From d67628e053db3235b9d4d406e4b47113b51a1fad Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Mon, 14 May 2018 23:32:21 -0700
Subject: [PATCH 01/15] Add lint checks for unused loop labels

---
 src/librustc_lint/lib.rs                   |  4 +-
 src/librustc_lint/unused.rs                | 63 ++++++++++++++++++++++
 src/librustc_mir/interpret/eval_context.rs |  2 +-
 src/test/ui/lint/unused_loop_label.rs      | 55 +++++++++++++++++++
 src/test/ui/lint/unused_loop_label.stderr  | 32 +++++++++++
 src/test/ui/lint/unused_loop_label.stdout  |  0
 6 files changed, 154 insertions(+), 2 deletions(-)
 create mode 100644 src/test/ui/lint/unused_loop_label.rs
 create mode 100644 src/test/ui/lint/unused_loop_label.stderr
 create mode 100644 src/test/ui/lint/unused_loop_label.stdout

diff --git a/src/librustc_lint/lib.rs b/src/librustc_lint/lib.rs
index 0ae133640fad9..19e0bbd830530 100644
--- a/src/librustc_lint/lib.rs
+++ b/src/librustc_lint/lib.rs
@@ -110,6 +110,7 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
 
     add_early_builtin_with_new!(sess,
                                 DeprecatedAttr,
+                                UnusedLoopLabel,
                                 );
 
     add_builtin!(sess,
@@ -177,7 +178,8 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
                     UNUSED_DOC_COMMENT,
                     UNUSED_EXTERN_CRATES,
                     UNUSED_FEATURES,
-                    UNUSED_PARENS);
+                    UNUSED_PARENS,
+                    UNUSED_LOOP_LABEL);
 
     add_lint_group!(sess,
                     "rust_2018_idioms",
diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index 845c964b986dd..38c5a36067c46 100644
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -25,6 +25,8 @@ use syntax_pos::Span;
 
 use rustc::hir;
 
+use std::vec;
+
 declare_lint! {
     pub UNUSED_MUST_USE,
     Warn,
@@ -464,3 +466,64 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation {
         }
     }
 }
+
+declare_lint! {
+    pub(super) UNUSED_LOOP_LABEL,
+    Warn,
+    "warns on unused labels for loops"
+}
+
+#[derive(Clone)]
+pub struct UnusedLoopLabel(pub vec::Vec<ast::Label>);
+
+impl UnusedLoopLabel {
+    pub fn new() -> Self {
+        UnusedLoopLabel(vec![])
+    }
+}
+
+impl LintPass for UnusedLoopLabel {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(UNUSED_LOOP_LABEL)
+    }
+}
+
+impl EarlyLintPass for UnusedLoopLabel {
+    fn check_expr(&mut self, _: &EarlyContext, expr: &ast::Expr) {
+        match expr.node {
+            ast::ExprKind::While(_, _, Some(ref label))
+            | ast::ExprKind::WhileLet(_, _, _, Some(ref label))
+            | ast::ExprKind::ForLoop(_, _, _, Some(ref label))
+            | ast::ExprKind::Loop(_, Some(ref label)) => {
+                self.0.push(*label);
+            }
+            ast::ExprKind::Break(Some(ref label), _) | ast::ExprKind::Continue(Some(ref label)) => {
+                'remove_used_label: for i in (0..self.0.len()).rev() {
+                    if self.0.get(i).unwrap().ident.name == label.ident.name {
+                        self.0.remove(i);
+                        break 'remove_used_label;
+                    }
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn check_expr_post(&mut self, ctxt: &EarlyContext, expr: &ast::Expr) {
+        match expr.node {
+            ast::ExprKind::While(_, _, Some(ref label))
+            | ast::ExprKind::WhileLet(_, _, _, Some(ref label))
+            | ast::ExprKind::ForLoop(_, _, _, Some(ref label))
+            | ast::ExprKind::Loop(_, Some(ref label)) => if !self.0.is_empty() {
+                {
+                    let unused_label = self.0.last().unwrap();
+                    if label.ident.name == unused_label.ident.name {
+                        ctxt.span_lint(UNUSED_LOOP_LABEL, label.ident.span, "unused loop label");
+                    }
+                }
+                self.0.pop();
+            },
+            _ => {}
+        }
+    }
+}
diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index 03137619edaf4..7b6cee96a875c 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -1705,7 +1705,7 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M
             let mut trace_text = "\n\nAn error occurred in miri:\n".to_string();
             backtrace.resolve();
             write!(trace_text, "backtrace frames: {}\n", backtrace.frames().len()).unwrap();
-            'frames: for (i, frame) in backtrace.frames().iter().enumerate() {
+            for (i, frame) in backtrace.frames().iter().enumerate() {
                 if frame.symbols().is_empty() {
                     write!(trace_text, "{}: no symbols\n", i).unwrap();
                 }
diff --git a/src/test/ui/lint/unused_loop_label.rs b/src/test/ui/lint/unused_loop_label.rs
new file mode 100644
index 0000000000000..b3142cd863375
--- /dev/null
+++ b/src/test/ui/lint/unused_loop_label.rs
@@ -0,0 +1,55 @@
+// Copyright 2017 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.
+
+// The output should warn when a loop label is not used. However, it
+// should also deal with the edge cases where a label is shadowed,
+// within nested loops
+
+// compile-pass
+// compile-flags: -W unused_loop_label
+
+fn main() {
+    'unused_while_label: while 0 == 0 {
+        //~^ WARN unused loop label
+    }
+
+    let opt = Some(0);
+    'unused_while_let_label: while let Some(_) = opt {
+        //~^ WARN unused loop label
+    }
+
+    'unused_for_label: for _ in 0..10 {
+        //~^ WARN unused loop label
+    }
+
+    'used_loop_label: loop {
+        break 'used_loop_label;
+    }
+
+    'used_loop_label_outer: loop {
+        'used_loop_label_inner: loop {
+            break 'used_loop_label_inner;
+        }
+        break 'used_loop_label_outer;
+    }
+
+    'unused_loop_label_outer: loop {
+        'unused_loop_label_inner: loop {
+            //~^ WARN unused loop label
+            break 'unused_loop_label_outer;
+        }
+    }
+
+    // This is diverging, so put it at the end so we don't get unreachable_code errors everywhere
+    // else
+    'unused_loop_label: loop {
+        //~^ WARN unused loop label
+    }
+}
diff --git a/src/test/ui/lint/unused_loop_label.stderr b/src/test/ui/lint/unused_loop_label.stderr
new file mode 100644
index 0000000000000..4804c268975f7
--- /dev/null
+++ b/src/test/ui/lint/unused_loop_label.stderr
@@ -0,0 +1,32 @@
+warning: unused loop label
+  --> $DIR/unused_loop_label.rs:19:5
+   |
+LL |     'unused_while_label: while 0 == 0 {
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: requested on the command line with `-W unused-loop-label`
+
+warning: unused loop label
+  --> $DIR/unused_loop_label.rs:24:5
+   |
+LL |     'unused_while_let_label: while let Some(_) = opt {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: unused loop label
+  --> $DIR/unused_loop_label.rs:28:5
+   |
+LL |     'unused_for_label: for _ in 0..10 {
+   |     ^^^^^^^^^^^^^^^^^
+
+warning: unused loop label
+  --> $DIR/unused_loop_label.rs:44:9
+   |
+LL |         'unused_loop_label_inner: loop {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: unused loop label
+  --> $DIR/unused_loop_label.rs:52:5
+   |
+LL |     'unused_loop_label: loop {
+   |     ^^^^^^^^^^^^^^^^^^
+
diff --git a/src/test/ui/lint/unused_loop_label.stdout b/src/test/ui/lint/unused_loop_label.stdout
new file mode 100644
index 0000000000000..e69de29bb2d1d

From 7c4aa7362e9bca54e5bb4f96cc67b4aafe35b33a Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Tue, 15 May 2018 16:34:08 -0700
Subject: [PATCH 02/15] Rename test to `unused_label` and remove empty `stdout`
 file

---
 src/test/ui/lint/{unused_loop_label.rs => unused_label.rs}        | 0
 .../ui/lint/{unused_loop_label.stderr => unused_label.stderr}     | 0
 src/test/ui/lint/unused_loop_label.stdout                         | 0
 3 files changed, 0 insertions(+), 0 deletions(-)
 rename src/test/ui/lint/{unused_loop_label.rs => unused_label.rs} (100%)
 rename src/test/ui/lint/{unused_loop_label.stderr => unused_label.stderr} (100%)
 delete mode 100644 src/test/ui/lint/unused_loop_label.stdout

diff --git a/src/test/ui/lint/unused_loop_label.rs b/src/test/ui/lint/unused_label.rs
similarity index 100%
rename from src/test/ui/lint/unused_loop_label.rs
rename to src/test/ui/lint/unused_label.rs
diff --git a/src/test/ui/lint/unused_loop_label.stderr b/src/test/ui/lint/unused_label.stderr
similarity index 100%
rename from src/test/ui/lint/unused_loop_label.stderr
rename to src/test/ui/lint/unused_label.stderr
diff --git a/src/test/ui/lint/unused_loop_label.stdout b/src/test/ui/lint/unused_loop_label.stdout
deleted file mode 100644
index e69de29bb2d1d..0000000000000

From bb867d3512b009c660f8a9c3154d19e119f7ff5d Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Tue, 15 May 2018 17:08:24 -0700
Subject: [PATCH 03/15] Add additional test case to unused_label lint

---
 src/test/ui/lint/unused_label.rs     | 25 ++++++++++++++--------
 src/test/ui/lint/unused_label.stderr | 32 +++++++++++++++++-----------
 2 files changed, 35 insertions(+), 22 deletions(-)

diff --git a/src/test/ui/lint/unused_label.rs b/src/test/ui/lint/unused_label.rs
index b3142cd863375..43cf8c75ae3f0 100644
--- a/src/test/ui/lint/unused_label.rs
+++ b/src/test/ui/lint/unused_label.rs
@@ -33,22 +33,29 @@ fn main() {
         break 'used_loop_label;
     }
 
