From 5cccb36cfbc887da04dc367c24d2b4947c993ff9 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sun, 18 Dec 2022 03:04:21 +0000
Subject: higher-ranked lifetime message

---
 compiler/rustc_resolve/src/late.rs | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

(limited to 'compiler/rustc_resolve/src')

diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 5b7a00101e9..ef0f41223ea 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -1512,7 +1512,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             count: 1,
         };
         let elision_candidate = LifetimeElisionCandidate::Missing(missing_lifetime);
-        for rib in self.lifetime_ribs.iter().rev() {
+        for (i, rib) in self.lifetime_ribs.iter().enumerate().rev() {
             debug!(?rib.kind);
             match rib.kind {
                 LifetimeRibKind::AnonymousCreateParameter { binder, .. } => {
@@ -1529,16 +1529,31 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                     } else {
                         ("`'_` cannot be used here", "`'_` is a reserved lifetime name")
                     };
-                    rustc_errors::struct_span_err!(
+                    let mut diag = rustc_errors::struct_span_err!(
                         self.r.session,
                         lifetime.ident.span,
                         E0637,
                         "{}",
                         msg,
-                    )
-                    .span_label(lifetime.ident.span, note)
-                    .emit();
-
+                    );
+                    diag.span_label(lifetime.ident.span, note);
+                    if elided {
+                        for rib in self.lifetime_ribs[i..].iter().rev() {
+                            if let LifetimeRibKind::Generics {
+                                span,
+                                kind: LifetimeBinderKind::PolyTrait | LifetimeBinderKind::WhereBound,
+                                ..
+                            } = &rib.kind
+                            {
+                                diag.span_help(
+                                    *span,
+                                    "consider introducing a higher-ranked lifetime here with `for<'a>`",
+                                );
+                                break;
+                            }
+                        }
+                    }
+                    diag.emit();
                     self.record_lifetime_res(lifetime.id, LifetimeRes::Error, elision_candidate);
                     return;
                 }
-- 
cgit 1.4.1-3-g733a5