Do not report _#nr lifetimes names in errors

Author: spastorino

src/librustc_mir/borrow_check/error_reporting.rs

@@ -497,14 +497,34 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
         _proper_span: Span,
         _end_span: Option<Span>,
     ) {
+        debug!(
+            "report_unscoped_local_value_does_not_live_long_enough(\
+                {:?}, {:?}, {:?}, {:?}, {:?}, {:?}\
+            )",
+            context,
+            name,
+            scope_tree,
+            borrow,
+            drop_span,
+            borrow_span
+        );
+
         let mut err = self.tcx.path_does_not_live_long_enough(borrow_span,
                                                               &format!("`{}`", name),
                                                               Origin::Mir);
         err.span_label(borrow_span, "borrowed value does not live long enough");
         err.span_label(drop_span, "borrowed value only lives until here");
-        self.tcx.note_and_explain_region(scope_tree, &mut err,
-                                         "borrowed value must be valid for ",
-                                         borrow.region, "...");
+
+        if !self.tcx.sess.nll() {
+            self.tcx.note_and_explain_region(
+                scope_tree,
+                &mut err,
+                "borrowed value must be valid for ",
+                borrow.region,
+                "...",
+            );
+        }
+
         self.explain_why_borrow_contains_point(context, borrow, &mut err);
         err.emit();
     }
@@ -519,14 +539,33 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
         proper_span: Span,
         _end_span: Option<Span>
     ) {
+        debug!(
+            "report_unscoped_temporary_value_does_not_live_long_enough(\
+                {:?}, {:?}, {:?}, {:?}, {:?}\
+            )",
+            context,
+            scope_tree,
+            borrow,
+            drop_span,
+            proper_span
+        );
+
         let mut err = self.tcx.path_does_not_live_long_enough(proper_span,
                                                               "borrowed value",
                                                               Origin::Mir);
         err.span_label(proper_span, "temporary value does not live long enough");
         err.span_label(drop_span, "temporary value only lives until here");
-        self.tcx.note_and_explain_region(scope_tree, &mut err,
-                                         "borrowed value must be valid for ",
-                                         borrow.region, "...");
+
+        if !self.tcx.sess.nll() {
+            self.tcx.note_and_explain_region(
+                scope_tree,
+                &mut err,
+                "borrowed value must be valid for ",
+                borrow.region,
+                "...",
+            );
+        }
+
         self.explain_why_borrow_contains_point(context, borrow, &mut err);
         err.emit();
     }

src/test/ui/nll/borrowed-local-error.rs

@@ -0,0 +1,26 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Znll-dump-cause
+
+#![feature(nll)]
+
+fn gimme(x: &(u32,)) -> &u32 {
+    &x.0
+}
+
+fn main() {
+    let x = gimme({
+        let v = (22,);
+        &v
+        //~^ ERROR `v` does not live long enough [E0597]
+    });
+    println!("{:?}", x);
+}

src/test/ui/nll/borrowed-local-error.stderr

@@ -0,0 +1,17 @@
+error[E0597]: `v` does not live long enough
+  --> $DIR/borrowed-local-error.rs:22:9
+   |
+LL |       let x = gimme({
+   |  _____________-
+LL | |         let v = (22,);
+LL | |         &v
+   | |         ^^ borrowed value does not live long enough
+LL | |         //~^ ERROR `v` does not live long enough [E0597]
+LL | |     });
+   | |_____-- borrow later used here
+   |       |
+   |       borrowed value only lives until here
+
+error: aborting due to previous error
+
+If you want more information on this error, try using "rustc --explain E0597"

src/test/ui/nll/borrowed-temporary-error.rs

@@ -0,0 +1,26 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Znll-dump-cause
+
+#![feature(nll)]
+
+fn gimme(x: &(u32,)) -> &u32 {
+    &x.0
+}
+
+fn main() {
+    let x = gimme({
+        let v = 22;
+        &(v,)
+        //~^ ERROR borrowed value does not live long enough [E0597]
+    });
+    println!("{:?}", x);
+}

src/test/ui/nll/borrowed-temporary-error.stderr

@@ -0,0 +1,14 @@
+error[E0597]: borrowed value does not live long enough
+  --> $DIR/borrowed-temporary-error.rs:22:10
+   |
+LL |         &(v,)
+   |          ^^^^ temporary value does not live long enough
+LL |         //~^ ERROR borrowed value does not live long enough [E0597]
+LL |     });
+   |       - temporary value only lives until here
+LL |     println!("{:?}", x);
+   |                      - borrow later used here
+
+error: aborting due to previous error
+
+If you want more information on this error, try using "rustc --explain E0597"