-    'used_loop_label_outer: loop {
-        'used_loop_label_inner: loop {
-            break 'used_loop_label_inner;
+    'used_loop_label_outer_1: loop {
+        'used_loop_label_inner_1: loop {
+            break 'used_loop_label_inner_1;
         }
-        break 'used_loop_label_outer;
+        break 'used_loop_label_outer_1;
     }
 
-    'unused_loop_label_outer: loop {
-        'unused_loop_label_inner: loop {
+    'used_loop_label_outer_2: loop {
+        'unused_loop_label_inner_2: loop {
             //~^ WARN unused loop label
-            break 'unused_loop_label_outer;
+            break 'used_loop_label_outer_2;
         }
     }
 
-    // This is diverging, so put it at the end so we don't get unreachable_code errors everywhere
-    // else
+    'unused_loop_label_outer_3: loop {
+        'used_loop_label_inner_3: loop {
+            //~^ WARN unused loop label
+            break 'used_loop_label_inner_3;
+        }
+    }
+
+    // This is diverging, so put it at the end so we don't get
+    // unreachable_code errors everywhere else
     'unused_loop_label: loop {
         //~^ WARN unused loop label
     }
diff --git a/src/test/ui/lint/unused_label.stderr b/src/test/ui/lint/unused_label.stderr
index 4804c268975f7..3e7be476e6439 100644
--- a/src/test/ui/lint/unused_label.stderr
+++ b/src/test/ui/lint/unused_label.stderr
@@ -1,31 +1,37 @@
-warning: unused loop label
-  --> $DIR/unused_loop_label.rs:19:5
+warning: unused label
+  --> $DIR/unused_label.rs:19:5
    |
 LL |     'unused_while_label: while 0 == 0 {
    |     ^^^^^^^^^^^^^^^^^^^
    |
-   = note: requested on the command line with `-W unused-loop-label`
+   = note: requested on the command line with `-W unused-label`
 
-warning: unused loop label
-  --> $DIR/unused_loop_label.rs:24:5
+warning: unused label
+  --> $DIR/unused_label.rs:24:5
    |
 LL |     'unused_while_let_label: while let Some(_) = opt {
    |     ^^^^^^^^^^^^^^^^^^^^^^^
 
-warning: unused loop label
-  --> $DIR/unused_loop_label.rs:28:5
+warning: unused label
+  --> $DIR/unused_label.rs:28:5
    |
 LL |     'unused_for_label: for _ in 0..10 {
    |     ^^^^^^^^^^^^^^^^^
 
-warning: unused loop label
-  --> $DIR/unused_loop_label.rs:44:9
+warning: unused label
+  --> $DIR/unused_label.rs:44:9
    |
-LL |         'unused_loop_label_inner: loop {
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         'unused_loop_label_inner_2: loop {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-warning: unused loop label
-  --> $DIR/unused_loop_label.rs:52:5
+warning: unused label
+  --> $DIR/unused_label.rs:50:9
+   |
+LL |     'unused_loop_label_outer_3: loop {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: unused label
+  --> $DIR/unused_label.rs:52:5
    |
 LL |     'unused_loop_label: loop {
    |     ^^^^^^^^^^^^^^^^^^

From acd6ab8f0f00365b424ac9cd83d9d08852add0bc Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Tue, 15 May 2018 17:36:43 -0700
Subject: [PATCH 04/15] Rename `unused_loop_label` to `unused_label` and
 fix/clean up lint logic

---
 src/librustc_lint/lib.rs             |  6 +--
 src/librustc_lint/unused.rs          | 55 +++++++++++++---------------
 src/test/ui/lint/unused_label.rs     | 14 +++----
 src/test/ui/lint/unused_label.stderr |  4 +-
 4 files changed, 37 insertions(+), 42 deletions(-)

diff --git a/src/librustc_lint/lib.rs b/src/librustc_lint/lib.rs
index 19e0bbd830530..b0a766ec05874 100644
--- a/src/librustc_lint/lib.rs
+++ b/src/librustc_lint/lib.rs
@@ -110,7 +110,7 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
 
     add_early_builtin_with_new!(sess,
                                 DeprecatedAttr,
-                                UnusedLoopLabel,
+                                UnusedLabel,
                                 );
 
     add_builtin!(sess,
@@ -178,8 +178,8 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
                     UNUSED_DOC_COMMENT,
                     UNUSED_EXTERN_CRATES,
                     UNUSED_FEATURES,
-                    UNUSED_PARENS,
-                    UNUSED_LOOP_LABEL);
+                    UNUSED_LABEL,
+                    UNUSED_PARENS);
 
     add_lint_group!(sess,
                     "rust_2018_idioms",
diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index 38c5a36067c46..61c0485f88615 100644
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -25,8 +25,6 @@ use syntax_pos::Span;
 
 use rustc::hir;
 
-use std::vec;
-
 declare_lint! {
     pub UNUSED_MUST_USE,
     Warn,
@@ -468,41 +466,38 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation {
 }
 
 declare_lint! {
-    pub(super) UNUSED_LOOP_LABEL,
+    pub(super) UNUSED_LABEL,
     Warn,
-    "warns on unused labels for loops"
+    "warns on unused labels"
 }
 
 #[derive(Clone)]
-pub struct UnusedLoopLabel(pub vec::Vec<ast::Label>);
+pub struct UnusedLabel(pub Vec<ast::Label>);
 
-impl UnusedLoopLabel {
+impl UnusedLabel {
     pub fn new() -> Self {
-        UnusedLoopLabel(vec![])
+        UnusedLabel(vec![])
     }
 }
 
-impl LintPass for UnusedLoopLabel {
+impl LintPass for UnusedLabel {
     fn get_lints(&self) -> LintArray {
-        lint_array!(UNUSED_LOOP_LABEL)
+        lint_array!(UNUSED_LABEL)
     }
 }
 
-impl EarlyLintPass for UnusedLoopLabel {
+impl EarlyLintPass for UnusedLabel {
     fn check_expr(&mut self, _: &EarlyContext, expr: &ast::Expr) {
         match expr.node {
-            ast::ExprKind::While(_, _, Some(ref label))
-            | ast::ExprKind::WhileLet(_, _, _, Some(ref label))
-            | ast::ExprKind::ForLoop(_, _, _, Some(ref label))
-            | ast::ExprKind::Loop(_, Some(ref label)) => {
-                self.0.push(*label);
+            ast::ExprKind::While(_, _, Some(label))
+            | ast::ExprKind::WhileLet(_, _, _, Some(label))
+            | ast::ExprKind::ForLoop(_, _, _, Some(label))
+            | ast::ExprKind::Loop(_, Some(label)) => {
+                self.0.push(label);
             }
-            ast::ExprKind::Break(Some(ref label), _) | ast::ExprKind::Continue(Some(ref label)) => {
-                'remove_used_label: for i in (0..self.0.len()).rev() {
-                    if self.0.get(i).unwrap().ident.name == label.ident.name {
-                        self.0.remove(i);
-                        break 'remove_used_label;
-                    }
+            ast::ExprKind::Break(Some(label), _) | ast::ExprKind::Continue(Some(label)) => {
+                if let Some(index) = self.0.iter().rposition(|&l| l.ident == label.ident) {
+                    self.0.remove(index);
                 }
             }
             _ => {}
@@ -511,17 +506,17 @@ impl EarlyLintPass for UnusedLoopLabel {
 
     fn check_expr_post(&mut self, ctxt: &EarlyContext, expr: &ast::Expr) {
         match expr.node {
-            ast::ExprKind::While(_, _, Some(ref label))
-            | ast::ExprKind::WhileLet(_, _, _, Some(ref label))
-            | ast::ExprKind::ForLoop(_, _, _, Some(ref label))
-            | ast::ExprKind::Loop(_, Some(ref label)) => if !self.0.is_empty() {
-                {
-                    let unused_label = self.0.last().unwrap();
-                    if label.ident.name == unused_label.ident.name {
-                        ctxt.span_lint(UNUSED_LOOP_LABEL, label.ident.span, "unused loop label");
+            ast::ExprKind::While(_, _, Some(label))
+            | ast::ExprKind::WhileLet(_, _, _, Some(label))
+            | ast::ExprKind::ForLoop(_, _, _, Some(label))
+            | ast::ExprKind::Loop(_, Some(label)) => {
+                if let Some(unused_label) = self.0.pop() {
+                    if label.ident == unused_label.ident {
+                        ctxt.span_lint(UNUSED_LABEL, label.ident.span, "unused label");
+                    } else {
+                        self.0.push(unused_label);
                     }
                 }
-                self.0.pop();
             },
             _ => {}
         }
diff --git a/src/test/ui/lint/unused_label.rs b/src/test/ui/lint/unused_label.rs
index 43cf8c75ae3f0..ceb70fc542dc0 100644
--- a/src/test/ui/lint/unused_label.rs
+++ b/src/test/ui/lint/unused_label.rs
@@ -13,20 +13,20 @@
 // within nested loops
 
 // compile-pass
-// compile-flags: -W unused_loop_label
+// compile-flags: -W unused-label
 
 fn main() {
     'unused_while_label: while 0 == 0 {
-        //~^ WARN unused loop label
+        //~^ WARN unused label
     }
 
     let opt = Some(0);
     'unused_while_let_label: while let Some(_) = opt {
-        //~^ WARN unused loop label
+        //~^ WARN unused label
     }
 
     'unused_for_label: for _ in 0..10 {
-        //~^ WARN unused loop label
+        //~^ WARN unused label
     }
 
     'used_loop_label: loop {
@@ -42,14 +42,14 @@ fn main() {
 
     'used_loop_label_outer_2: loop {
         'unused_loop_label_inner_2: loop {
-            //~^ WARN unused loop label
+            //~^ WARN unused label
             break 'used_loop_label_outer_2;
         }
     }
 
