From 1e89b583c3bcf1757f57250a089450165e886049 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Sat, 1 May 2021 17:18:04 -0700
Subject: [PATCH] Account for unsatisfied bounds in E0599

Fix #84769, follow up to #84499, #83667.
---
 .../rustc_typeck/src/check/method/suggest.rs   |  6 +++++-
 .../import-trait-for-method-call.rs            |  9 ++++++++-
 .../import-trait-for-method-call.stderr        | 18 +++++++++++++++++-
 3 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_typeck/src/check/method/suggest.rs b/compiler/rustc_typeck/src/check/method/suggest.rs
index 73e35f0171aa7..b2e4e7a981d20 100644
--- a/compiler/rustc_typeck/src/check/method/suggest.rs
+++ b/compiler/rustc_typeck/src/check/method/suggest.rs
@@ -579,6 +579,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
 
                 let mut restrict_type_params = false;
+                let mut unsatisfied_bounds = false;
                 if !unsatisfied_predicates.is_empty() {
                     let def_span = |def_id| {
                         self.tcx.sess.source_map().guess_head_span(self.tcx.def_span(def_id))
@@ -739,6 +740,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         err.note(&format!(
                             "the following trait bounds were not satisfied:\n{bound_list}"
                         ));
+                        unsatisfied_bounds = true;
                     }
                 }
 
@@ -752,6 +754,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         source,
                         out_of_scope_traits,
                         &unsatisfied_predicates,
+                        unsatisfied_bounds,
                     );
                 }
 
@@ -984,9 +987,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         source: SelfSource<'tcx>,
         valid_out_of_scope_traits: Vec<DefId>,
         unsatisfied_predicates: &[(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)],
+        unsatisfied_bounds: bool,
     ) {
         let mut alt_rcvr_sugg = false;
-        if let SelfSource::MethodCall(rcvr) = source {
+        if let (SelfSource::MethodCall(rcvr), false) = (source, unsatisfied_bounds) {
             debug!(?span, ?item_name, ?rcvr_ty, ?rcvr);
             let skippable = [
                 self.tcx.lang_items().clone_trait(),
diff --git a/src/test/ui/suggestions/import-trait-for-method-call.rs b/src/test/ui/suggestions/import-trait-for-method-call.rs
index 646f68dea14e8..4dbadbdf98206 100644
--- a/src/test/ui/suggestions/import-trait-for-method-call.rs
+++ b/src/test/ui/suggestions/import-trait-for-method-call.rs
@@ -6,4 +6,11 @@ fn next_u64() -> u64 {
     h.finish() //~ ERROR no method named `finish` found for struct `DefaultHasher`
 }
 
-fn main() {}
+trait Bar {}
+impl Bar for String {}
+
+fn main() {
+    let s = String::from("hey");
+    let x: &dyn Bar = &s;
+    x.as_ref(); //~ ERROR the method `as_ref` exists for reference `&dyn Bar`, but its trait bounds
+}
diff --git a/src/test/ui/suggestions/import-trait-for-method-call.stderr b/src/test/ui/suggestions/import-trait-for-method-call.stderr
index f3ae20552f3d5..a2b9b9d14ab09 100644
--- a/src/test/ui/suggestions/import-trait-for-method-call.stderr
+++ b/src/test/ui/suggestions/import-trait-for-method-call.stderr
@@ -15,6 +15,22 @@ help: the following trait is implemented but not in scope; perhaps add a `use` f
 LL | use std::hash::Hasher;
    |
 
-error: aborting due to previous error
+error[E0599]: the method `as_ref` exists for reference `&dyn Bar`, but its trait bounds were not satisfied
+  --> $DIR/import-trait-for-method-call.rs:15:7
+   |
+LL | trait Bar {}
+   | --------- doesn't satisfy `dyn Bar: AsRef<_>`
+...
+LL |     x.as_ref();
+   |       ^^^^^^ method cannot be called on `&dyn Bar` due to unsatisfied trait bounds
+   |
+   = note: the following trait bounds were not satisfied:
+           `dyn Bar: AsRef<_>`
+           which is required by `&dyn Bar: AsRef<_>`
+   = help: items from traits can only be used if the trait is implemented and in scope
+   = note: the following trait defines an item `as_ref`, perhaps you need to implement it:
+           candidate #1: `AsRef`
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0599`.