From b9235ea57c460ef4c2f2b963d85f3040c7e09398 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Wed, 12 Dec 2018 13:57:47 -0800
Subject: [PATCH] Account for `impl Trait` when suggesting lifetime

---
 src/librustc/infer/error_reporting/mod.rs     | 31 ++++++++++++-------
 .../suggest-impl-trait-lifetime.fixed         | 18 +++++++++++
 .../suggest-impl-trait-lifetime.rs            | 18 +++++++++++
 .../suggest-impl-trait-lifetime.stderr        | 19 ++++++++++++
 4 files changed, 75 insertions(+), 11 deletions(-)
 create mode 100644 src/test/ui/suggestions/suggest-impl-trait-lifetime.fixed
 create mode 100644 src/test/ui/suggestions/suggest-impl-trait-lifetime.rs
 create mode 100644 src/test/ui/suggestions/suggest-impl-trait-lifetime.stderr

diff --git a/src/librustc/infer/error_reporting/mod.rs b/src/librustc/infer/error_reporting/mod.rs
index 7d997a0154600..d213a5c561871 100644
--- a/src/librustc/infer/error_reporting/mod.rs
+++ b/src/librustc/infer/error_reporting/mod.rs
@@ -1095,7 +1095,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                             let sp = hir.span(id);
                             // `sp` only covers `T`, change it so that it covers
                             // `T:` when appropriate
-                            let sp = if has_bounds {
+                            let is_impl_trait = bound_kind.to_string().starts_with("impl ");
+                            let sp = if has_bounds && !is_impl_trait {
                                 sp.to(self.tcx
                                     .sess
                                     .source_map()
@@ -1103,7 +1104,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                             } else {
                                 sp
                             };
-                            (sp, has_bounds)
+                            (sp, has_bounds, is_impl_trait)
                         })
                     } else {
                         None
@@ -1136,25 +1137,33 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 
         fn binding_suggestion<'tcx, S: fmt::Display>(
             err: &mut DiagnosticBuilder<'tcx>,
-            type_param_span: Option<(Span, bool)>,
+            type_param_span: Option<(Span, bool, bool)>,
             bound_kind: GenericKind<'tcx>,
             sub: S,
         ) {
-            let consider = &format!(
-                "consider adding an explicit lifetime bound `{}: {}`...",
-                bound_kind, sub
+            let consider = format!(
+                "consider adding an explicit lifetime bound {}",
+                if type_param_span.map(|(_, _, is_impl_trait)| is_impl_trait).unwrap_or(false) {
+                    format!(" `{}` to `{}`...", sub, bound_kind)
+                } else {
+                    format!("`{}: {}`...", bound_kind, sub)
+                },
             );
-            if let Some((sp, has_lifetimes)) = type_param_span {
-                let tail = if has_lifetimes { " + " } else { "" };
-                let suggestion = format!("{}: {}{}", bound_kind, sub, tail);
+            if let Some((sp, has_lifetimes, is_impl_trait)) = type_param_span {
+                let suggestion = if is_impl_trait {
+                    format!("{} + {}", bound_kind, sub)
+                } else {
+                    let tail = if has_lifetimes { " + " } else { "" };
+                    format!("{}: {}{}", bound_kind, sub, tail)
+                };
                 err.span_suggestion_short_with_applicability(
                     sp,
-                    consider,
+                    &consider,
                     suggestion,
                     Applicability::MaybeIncorrect, // Issue #41966
                 );
             } else {
-                err.help(consider);
+                err.help(&consider);
             }
         }
 
diff --git a/src/test/ui/suggestions/suggest-impl-trait-lifetime.fixed b/src/test/ui/suggestions/suggest-impl-trait-lifetime.fixed
new file mode 100644
index 0000000000000..8592af1262e6f
--- /dev/null
+++ b/src/test/ui/suggestions/suggest-impl-trait-lifetime.fixed
@@ -0,0 +1,18 @@
+// run-rustfix
+
+use std::fmt::Debug;
+
+fn foo(d: impl Debug + 'static) {
+//~^ HELP consider adding an explicit lifetime bound  `'static` to `impl Debug`
+    bar(d);
+//~^ ERROR the parameter type `impl Debug` may not live long enough
+//~| NOTE ...so that the type `impl Debug` will meet its required lifetime bounds
+}
+
+fn bar(d: impl Debug + 'static) {
+    println!("{:?}", d)
+}
+
+fn main() {
+  foo("hi");
+}
diff --git a/src/test/ui/suggestions/suggest-impl-trait-lifetime.rs b/src/test/ui/suggestions/suggest-impl-trait-lifetime.rs
new file mode 100644
index 0000000000000..c67d78ea4c73b
--- /dev/null
+++ b/src/test/ui/suggestions/suggest-impl-trait-lifetime.rs
@@ -0,0 +1,18 @@
+// run-rustfix
+
+use std::fmt::Debug;
+
+fn foo(d: impl Debug) {
+//~^ HELP consider adding an explicit lifetime bound  `'static` to `impl Debug`
+    bar(d);
+//~^ ERROR the parameter type `impl Debug` may not live long enough
+//~| NOTE ...so that the type `impl Debug` will meet its required lifetime bounds
+}
+
+fn bar(d: impl Debug + 'static) {
+    println!("{:?}", d)
+}
+
+fn main() {
+  foo("hi");
+}
diff --git a/src/test/ui/suggestions/suggest-impl-trait-lifetime.stderr b/src/test/ui/suggestions/suggest-impl-trait-lifetime.stderr
new file mode 100644
index 0000000000000..cba231d0e86e5
--- /dev/null
+++ b/src/test/ui/suggestions/suggest-impl-trait-lifetime.stderr
@@ -0,0 +1,19 @@
+error[E0310]: the parameter type `impl Debug` may not live long enough
+  --> $DIR/suggest-impl-trait-lifetime.rs:7:5
+   |
+LL |     bar(d);
+   |     ^^^
+   |
+note: ...so that the type `impl Debug` will meet its required lifetime bounds
+  --> $DIR/suggest-impl-trait-lifetime.rs:7:5
+   |
+LL |     bar(d);
+   |     ^^^
+help: consider adding an explicit lifetime bound  `'static` to `impl Debug`...
+   |
+LL | fn foo(d: impl Debug + 'static) {
+   |           ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0310`.