     'unused_loop_label_outer_3: loop {
+        //~^ WARN unused label
         'used_loop_label_inner_3: loop {
-            //~^ WARN unused loop label
             break 'used_loop_label_inner_3;
         }
     }
@@ -57,6 +57,6 @@ fn main() {
     // This is diverging, so put it at the end so we don't get
     // unreachable_code errors everywhere else
     'unused_loop_label: loop {
-        //~^ WARN unused loop label
+        //~^ WARN unused label
     }
 }
diff --git a/src/test/ui/lint/unused_label.stderr b/src/test/ui/lint/unused_label.stderr
index 3e7be476e6439..31f78b28ef5e9 100644
--- a/src/test/ui/lint/unused_label.stderr
+++ b/src/test/ui/lint/unused_label.stderr
@@ -25,13 +25,13 @@ LL |         'unused_loop_label_inner_2: loop {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_label.rs:50:9
+  --> $DIR/unused_label.rs:50:5
    |
 LL |     'unused_loop_label_outer_3: loop {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_label.rs:52:5
+  --> $DIR/unused_label.rs:59:5
    |
 LL |     'unused_loop_label: loop {
    |     ^^^^^^^^^^^^^^^^^^

From 0f274122eef3c69c09c406dff32d695fca5509b3 Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Tue, 15 May 2018 20:17:20 -0700
Subject: [PATCH 05/15] Add test case for shadowed labels, with the inner
 broken multiple times

---
 src/test/ui/lint/unused_label.rs     | 26 ++++++++++++++++++++------
 src/test/ui/lint/unused_label.stderr | 19 +++++++++++++++++--
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/src/test/ui/lint/unused_label.rs b/src/test/ui/lint/unused_label.rs
index ceb70fc542dc0..f19b793546eb1 100644
--- a/src/test/ui/lint/unused_label.rs
+++ b/src/test/ui/lint/unused_label.rs
@@ -33,27 +33,41 @@ fn main() {
         break 'used_loop_label;
     }
 
-    'used_loop_label_outer_1: loop {
-        'used_loop_label_inner_1: loop {
+    'used_loop_label_outer_1: for _ in 0..10 {
+        'used_loop_label_inner_1: for _ in 0..10 {
             break 'used_loop_label_inner_1;
         }
         break 'used_loop_label_outer_1;
     }
 
-    'used_loop_label_outer_2: loop {
-        'unused_loop_label_inner_2: loop {
+    'used_loop_label_outer_2: for _ in 0..10 {
+        'unused_loop_label_inner_2: for _ in 0..10 {
             //~^ WARN unused label
             break 'used_loop_label_outer_2;
         }
     }
 
-    'unused_loop_label_outer_3: loop {
+    'unused_loop_label_outer_3: for _ in 0..10 {
         //~^ WARN unused label
-        'used_loop_label_inner_3: loop {
+        'used_loop_label_inner_3: for _ in 0..10 {
             break 'used_loop_label_inner_3;
         }
     }
 
+    // Test breaking many times with the same inner label doesn't break the
+    // warning on the outer label
+    'many_used_shadowed: for _ in 0..10 {
+        //~^ WARN unused label
+        'many_used_shadowed: for _ in 0..10 {
+            //~^ WARN label name `'many_used_shadowed` shadows a label name that is already in scope
+            if 1 % 2 == 0 {
+                break 'many_used_shadowed;
+            } else {
+                break 'many_used_shadowed;
+            }
+        }
+    }
+
     // This is diverging, so put it at the end so we don't get
     // unreachable_code errors everywhere else
     'unused_loop_label: loop {
diff --git a/src/test/ui/lint/unused_label.stderr b/src/test/ui/lint/unused_label.stderr
index 31f78b28ef5e9..e78df67794218 100644
--- a/src/test/ui/lint/unused_label.stderr
+++ b/src/test/ui/lint/unused_label.stderr
@@ -21,18 +21,33 @@ LL |     'unused_for_label: for _ in 0..10 {
 warning: unused label
   --> $DIR/unused_label.rs:44:9
    |
-LL |         'unused_loop_label_inner_2: loop {
+LL |         'unused_loop_label_inner_2: for _ in 0..10 {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
   --> $DIR/unused_label.rs:50:5
    |
-LL |     'unused_loop_label_outer_3: loop {
+LL |     'unused_loop_label_outer_3: for _ in 0..10 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
   --> $DIR/unused_label.rs:59:5
    |
+LL |     'many_used_shadowed: for _ in 0..10 {
+   |     ^^^^^^^^^^^^^^^^^^^
+
+warning: unused label
+  --> $DIR/unused_label.rs:73:5
+   |
 LL |     'unused_loop_label: loop {
    |     ^^^^^^^^^^^^^^^^^^
 
+warning: label name `'many_used_shadowed` shadows a label name that is already in scope
+  --> $DIR/unused_label.rs:61:9
+   |
+LL |     'many_used_shadowed: for _ in 0..10 {
+   |     ------------------- first declared here
+LL |         //~^ WARN unused label
+LL |         'many_used_shadowed: for _ in 0..10 {
+   |         ^^^^^^^^^^^^^^^^^^^ lifetime 'many_used_shadowed already in scope
+

From 4de4e6186417489b37bc73c064b35effe7e4409a Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Tue, 15 May 2018 20:32:43 -0700
Subject: [PATCH 06/15] Fix ignored unused outer label when inner label shadows
 and is broken multiple times

---
 src/librustc_lint/unused.rs | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index 61c0485f88615..f55a37697bc3f 100644
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -472,7 +472,7 @@ declare_lint! {
 }
 
 #[derive(Clone)]
-pub struct UnusedLabel(pub Vec<ast::Label>);
+pub struct UnusedLabel(pub Vec<(ast::Label, bool)>);
 
 impl UnusedLabel {
     pub fn new() -> Self {
@@ -493,11 +493,11 @@ impl EarlyLintPass for UnusedLabel {
             | ast::ExprKind::WhileLet(_, _, _, Some(label))
             | ast::ExprKind::ForLoop(_, _, _, Some(label))
             | ast::ExprKind::Loop(_, Some(label)) => {
-                self.0.push(label);
+                self.0.push((label, false));
             }
             ast::ExprKind::Break(Some(label), _) | ast::ExprKind::Continue(Some(label)) => {
-                if let Some(index) = self.0.iter().rposition(|&l| l.ident == label.ident) {
-                    self.0.remove(index);
+                if let Some((_, ref mut was_used)) = self.0.iter_mut().rev().find(|(l, _)| label == *l) {
+                    *was_used = true;
                 }
             }
             _ => {}
@@ -510,11 +510,9 @@ impl EarlyLintPass for UnusedLabel {
             | ast::ExprKind::WhileLet(_, _, _, Some(label))
             | ast::ExprKind::ForLoop(_, _, _, Some(label))
             | ast::ExprKind::Loop(_, Some(label)) => {
-                if let Some(unused_label) = self.0.pop() {
-                    if label.ident == unused_label.ident {
+                if let Some((_, was_used)) = self.0.pop() {
+                    if !was_used {
                         ctxt.span_lint(UNUSED_LABEL, label.ident.span, "unused label");
-                    } else {
-                        self.0.push(unused_label);
                     }
                 }
             },

From 167cedefe63b366278dbd83b533b051cd417fcf0 Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Tue, 15 May 2018 20:58:09 -0700
Subject: [PATCH 07/15] Fix formatting in unused label linting to make tidy
 checks pass

---
 src/librustc_lint/unused.rs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index f55a37697bc3f..2321d40f150e1 100644
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -496,7 +496,9 @@ impl EarlyLintPass for UnusedLabel {
                 self.0.push((label, false));
             }
             ast::ExprKind::Break(Some(label), _) | ast::ExprKind::Continue(Some(label)) => {
-                if let Some((_, ref mut was_used)) = self.0.iter_mut().rev().find(|(l, _)| label == *l) {
+                if let Some((_, ref mut was_used)) =
+                    self.0.iter_mut().rev().find(|(l, _)| label == *l)
+                {
                     *was_used = true;
                 }
             }
@@ -515,7 +517,7 @@ impl EarlyLintPass for UnusedLabel {
                         ctxt.span_lint(UNUSED_LABEL, label.ident.span, "unused label");
                     }
                 }
-            },
+            }
             _ => {}
         }
     }

From 7676982e90120cf4edacc6b1ed8a8cebce12b97c Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Thu, 17 May 2018 16:57:46 -0700
Subject: [PATCH 08/15] Revert "Add lint checks for unused loop labels"

This functionality is being reimplemented in the resolver phase

This reverts commit 503a69e844970476b27bf1ac7be951bb22194f50.
---
 src/librustc_lint/lib.rs                   |  2 -
 src/librustc_lint/unused.rs                | 58 -----------------
 src/librustc_mir/interpret/eval_context.rs |  2 +-
 src/test/ui/lint/unused_label.rs           | 76 ----------------------
 src/test/ui/lint/unused_label.stderr       | 53 ---------------
 5 files changed, 1 insertion(+), 190 deletions(-)
 delete mode 100644 src/test/ui/lint/unused_label.rs
 delete mode 100644 src/test/ui/lint/unused_label.stderr

diff --git a/src/librustc_lint/lib.rs b/src/librustc_lint/lib.rs
index b0a766ec05874..0ae133640fad9 100644
--- a/src/librustc_lint/lib.rs
+++ b/src/librustc_lint/lib.rs
@@ -110,7 +110,6 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
 
     add_early_builtin_with_new!(sess,
                                 DeprecatedAttr,
-                                UnusedLabel,
                                 );
 
     add_builtin!(sess,
@@ -178,7 +177,6 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
                     UNUSED_DOC_COMMENT,
                     UNUSED_EXTERN_CRATES,
                     UNUSED_FEATURES,
-                    UNUSED_LABEL,
                     UNUSED_PARENS);
 
