion(
                                 return_sp,
@@ -62,7 +68,7 @@ impl<'a, 'gcx, 'tcx> NiceRegionError<'a, 'gcx, 'tcx> {
                                      less than `'static` and match {}",
                                     lifetime,
                                 ),
-                                format!("{} + '_", snippet),
+                                format!("{} + {}", snippet, lifetime_name),
                             );
                         }
                         err.emit();
diff --git a/src/librustc/infer/error_reporting/nice_region_error/util.rs b/src/librustc/infer/error_reporting/nice_region_error/util.rs
index 63e036166f8d7..1cc2b9d50b99b 100644
--- a/src/librustc/infer/error_reporting/nice_region_error/util.rs
+++ b/src/librustc/infer/error_reporting/nice_region_error/util.rs
@@ -168,7 +168,7 @@ impl<'a, 'gcx, 'tcx> NiceRegionError<'a, 'gcx, 'tcx> {
         None
     }
 
-    pub(super) fn _is_return_type_impl_trait(
+    pub(super) fn is_return_type_impl_trait(
         &self,
         scope_def_id: DefId,
     ) -> bool {
diff --git a/src/test/ui/impl-trait/static-return-lifetime-infered.stderr b/src/test/ui/impl-trait/static-return-lifetime-infered.stderr
index 06459ef66195b..2795bb92ed56f 100644
--- a/src/test/ui/impl-trait/static-return-lifetime-infered.stderr
+++ b/src/test/ui/impl-trait/static-return-lifetime-infered.stderr
@@ -37,7 +37,7 @@ LL |     fn iter_values<'a>(&'a self) -> impl Iterator<Item=u32> {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 help: you can add a constraint to the return type to make it last less than `'static` and match the lifetime 'a as defined on the method body at 20:5
    |
-LL |     fn iter_values<'a>(&'a self) -> impl Iterator<Item=u32> + '_ {
+LL |     fn iter_values<'a>(&'a self) -> impl Iterator<Item=u32> + 'a {
    |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 2 previous errors