     add_lint_group!(sess,
diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index 2321d40f150e1..845c964b986dd 100644
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -464,61 +464,3 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation {
         }
     }
 }
-
-declare_lint! {
-    pub(super) UNUSED_LABEL,
-    Warn,
-    "warns on unused labels"
-}
-
-#[derive(Clone)]
-pub struct UnusedLabel(pub Vec<(ast::Label, bool)>);
-
-impl UnusedLabel {
-    pub fn new() -> Self {
-        UnusedLabel(vec![])
-    }
-}
-
-impl LintPass for UnusedLabel {
-    fn get_lints(&self) -> LintArray {
-        lint_array!(UNUSED_LABEL)
-    }
-}
-
-impl EarlyLintPass for UnusedLabel {
-    fn check_expr(&mut self, _: &EarlyContext, expr: &ast::Expr) {
-        match expr.node {
-            ast::ExprKind::While(_, _, Some(label))
-            | ast::ExprKind::WhileLet(_, _, _, Some(label))
-            | ast::ExprKind::ForLoop(_, _, _, Some(label))
-            | ast::ExprKind::Loop(_, Some(label)) => {
-                self.0.push((label, false));
-            }
-            ast::ExprKind::Break(Some(label), _) | ast::ExprKind::Continue(Some(label)) => {
-                if let Some((_, ref mut was_used)) =
-                    self.0.iter_mut().rev().find(|(l, _)| label == *l)
-                {
-                    *was_used = true;
-                }
-            }
-            _ => {}
-        }
-    }
-
-    fn check_expr_post(&mut self, ctxt: &EarlyContext, expr: &ast::Expr) {
-        match expr.node {
-            ast::ExprKind::While(_, _, Some(label))
-            | ast::ExprKind::WhileLet(_, _, _, Some(label))
-            | ast::ExprKind::ForLoop(_, _, _, Some(label))
-            | ast::ExprKind::Loop(_, Some(label)) => {
-                if let Some((_, was_used)) = self.0.pop() {
-                    if !was_used {
-                        ctxt.span_lint(UNUSED_LABEL, label.ident.span, "unused label");
-                    }
-                }
-            }
-            _ => {}
-        }
-    }
-}
diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index 7b6cee96a875c..03137619edaf4 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -1705,7 +1705,7 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M
             let mut trace_text = "\n\nAn error occurred in miri:\n".to_string();
             backtrace.resolve();
             write!(trace_text, "backtrace frames: {}\n", backtrace.frames().len()).unwrap();
-            for (i, frame) in backtrace.frames().iter().enumerate() {
+            'frames: for (i, frame) in backtrace.frames().iter().enumerate() {
                 if frame.symbols().is_empty() {
                     write!(trace_text, "{}: no symbols\n", i).unwrap();
                 }
diff --git a/src/test/ui/lint/unused_label.rs b/src/test/ui/lint/unused_label.rs
deleted file mode 100644
index f19b793546eb1..0000000000000
--- a/src/test/ui/lint/unused_label.rs
+++ /dev/null
@@ -1,76 +0,0 @@
-// Copyright 2017 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.
-
-// The output should warn when a loop label is not used. However, it
-// should also deal with the edge cases where a label is shadowed,
-// within nested loops
-
-// compile-pass
-// compile-flags: -W unused-label
-
-fn main() {
-    'unused_while_label: while 0 == 0 {
-        //~^ WARN unused label
-    }
-
-    let opt = Some(0);
-    'unused_while_let_label: while let Some(_) = opt {
-        //~^ WARN unused label
-    }
-
-    'unused_for_label: for _ in 0..10 {
-        //~^ WARN unused label
-    }
-
-    'used_loop_label: loop {
-        break 'used_loop_label;
-    }
-
-    'used_loop_label_outer_1: for _ in 0..10 {
-        'used_loop_label_inner_1: for _ in 0..10 {
-            break 'used_loop_label_inner_1;
-        }
-        break 'used_loop_label_outer_1;
-    }
-
-    'used_loop_label_outer_2: for _ in 0..10 {
-        'unused_loop_label_inner_2: for _ in 0..10 {
-            //~^ WARN unused label
-            break 'used_loop_label_outer_2;
-        }
-    }
-
-    'unused_loop_label_outer_3: for _ in 0..10 {
-        //~^ WARN unused label
-        'used_loop_label_inner_3: for _ in 0..10 {
-            break 'used_loop_label_inner_3;
-        }
-    }
-
-    // Test breaking many times with the same inner label doesn't break the
-    // warning on the outer label
-    'many_used_shadowed: for _ in 0..10 {
-        //~^ WARN unused label
-        'many_used_shadowed: for _ in 0..10 {
-            //~^ WARN label name `'many_used_shadowed` shadows a label name that is already in scope
-            if 1 % 2 == 0 {
-                break 'many_used_shadowed;
-            } else {
-                break 'many_used_shadowed;
-            }
-        }
-    }
-
-    // This is diverging, so put it at the end so we don't get
-    // unreachable_code errors everywhere else
-    'unused_loop_label: loop {
-        //~^ WARN unused label
-    }
-}
diff --git a/src/test/ui/lint/unused_label.stderr b/src/test/ui/lint/unused_label.stderr
deleted file mode 100644
index e78df67794218..0000000000000
--- a/src/test/ui/lint/unused_label.stderr
+++ /dev/null
@@ -1,53 +0,0 @@
-warning: unused label
-  --> $DIR/unused_label.rs:19:5
-   |
-LL |     'unused_while_label: while 0 == 0 {
-   |     ^^^^^^^^^^^^^^^^^^^
-   |
-   = note: requested on the command line with `-W unused-label`
-
-warning: unused label
-  --> $DIR/unused_label.rs:24:5
-   |
-LL |     'unused_while_let_label: while let Some(_) = opt {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^
-
-warning: unused label
-  --> $DIR/unused_label.rs:28:5
-   |
-LL |     'unused_for_label: for _ in 0..10 {
-   |     ^^^^^^^^^^^^^^^^^
-
-warning: unused label
-  --> $DIR/unused_label.rs:44:9
-   |
-LL |         'unused_loop_label_inner_2: for _ in 0..10 {
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-warning: unused label
-  --> $DIR/unused_label.rs:50:5
-   |
-LL |     'unused_loop_label_outer_3: for _ in 0..10 {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-warning: unused label
-  --> $DIR/unused_label.rs:59:5
-   |
-LL |     'many_used_shadowed: for _ in 0..10 {
-   |     ^^^^^^^^^^^^^^^^^^^
-
-warning: unused label
-  --> $DIR/unused_label.rs:73:5
-   |
-LL |     'unused_loop_label: loop {
-   |     ^^^^^^^^^^^^^^^^^^
-
-warning: label name `'many_used_shadowed` shadows a label name that is already in scope
-  --> $DIR/unused_label.rs:61:9
-   |
-LL |     'many_used_shadowed: for _ in 0..10 {
-   |     ------------------- first declared here
-LL |         //~^ WARN unused label
-LL |         'many_used_shadowed: for _ in 0..10 {
-   |         ^^^^^^^^^^^^^^^^^^^ lifetime 'many_used_shadowed already in scope
-

From 88f4063c8320f8c0b6a9cc047887b63da1490ffb Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Thu, 17 May 2018 17:20:30 -0700
Subject: [PATCH 09/15] Reimplement unused_labels lint as a compiler builtin in
 the resolver

---
 src/librustc/lint/builtin.rs                  |  7 ++
 src/librustc_resolve/check_unused.rs          |  4 +
 src/librustc_resolve/lib.rs                   | 12 ++-
 src/test/ui/lint/unused_labels.rs             | 75 +++++++++++++++++++
 src/test/ui/lint/unused_labels.stderr         | 53 +++++++++++++
 .../ui/loops-reject-duplicate-labels-2.rs     |  1 +
 .../ui/loops-reject-duplicate-labels-2.stderr | 18 ++---
 src/test/ui/loops-reject-duplicate-labels.rs  |  1 +
 .../ui/loops-reject-duplicate-labels.stderr   | 18 ++---
 src/test/ui/suggestions/suggest-labels.rs     |  2 +-
 10 files changed, 170 insertions(+), 21 deletions(-)
 create mode 100644 src/test/ui/lint/unused_labels.rs
 create mode 100644 src/test/ui/lint/unused_labels.stderr

diff --git a/src/librustc/lint/builtin.rs b/src/librustc/lint/builtin.rs
index c55c71f85dab7..71eefec2210e4 100644
--- a/src/librustc/lint/builtin.rs
+++ b/src/librustc/lint/builtin.rs
@@ -279,6 +279,12 @@ declare_lint! {
     "detects name collision with an existing but unstable method"
 }
 
+declare_lint! {
+    pub UNUSED_LABELS,
+    Warn,
+    "detects labels that are never used"
+}
+
 /// Does nothing as a lint pass, but registers some `Lint`s
 /// which are used by other parts of the compiler.
 #[derive(Copy, Clone)]
@@ -325,6 +331,7 @@ impl LintPass for HardwiredLints {
             UNUSED_MUT,
             SINGLE_USE_LIFETIME,
             UNUSED_LIFETIME,
+            UNUSED_LABELS,
             TYVAR_BEHIND_RAW_POINTER,
             ELIDED_LIFETIME_IN_PATH,
             BARE_TRAIT_OBJECT,
diff --git a/src/librustc_resolve/check_unused.rs b/src/librustc_resolve/check_unused.rs
index 163f6a64010b5..590ce168d5d0f 100644
--- a/src/librustc_resolve/check_unused.rs
+++ b/src/librustc_resolve/check_unused.rs
@@ -142,6 +142,10 @@ pub fn check_crate(resolver: &mut Resolver, krate: &ast::Crate) {
         }
     }
 
+    for (id, span) in resolver.unused_labels.iter() {
+        resolver.session.buffer_lint(lint::builtin::UNUSED_LABELS, *id, *span, "unused label");
+    }
+
     let mut visitor = UnusedImportCheckVisitor {
         resolver,
         unused_imports: NodeMap(),
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index e13e6bc6b7456..feb5af571e435 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -1473,6 +1473,10 @@ pub struct Resolver<'a> {
     pub maybe_unused_trait_imports: NodeSet,
     pub maybe_unused_extern_crates: Vec<(NodeId, Span)>,
 
+    /// A list of labels as of yet unused. Labels will be removed from this map when
+    /// they are used (in a `break` or `continue` statement)
+    pub unused_labels: FxHashMap<NodeId, Span>,
+
     /// privacy errors are delayed until the end in order to deduplicate them
     privacy_errors: Vec<PrivacyError<'a>>,
     /// ambiguity errors are delayed for deduplication
@@ -1752,6 +1756,8 @@ impl<'a> Resolver<'a> {
             maybe_unused_trait_imports: NodeSet(),
             maybe_unused_extern_crates: Vec::new(),
 
+            unused_labels: FxHashMap(),
+
             privacy_errors: Vec::new(),
             ambiguity_errors: Vec::new(),
             use_injections: Vec::new(),
@@ -3694,6 +3700,7 @@ impl<'a> Resolver<'a> {
         where F: FnOnce(&mut Resolver)
     {
         if let Some(label) = label {
+            self.unused_labels.insert(id, label.ident.span);
             let def = Def::Label(id);
             self.with_label_rib(|this| {
                 this.label_ribs.last_mut().unwrap().bindings.insert(label.ident, def);
@@ -3742,9 +3749,10 @@ impl<'a> Resolver<'a> {
                                       ResolutionError::UndeclaredLabel(&label.ident.name.as_str(),
                                                                        close_match));
                     }
-                    Some(def @ Def::Label(_)) => {
+                    Some(Def::Label(id)) => {
                         // Since this def is a label, it is never read.
-                        self.record_def(expr.id, PathResolution::new(def));
+                        self.record_def(expr.id, PathResolution::new(Def::Label(id)));
+                        self.unused_labels.remove(&id);
                     }
                     Some(_) => {
                         span_bug!(expr.span, "label wasn't mapped to a label def!");
diff --git a/src/test/ui/lint/unused_labels.rs b/src/test/ui/lint/unused_labels.rs
new file mode 100644
index 0000000000000..86abb34658a39
--- /dev/null
+++ b/src/test/ui/lint/unused_labels.rs
@@ -0,0 +1,75 @@
+// Copyright 2017 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.
+
+// The output should warn when a loop label is not used. However, it
+// should also deal with the edge cases where a label is shadowed,
+// within nested loops
+
+// compile-pass
+
+fn main() {
+    'unused_while_label: while 0 == 0 {
+        //~^ WARN unused label
+    }
+
+    let opt = Some(0);
+    'unused_while_let_label: while let Some(_) = opt {
+        //~^ WARN unused label
+    }
+
+    'unused_for_label: for _ in 0..10 {
+        //~^ WARN unused label
+    }
+
+    'used_loop_label: loop {
+        break 'used_loop_label;
+    }
+
+    'used_loop_label_outer_1: for _ in 0..10 {
+        'used_loop_label_inner_1: for _ in 0..10 {
+            break 'used_loop_label_inner_1;
+        }
+        break 'used_loop_label_outer_1;
+    }
+
+    'used_loop_label_outer_2: for _ in 0..10 {
+        'unused_loop_label_inner_2: for _ in 0..10 {
+            //~^ WARN unused label
+            break 'used_loop_label_outer_2;
+        }
+    }
+
+    'unused_loop_label_outer_3: for _ in 0..10 {
+        //~^ WARN unused label
+        'used_loop_label_inner_3: for _ in 0..10 {
+            break 'used_loop_label_inner_3;
+        }
+    }
+
+    // Test breaking many times with the same inner label doesn't break the
+    // warning on the outer label
+    'many_used_shadowed: for _ in 0..10 {
+        //~^ WARN unused label
+        'many_used_shadowed: for _ in 0..10 {
+            //~^ WARN label name `'many_used_shadowed` shadows a label name that is already in scope
+            if 1 % 2 == 0 {
+                break 'many_used_shadowed;
+            } else {
+                break 'many_used_shadowed;
+            }
+        }
+    }
+
+    // This is diverging, so put it at the end so we don't get
+    // unreachable_code errors everywhere else
+    'unused_loop_label: loop {
+        //~^ WARN unused label
+    }
+}
diff --git a/src/test/ui/lint/unused_labels.stderr b/src/test/ui/lint/unused_labels.stderr
new file mode 100644
index 0000000000000..425b0b1769dc7
--- /dev/null
+++ b/src/test/ui/lint/unused_labels.stderr
@@ -0,0 +1,53 @@
+warning: unused label
+  --> $DIR/unused_labels.rs:18:5
+   |
+LL |     'unused_while_label: while 0 == 0 {
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: #[warn(unused_labels)] on by default
+
+warning: unused label
+  --> $DIR/unused_labels.rs:23:5
+   |
+LL |     'unused_while_let_label: while let Some(_) = opt {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: unused label
+  --> $DIR/unused_labels.rs:27:5
+   |
+LL |     'unused_for_label: for _ in 0..10 {
+   |     ^^^^^^^^^^^^^^^^^
+
+warning: unused label
+  --> $DIR/unused_labels.rs:43:9
+   |
+LL |         'unused_loop_label_inner_2: for _ in 0..10 {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: unused label
+  --> $DIR/unused_labels.rs:49:5
+   |
+LL |     'unused_loop_label_outer_3: for _ in 0..10 {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: unused label
+  --> $DIR/unused_labels.rs:58:5
+   |
+LL |     'many_used_shadowed: for _ in 0..10 {
+   |     ^^^^^^^^^^^^^^^^^^^
+
+warning: unused label
+  --> $DIR/unused_labels.rs:72:5
+   |
+LL |     'unused_loop_label: loop {
+   |     ^^^^^^^^^^^^^^^^^^
+
+warning: label name `'many_used_shadowed` shadows a label name that is already in scope
+  --> $DIR/unused_labels.rs:60:9
+   |
+LL |     'many_used_shadowed: for _ in 0..10 {
+   |     ------------------- first declared here
+LL |         //~^ WARN unused label
+LL |         'many_used_shadowed: for _ in 0..10 {
+   |         ^^^^^^^^^^^^^^^^^^^ lifetime 'many_used_shadowed already in scope
+
diff --git a/src/test/ui/loops-reject-duplicate-labels-2.rs b/src/test/ui/loops-reject-duplicate-labels-2.rs
index 598c7370b8906..b273e7a0c7c9e 100644
--- a/src/test/ui/loops-reject-duplicate-labels-2.rs
+++ b/src/test/ui/loops-reject-duplicate-labels-2.rs
@@ -18,6 +18,7 @@
 // discussed here:
 // https://internals.rust-lang.org/t/psa-rejecting-duplicate-loop-labels/1833
 
+#[allow(unused_labels)]
 pub fn foo() {
     { 'fl: for _ in 0..10 { break; } }
     { 'fl: loop { break; } }             //~ WARN label name `'fl` shadows a label name that is already in scope
diff --git a/src/test/ui/loops-reject-duplicate-labels-2.stderr b/src/test/ui/loops-reject-duplicate-labels-2.stderr
index 830270a99d112..41b4a850f1bfb 100644
--- a/src/test/ui/loops-reject-duplicate-labels-2.stderr
+++ b/src/test/ui/loops-reject-duplicate-labels-2.stderr
@@ -1,5 +1,5 @@
 warning: label name `'fl` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels-2.rs:23:7
+  --> $DIR/loops-reject-duplicate-labels-2.rs:24:7
    |
 LL |     { 'fl: for _ in 0..10 { break; } }
    |       --- first declared here
@@ -7,7 +7,7 @@ LL |     { 'fl: loop { break; } }             //~ WARN label name `'fl` shadows
    |       ^^^ lifetime 'fl already in scope
 
 warning: label name `'lf` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels-2.rs:25:7
+  --> $DIR/loops-reject-duplicate-labels-2.rs:26:7
    |
 LL |     { 'lf: loop { break; } }
    |       --- first declared here
@@ -15,7 +15,7 @@ LL |     { 'lf: for _ in 0..10 { break; } }   //~ WARN label name `'lf` shadows
    |       ^^^ lifetime 'lf already in scope
 
 warning: label name `'wl` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels-2.rs:27:7
+  --> $DIR/loops-reject-duplicate-labels-2.rs:28:7
    |
 LL |     { 'wl: while 2 > 1 { break; } }
    |       --- first declared here
@@ -23,7 +23,7 @@ LL |     { 'wl: loop { break; } }             //~ WARN label name `'wl` shadows
    |       ^^^ lifetime 'wl already in scope
 
 warning: label name `'lw` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels-2.rs:29:7
+  --> $DIR/loops-reject-duplicate-labels-2.rs:30:7
    |
 LL |     { 'lw: loop { break; } }
    |       --- first declared here
@@ -31,7 +31,7 @@ LL |     { 'lw: while 2 > 1 { break; } }      //~ WARN label name `'lw` shadows
    |       ^^^ lifetime 'lw already in scope
 
 warning: label name `'fw` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels-2.rs:31:7
+  --> $DIR/loops-reject-duplicate-labels-2.rs:32:7
    |
 LL |     { 'fw: for _ in 0..10 { break; } }
    |       --- first declared here
@@ -39,7 +39,7 @@ LL |     { 'fw: while 2 > 1 { break; } }      //~ WARN label name `'fw` shadows
    |       ^^^ lifetime 'fw already in scope
 
 warning: label name `'wf` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels-2.rs:33:7
+  --> $DIR/loops-reject-duplicate-labels-2.rs:34:7
    |
 LL |     { 'wf: while 2 > 1 { break; } }
    |       --- first declared here
@@ -47,7 +47,7 @@ LL |     { 'wf: for _ in 0..10 { break; } }   //~ WARN label name `'wf` shadows
    |       ^^^ lifetime 'wf already in scope
 
 warning: label name `'tl` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels-2.rs:35:7
+  --> $DIR/loops-reject-duplicate-labels-2.rs:36:7
    |
 LL |     { 'tl: while let Some(_) = None::<i32> { break; } }
    |       --- first declared here
@@ -55,7 +55,7 @@ LL |     { 'tl: loop { break; } }             //~ WARN label name `'tl` shadows
    |       ^^^ lifetime 'tl already in scope
 
 warning: label name `'lt` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels-2.rs:37:7
+  --> $DIR/loops-reject-duplicate-labels-2.rs:38:7
    |
 LL |     { 'lt: loop { break; } }
    |       --- first declared here
@@ -63,7 +63,7 @@ LL |     { 'lt: while let Some(_) = None::<i32> { break; } }
    |       ^^^ lifetime 'lt already in scope
 
 error: compilation successful
-  --> $DIR/loops-reject-duplicate-labels-2.rs:42:1
+  --> $DIR/loops-reject-duplicate-labels-2.rs:43:1
    |
 LL | / pub fn main() { //~ ERROR compilation successful
 LL | |     foo();
diff --git a/src/test/ui/loops-reject-duplicate-labels.rs b/src/test/ui/loops-reject-duplicate-labels.rs
index d768b002ab10c..ad24f69871c85 100644
--- a/src/test/ui/loops-reject-duplicate-labels.rs
+++ b/src/test/ui/loops-reject-duplicate-labels.rs
@@ -15,6 +15,7 @@
 // Issue #21633: reject duplicate loop labels in function bodies.
 // This is testing the exact cases that are in the issue description.
 
+#[allow(unused_labels)]
 fn foo() {
     'fl: for _ in 0..10 { break; }
     'fl: loop { break; }           //~ WARN label name `'fl` shadows a label name that is already in scope
diff --git a/src/test/ui/loops-reject-duplicate-labels.stderr b/src/test/ui/loops-reject-duplicate-labels.stderr
index a71f98b812a8c..d0cb81544f828 100644
--- a/src/test/ui/loops-reject-duplicate-labels.stderr
+++ b/src/test/ui/loops-reject-duplicate-labels.stderr
@@ -1,5 +1,5 @@
 warning: label name `'fl` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels.rs:20:5
+  --> $DIR/loops-reject-duplicate-labels.rs:21:5
    |
 LL |     'fl: for _ in 0..10 { break; }
    |     --- first declared here
@@ -7,7 +7,7 @@ LL |     'fl: loop { break; }           //~ WARN label name `'fl` shadows a labe
    |     ^^^ lifetime 'fl already in scope
 
 warning: label name `'lf` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels.rs:23:5
+  --> $DIR/loops-reject-duplicate-labels.rs:24:5
    |
 LL |     'lf: loop { break; }
    |     --- first declared here
@@ -15,7 +15,7 @@ LL |     'lf: for _ in 0..10 { break; } //~ WARN label name `'lf` shadows a labe
    |     ^^^ lifetime 'lf already in scope
 
 warning: label name `'wl` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels.rs:25:5
+  --> $DIR/loops-reject-duplicate-labels.rs:26:5
    |
 LL |     'wl: while 2 > 1 { break; }
    |     --- first declared here
@@ -23,7 +23,7 @@ LL |     'wl: loop { break; }           //~ WARN label name `'wl` shadows a labe
    |     ^^^ lifetime 'wl already in scope
 
 warning: label name `'lw` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels.rs:27:5
+  --> $DIR/loops-reject-duplicate-labels.rs:28:5
    |
 LL |     'lw: loop { break; }
    |     --- first declared here
@@ -31,7 +31,7 @@ LL |     'lw: while 2 > 1 { break; }    //~ WARN label name `'lw` shadows a labe
    |     ^^^ lifetime 'lw already in scope
 
 warning: label name `'fw` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels.rs:29:5
+  --> $DIR/loops-reject-duplicate-labels.rs:30:5
    |
 LL |     'fw: for _ in 0..10 { break; }
    |     --- first declared here
@@ -39,7 +39,7 @@ LL |     'fw: while 2 > 1 { break; }    //~ WARN label name `'fw` shadows a labe
    |     ^^^ lifetime 'fw already in scope
 
 warning: label name `'wf` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels.rs:31:5
+  --> $DIR/loops-reject-duplicate-labels.rs:32:5
    |
 LL |     'wf: while 2 > 1 { break; }
    |     --- first declared here
@@ -47,7 +47,7 @@ LL |     'wf: for _ in 0..10 { break; } //~ WARN label name `'wf` shadows a labe
    |     ^^^ lifetime 'wf already in scope
 
 warning: label name `'tl` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels.rs:33:5
+  --> $DIR/loops-reject-duplicate-labels.rs:34:5
    |
 LL |     'tl: while let Some(_) = None::<i32> { break; }
    |     --- first declared here
@@ -55,7 +55,7 @@ LL |     'tl: loop { break; }           //~ WARN label name `'tl` shadows a labe
    |     ^^^ lifetime 'tl already in scope
 
 warning: label name `'lt` shadows a label name that is already in scope
-  --> $DIR/loops-reject-duplicate-labels.rs:35:5
+  --> $DIR/loops-reject-duplicate-labels.rs:36:5
    |
 LL |     'lt: loop { break; }
    |     --- first declared here
@@ -63,7 +63,7 @@ LL |     'lt: while let Some(_) = None::<i32> { break; }
    |     ^^^ lifetime 'lt already in scope
 
 error: compilation successful
-  --> $DIR/loops-reject-duplicate-labels.rs:49:1
+  --> $DIR/loops-reject-duplicate-labels.rs:50:1
    |
 LL | / pub fn main() { //~ ERROR compilation successful
 LL | |     let s = S;
diff --git a/src/test/ui/suggestions/suggest-labels.rs b/src/test/ui/suggestions/suggest-labels.rs
index 8c97301f40b91..9fb519c57edf3 100644
--- a/src/test/ui/suggestions/suggest-labels.rs
+++ b/src/test/ui/suggestions/suggest-labels.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#[allow(unreachable_code)]
+#[allow(unreachable_code, unused_labels)]
 fn main() {
     'foo: loop {
         break 'fo; //~ ERROR use of undeclared label

From 702f1dd8469bd7710f320d48749dc1d69ffca808 Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Thu, 17 May 2018 17:32:05 -0700
Subject: [PATCH 10/15] Add tests for new labeled blocks for `unused_labels`

---
 src/test/ui/label_break_value_continue.rs     |  1 +
 src/test/ui/label_break_value_continue.stderr |  8 ++++----
 .../ui/label_break_value_unlabeled_break.rs   |  1 +
 .../label_break_value_unlabeled_break.stderr  |  4 ++--
 src/test/ui/lint/unused_labels.rs             | 15 ++++++++++++--
 src/test/ui/lint/unused_labels.stderr         | 20 ++++++++++++-------
 6 files changed, 34 insertions(+), 15 deletions(-)

diff --git a/src/test/ui/label_break_value_continue.rs b/src/test/ui/label_break_value_continue.rs
index 52e24b759d1d2..4a505dff3d467 100644
--- a/src/test/ui/label_break_value_continue.rs
+++ b/src/test/ui/label_break_value_continue.rs
@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #![feature(label_break_value)]
+#![allow(unused_labels)]
 
 // Simple continue pointing to an unlabeled break should yield in an error
 fn continue_simple() {
diff --git a/src/test/ui/label_break_value_continue.stderr b/src/test/ui/label_break_value_continue.stderr
index 24c2d1a22d01c..12a21a8a59441 100644
--- a/src/test/ui/label_break_value_continue.stderr
+++ b/src/test/ui/label_break_value_continue.stderr
@@ -1,17 +1,17 @@
 error[E0695]: unlabeled `continue` inside of a labeled block
-  --> $DIR/label_break_value_continue.rs:16:9
+  --> $DIR/label_break_value_continue.rs:17:9
    |
 LL |         continue; //~ ERROR unlabeled `continue` inside of a labeled block
    |         ^^^^^^^^ `continue` statements that would diverge to or through a labeled block need to bear a label
 
 error[E0696]: `continue` pointing to a labeled block
-  --> $DIR/label_break_value_continue.rs:23:9
+  --> $DIR/label_break_value_continue.rs:24:9
    |
 LL |         continue 'b; //~ ERROR `continue` pointing to a labeled block
    |         ^^^^^^^^^^^ labeled blocks cannot be `continue`'d
    |
 note: labeled block the continue points to
-  --> $DIR/label_break_value_continue.rs:22:5
+  --> $DIR/label_break_value_continue.rs:23:5
    |
 LL | /     'b: {
 LL | |         continue 'b; //~ ERROR `continue` pointing to a labeled block
@@ -19,7 +19,7 @@ LL | |     }
    | |_____^
 
 error[E0695]: unlabeled `continue` inside of a labeled block
-  --> $DIR/label_break_value_continue.rs:31:13
+  --> $DIR/label_break_value_continue.rs:32:13
    |
 LL |             continue; //~ ERROR unlabeled `continue` inside of a labeled block
    |             ^^^^^^^^ `continue` statements that would diverge to or through a labeled block need to bear a label
diff --git a/src/test/ui/label_break_value_unlabeled_break.rs b/src/test/ui/label_break_value_unlabeled_break.rs
index 38918da291c86..454ebd4c6cf6d 100644
--- a/src/test/ui/label_break_value_unlabeled_break.rs
+++ b/src/test/ui/label_break_value_unlabeled_break.rs
@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #![feature(label_break_value)]
+#![allow(unused_labels)]
 
 // Simple unlabeled break should yield in an error
 fn unlabeled_break_simple() {
diff --git a/src/test/ui/label_break_value_unlabeled_break.stderr b/src/test/ui/label_break_value_unlabeled_break.stderr
index 8a25975a7bda2..62c4a12231baf 100644
--- a/src/test/ui/label_break_value_unlabeled_break.stderr
+++ b/src/test/ui/label_break_value_unlabeled_break.stderr
@@ -1,11 +1,11 @@
 error[E0695]: unlabeled `break` inside of a labeled block
-  --> $DIR/label_break_value_unlabeled_break.rs:16:9
+  --> $DIR/label_break_value_unlabeled_break.rs:17:9
    |
 LL |         break; //~ ERROR unlabeled `break` inside of a labeled block
    |         ^^^^^ `break` statements that would diverge to or through a labeled block need to bear a label
 
 error[E0695]: unlabeled `break` inside of a labeled block
-  --> $DIR/label_break_value_unlabeled_break.rs:24:13
+  --> $DIR/label_break_value_unlabeled_break.rs:25:13
    |
 LL |             break; //~ ERROR unlabeled `break` inside of a labeled block
    |             ^^^^^ `break` statements that would diverge to or through a labeled block need to bear a label
diff --git a/src/test/ui/lint/unused_labels.rs b/src/test/ui/lint/unused_labels.rs
index 86abb34658a39..22b7ad4e6a7c9 100644
--- a/src/test/ui/lint/unused_labels.rs
+++ b/src/test/ui/lint/unused_labels.rs
@@ -14,6 +14,8 @@
 
 // compile-pass
 
+#![feature(label_break_value)]
+
 fn main() {
     'unused_while_label: while 0 == 0 {
         //~^ WARN unused label
@@ -67,9 +69,18 @@ fn main() {
         }
     }
 
-    // This is diverging, so put it at the end so we don't get
-    // unreachable_code errors everywhere else
     'unused_loop_label: loop {
         //~^ WARN unused label
+        break;
+    }
+
+    // Make sure unused block labels give warnings...
+    'unused_block_label: {
+        //~^ WARN unused label
+    }
+
+    // ...and that used ones don't:
+    'used_block_label: {
+        break 'used_block_label;
     }
 }
diff --git a/src/test/ui/lint/unused_labels.stderr b/src/test/ui/lint/unused_labels.stderr
index 425b0b1769dc7..d09209853e3a3 100644
--- a/src/test/ui/lint/unused_labels.stderr
+++ b/src/test/ui/lint/unused_labels.stderr
@@ -1,5 +1,5 @@
 warning: unused label
-  --> $DIR/unused_labels.rs:18:5
+  --> $DIR/unused_labels.rs:20:5
    |
 LL |     'unused_while_label: while 0 == 0 {
    |     ^^^^^^^^^^^^^^^^^^^
@@ -7,31 +7,31 @@ LL |     'unused_while_label: while 0 == 0 {
    = note: #[warn(unused_labels)] on by default
 
 warning: unused label
-  --> $DIR/unused_labels.rs:23:5
+  --> $DIR/unused_labels.rs:25:5
    |
 LL |     'unused_while_let_label: while let Some(_) = opt {
    |     ^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_labels.rs:27:5
+  --> $DIR/unused_labels.rs:29:5
    |
 LL |     'unused_for_label: for _ in 0..10 {
    |     ^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_labels.rs:43:9
+  --> $DIR/unused_labels.rs:45:9
    |
 LL |         'unused_loop_label_inner_2: for _ in 0..10 {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_labels.rs:49:5
+  --> $DIR/unused_labels.rs:51:5
    |
 LL |     'unused_loop_label_outer_3: for _ in 0..10 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_labels.rs:58:5
+  --> $DIR/unused_labels.rs:60:5
    |
 LL |     'many_used_shadowed: for _ in 0..10 {
    |     ^^^^^^^^^^^^^^^^^^^
@@ -42,8 +42,14 @@ warning: unused label
 LL |     'unused_loop_label: loop {
    |     ^^^^^^^^^^^^^^^^^^
 
+warning: unused label
+  --> $DIR/unused_labels.rs:78:5
+   |
+LL |     'unused_block_label: {
+   |     ^^^^^^^^^^^^^^^^^^^
+
 warning: label name `'many_used_shadowed` shadows a label name that is already in scope
-  --> $DIR/unused_labels.rs:60:9
+  --> $DIR/unused_labels.rs:62:9
    |
 LL |     'many_used_shadowed: for _ in 0..10 {
    |     ------------------- first declared here

From f488d2b3930c6ef07313373c119318aa509610c4 Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Thu, 17 May 2018 17:58:16 -0700
Subject: [PATCH 11/15] Remove unused label in mir

---
 src/librustc_mir/interpret/eval_context.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index 03137619edaf4..7b6cee96a875c 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -1705,7 +1705,7 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M
             let mut trace_text = "\n\nAn error occurred in miri:\n".to_string();
             backtrace.resolve();
             write!(trace_text, "backtrace frames: {}\n", backtrace.frames().len()).unwrap();
-            'frames: for (i, frame) in backtrace.frames().iter().enumerate() {
+            for (i, frame) in backtrace.frames().iter().enumerate() {
                 if frame.symbols().is_empty() {
                     write!(trace_text, "{}: no symbols\n", i).unwrap();
                 }

From a336aa91db3a21dbbe5d281ece712535b1c9ed7d Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Thu, 17 May 2018 22:17:06 -0700
Subject: [PATCH 12/15] Allow `unused_labels` in some compile-fail tests

---
 src/test/compile-fail/associated-types-outlives.rs | 1 +
 src/test/compile-fail/hygienic-label-1.rs          | 1 +
 src/test/compile-fail/hygienic-label-2.rs          | 5 ++++-
 src/test/compile-fail/hygienic-label-3.rs          | 1 +
 src/test/compile-fail/hygienic-label-4.rs          | 5 ++++-
 src/test/compile-fail/issue-27042.rs               | 1 +
 src/test/compile-fail/issue-46311.rs               | 1 +
 src/test/compile-fail/loop-break-value.rs          | 1 +
 src/test/compile-fail/loop-proper-liveness.rs      | 1 +
 src/test/compile-fail/resolve-label.rs             | 1 +
 10 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/test/compile-fail/associated-types-outlives.rs b/src/test/compile-fail/associated-types-outlives.rs
index f070ab6799c08..1b255c149ccd0 100644
--- a/src/test/compile-fail/associated-types-outlives.rs
+++ b/src/test/compile-fail/associated-types-outlives.rs
@@ -27,6 +27,7 @@ fn denormalise<'a, T>(t: &'a T) -> <T as Foo<'a>>::Bar {
 pub fn free_and_use<T: for<'a> Foo<'a>,
                     F: for<'a> FnOnce(<T as Foo<'a>>::Bar)>(x: T, f: F) {
     let y;
+    #[allow(unused_labels)]
     'body: loop { // lifetime annotations added for clarity
         's: loop { y = denormalise(&x); break }
         drop(x); //~ ERROR cannot move out of `x` because it is borrowed
diff --git a/src/test/compile-fail/hygienic-label-1.rs b/src/test/compile-fail/hygienic-label-1.rs
index 305b43402da0b..f2b8b79b099e2 100644
--- a/src/test/compile-fail/hygienic-label-1.rs
+++ b/src/test/compile-fail/hygienic-label-1.rs
@@ -13,5 +13,6 @@ macro_rules! foo {
 }
 
 pub fn main() {
+    #[allow(unused_labels)]
     'x: loop { foo!() }
 }
diff --git a/src/test/compile-fail/hygienic-label-2.rs b/src/test/compile-fail/hygienic-label-2.rs
index 24194d7bbe970..554dc190fcd3a 100644
--- a/src/test/compile-fail/hygienic-label-2.rs
+++ b/src/test/compile-fail/hygienic-label-2.rs
@@ -9,7 +9,10 @@
 // except according to those terms.
 
 macro_rules! foo {
-    ($e: expr) => { 'x: loop { $e } }
+    ($e: expr) => {
+        #[allow(unused_labels)]
+        'x: loop { $e }
+    }
 }
 
 pub fn main() {
diff --git a/src/test/compile-fail/hygienic-label-3.rs b/src/test/compile-fail/hygienic-label-3.rs
index b107b71024dad..0f819b7c6bb8e 100644
--- a/src/test/compile-fail/hygienic-label-3.rs
+++ b/src/test/compile-fail/hygienic-label-3.rs
@@ -13,6 +13,7 @@ macro_rules! foo {
 }
 
 pub fn main() {
+    #[allow(unused_labels)]
     'x: for _ in 0..1 {
         foo!()
     };
diff --git a/src/test/compile-fail/hygienic-label-4.rs b/src/test/compile-fail/hygienic-label-4.rs
index 5bfcb6360e452..9936699cb466c 100644
--- a/src/test/compile-fail/hygienic-label-4.rs
+++ b/src/test/compile-fail/hygienic-label-4.rs
@@ -9,7 +9,10 @@
 // except according to those terms.
 
 macro_rules! foo {
-    ($e: expr) => { 'x: for _ in 0..1 { $e } }
+    ($e: expr) => {
+        #[allow(unused_labels)]
+        'x: for _ in 0..1 { $e }
+    }
 }
 
 pub fn main() {
diff --git a/src/test/compile-fail/issue-27042.rs b/src/test/compile-fail/issue-27042.rs
index 23afa4b629636..79ce9fb784961 100644
--- a/src/test/compile-fail/issue-27042.rs
+++ b/src/test/compile-fail/issue-27042.rs
@@ -10,6 +10,7 @@
 
 // Regression test for #27042. Test that a loop's label is included in its span.
 
+#[allow(unused_labels)]
 fn main() {
     let _: i32 =
         'a: // in this case, the citation is just the `break`:
diff --git a/src/test/compile-fail/issue-46311.rs b/src/test/compile-fail/issue-46311.rs
index 82f55f2c14241..0815712f0670a 100644
--- a/src/test/compile-fail/issue-46311.rs
+++ b/src/test/compile-fail/issue-46311.rs
@@ -9,6 +9,7 @@
 // except according to those terms.
 
 fn main() {
+    #[allow(unused_labels)]
     'break: loop { //~ ERROR invalid label name `'break`
     }
 }
diff --git a/src/test/compile-fail/loop-break-value.rs b/src/test/compile-fail/loop-break-value.rs
index 938f7fba2a032..60478974e8042 100644
--- a/src/test/compile-fail/loop-break-value.rs
+++ b/src/test/compile-fail/loop-break-value.rs
@@ -77,6 +77,7 @@ fn main() {
     }
 
     let _: i32 = 'a: loop {
+        #[allow(unused_labels)]
         let _: () = 'b: loop {
             break ('c: loop {
                 break;
diff --git a/src/test/compile-fail/loop-proper-liveness.rs b/src/test/compile-fail/loop-proper-liveness.rs
index e411313c273b7..b53b48ee5ed93 100644
--- a/src/test/compile-fail/loop-proper-liveness.rs
+++ b/src/test/compile-fail/loop-proper-liveness.rs
@@ -32,6 +32,7 @@ fn test2() {
 fn test3() {
     let x: i32;
     // Similarly, the use of variable `x` is unreachable.
+    #[allow(unused_labels)]
     'a: loop {
         x = loop { return };
     }
diff --git a/src/test/compile-fail/resolve-label.rs b/src/test/compile-fail/resolve-label.rs
index 6695e972f3337..3d6616edbb576 100644
--- a/src/test/compile-fail/resolve-label.rs
+++ b/src/test/compile-fail/resolve-label.rs
@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#[allow(unused_labels)]
 fn f() {
     'l: loop {
         fn g() {

From 335f91fd69d70ac9c5414d310a8342daed456df3 Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Fri, 18 May 2018 07:11:44 -0700
Subject: [PATCH 13/15] Revert "Allow `unused_labels` in some compile-fail
 tests"

This reverts commit b9257e2ca161b1bf5aae9d6b667f4d0c6b8d7be6.
---
 src/test/compile-fail/associated-types-outlives.rs | 1 -
 src/test/compile-fail/hygienic-label-1.rs          | 1 -
 src/test/compile-fail/hygienic-label-2.rs          | 5 +----
 src/test/compile-fail/hygienic-label-3.rs          | 1 -
 src/test/compile-fail/hygienic-label-4.rs          | 5 +----
 src/test/compile-fail/issue-27042.rs               | 1 -
 src/test/compile-fail/issue-46311.rs               | 1 -
 src/test/compile-fail/loop-break-value.rs          | 1 -
 src/test/compile-fail/loop-proper-liveness.rs      | 1 -
 src/test/compile-fail/resolve-label.rs             | 1 -
 10 files changed, 2 insertions(+), 16 deletions(-)

diff --git a/src/test/compile-fail/associated-types-outlives.rs b/src/test/compile-fail/associated-types-outlives.rs
index 1b255c149ccd0..f070ab6799c08 100644
--- a/src/test/compile-fail/associated-types-outlives.rs
+++ b/src/test/compile-fail/associated-types-outlives.rs
@@ -27,7 +27,6 @@ fn denormalise<'a, T>(t: &'a T) -> <T as Foo<'a>>::Bar {
 pub fn free_and_use<T: for<'a> Foo<'a>,
                     F: for<'a> FnOnce(<T as Foo<'a>>::Bar)>(x: T, f: F) {
     let y;
-    #[allow(unused_labels)]
     'body: loop { // lifetime annotations added for clarity
         's: loop { y = denormalise(&x); break }
         drop(x); //~ ERROR cannot move out of `x` because it is borrowed
diff --git a/src/test/compile-fail/hygienic-label-1.rs b/src/test/compile-fail/hygienic-label-1.rs
index f2b8b79b099e2..305b43402da0b 100644
--- a/src/test/compile-fail/hygienic-label-1.rs
+++ b/src/test/compile-fail/hygienic-label-1.rs
@@ -13,6 +13,5 @@ macro_rules! foo {
 }
 
 pub fn main() {
-    #[allow(unused_labels)]
     'x: loop { foo!() }
 }
diff --git a/src/test/compile-fail/hygienic-label-2.rs b/src/test/compile-fail/hygienic-label-2.rs
index 554dc190fcd3a..24194d7bbe970 100644
--- a/src/test/compile-fail/hygienic-label-2.rs
+++ b/src/test/compile-fail/hygienic-label-2.rs
@@ -9,10 +9,7 @@
 // except according to those terms.
 
 macro_rules! foo {
-    ($e: expr) => {
-        #[allow(unused_labels)]
-        'x: loop { $e }
-    }
+    ($e: expr) => { 'x: loop { $e } }
 }
 
 pub fn main() {
diff --git a/src/test/compile-fail/hygienic-label-3.rs b/src/test/compile-fail/hygienic-label-3.rs
index 0f819b7c6bb8e..b107b71024dad 100644
--- a/src/test/compile-fail/hygienic-label-3.rs
+++ b/src/test/compile-fail/hygienic-label-3.rs
@@ -13,7 +13,6 @@ macro_rules! foo {
 }
 
 pub fn main() {
-    #[allow(unused_labels)]
     'x: for _ in 0..1 {
         foo!()
     };
diff --git a/src/test/compile-fail/hygienic-label-4.rs b/src/test/compile-fail/hygienic-label-4.rs
index 9936699cb466c..5bfcb6360e452 100644
--- a/src/test/compile-fail/hygienic-label-4.rs
+++ b/src/test/compile-fail/hygienic-label-4.rs
@@ -9,10 +9,7 @@
 // except according to those terms.
 
 macro_rules! foo {
-    ($e: expr) => {
-        #[allow(unused_labels)]
-        'x: for _ in 0..1 { $e }
-    }
+    ($e: expr) => { 'x: for _ in 0..1 { $e } }
 }
 
 pub fn main() {
diff --git a/src/test/compile-fail/issue-27042.rs b/src/test/compile-fail/issue-27042.rs
index 79ce9fb784961..23afa4b629636 100644
--- a/src/test/compile-fail/issue-27042.rs
+++ b/src/test/compile-fail/issue-27042.rs
@@ -10,7 +10,6 @@
 
 // Regression test for #27042. Test that a loop's label is included in its span.
 
-#[allow(unused_labels)]
 fn main() {
     let _: i32 =
         'a: // in this case, the citation is just the `break`:
diff --git a/src/test/compile-fail/issue-46311.rs b/src/test/compile-fail/issue-46311.rs
index 0815712f0670a..82f55f2c14241 100644
--- a/src/test/compile-fail/issue-46311.rs
+++ b/src/test/compile-fail/issue-46311.rs
@@ -9,7 +9,6 @@
 // except according to those terms.
 
 fn main() {
-    #[allow(unused_labels)]
     'break: loop { //~ ERROR invalid label name `'break`
     }
 }
diff --git a/src/test/compile-fail/loop-break-value.rs b/src/test/compile-fail/loop-break-value.rs
index 60478974e8042..938f7fba2a032 100644
--- a/src/test/compile-fail/loop-break-value.rs
+++ b/src/test/compile-fail/loop-break-value.rs
@@ -77,7 +77,6 @@ fn main() {
     }
 
     let _: i32 = 'a: loop {
-        #[allow(unused_labels)]
         let _: () = 'b: loop {
             break ('c: loop {
                 break;
diff --git a/src/test/compile-fail/loop-proper-liveness.rs b/src/test/compile-fail/loop-proper-liveness.rs
index b53b48ee5ed93..e411313c273b7 100644
--- a/src/test/compile-fail/loop-proper-liveness.rs
+++ b/src/test/compile-fail/loop-proper-liveness.rs
@@ -32,7 +32,6 @@ fn test2() {
 fn test3() {
     let x: i32;
     // Similarly, the use of variable `x` is unreachable.
-    #[allow(unused_labels)]
     'a: loop {
         x = loop { return };
     }
diff --git a/src/test/compile-fail/resolve-label.rs b/src/test/compile-fail/resolve-label.rs
index 3d6616edbb576..6695e972f3337 100644
--- a/src/test/compile-fail/resolve-label.rs
+++ b/src/test/compile-fail/resolve-label.rs
@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#[allow(unused_labels)]
 fn f() {
     'l: loop {
         fn g() {

From 5586cd80e244936283b913ab3cf0f3626eec3136 Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Fri, 18 May 2018 07:12:19 -0700
Subject: [PATCH 14/15] Revert "Remove unused label in mir"

This reverts commit b2a2450cf2925498e1c3bdd781aa1978f9eb00e5.
---
 src/librustc_mir/interpret/eval_context.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index 7b6cee96a875c..03137619edaf4 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -1705,7 +1705,7 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M
             let mut trace_text = "\n\nAn error occurred in miri:\n".to_string();
             backtrace.resolve();
             write!(trace_text, "backtrace frames: {}\n", backtrace.frames().len()).unwrap();
-            for (i, frame) in backtrace.frames().iter().enumerate() {
+            'frames: for (i, frame) in backtrace.frames().iter().enumerate() {
                 if frame.symbols().is_empty() {
                     write!(trace_text, "{}: no symbols\n", i).unwrap();
                 }

From 6da64a7666e89b39b99d728aaa3a40c124f31563 Mon Sep 17 00:00:00 2001
From: Kyle Stachowicz <kylestach99@gmail.com>
Date: Fri, 18 May 2018 16:53:39 -0700
Subject: [PATCH 15/15] Default `unused_labels` to allow, move to "unused"

---
 src/librustc/lint/builtin.rs          |  2 +-
 src/librustc_lint/lib.rs              |  1 +
 src/test/ui/lint/unused_labels.rs     | 10 ++++++++++
 src/test/ui/lint/unused_labels.stderr | 24 ++++++++++++++----------
 4 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/src/librustc/lint/builtin.rs b/src/librustc/lint/builtin.rs
index 71eefec2210e4..79b4ec61bd081 100644
--- a/src/librustc/lint/builtin.rs
+++ b/src/librustc/lint/builtin.rs
@@ -281,7 +281,7 @@ declare_lint! {
 
 declare_lint! {
     pub UNUSED_LABELS,
-    Warn,
+    Allow,
     "detects labels that are never used"
 }
 
diff --git a/src/librustc_lint/lib.rs b/src/librustc_lint/lib.rs
index 0ae133640fad9..69825027b052b 100644
--- a/src/librustc_lint/lib.rs
+++ b/src/librustc_lint/lib.rs
@@ -177,6 +177,7 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
                     UNUSED_DOC_COMMENT,
                     UNUSED_EXTERN_CRATES,
                     UNUSED_FEATURES,
+                    UNUSED_LABELS,
                     UNUSED_PARENS);
 
     add_lint_group!(sess,
diff --git a/src/test/ui/lint/unused_labels.rs b/src/test/ui/lint/unused_labels.rs
index 22b7ad4e6a7c9..23add604da6ab 100644
--- a/src/test/ui/lint/unused_labels.rs
+++ b/src/test/ui/lint/unused_labels.rs
@@ -15,6 +15,7 @@
 // compile-pass
 
 #![feature(label_break_value)]
+#![warn(unused_labels)]
 
 fn main() {
     'unused_while_label: while 0 == 0 {
@@ -55,6 +56,15 @@ fn main() {
         }
     }
 
+    // You should be able to break the same label many times
+    'many_used: loop {
+        if true {
+            break 'many_used;
+        } else {
+            break 'many_used;
+        }
+    }
+
     // Test breaking many times with the same inner label doesn't break the
     // warning on the outer label
     'many_used_shadowed: for _ in 0..10 {
diff --git a/src/test/ui/lint/unused_labels.stderr b/src/test/ui/lint/unused_labels.stderr
index d09209853e3a3..825f5e281f0b9 100644
--- a/src/test/ui/lint/unused_labels.stderr
+++ b/src/test/ui/lint/unused_labels.stderr
@@ -1,55 +1,59 @@
 warning: unused label
-  --> $DIR/unused_labels.rs:20:5
+  --> $DIR/unused_labels.rs:21:5
    |
 LL |     'unused_while_label: while 0 == 0 {
    |     ^^^^^^^^^^^^^^^^^^^
    |
-   = note: #[warn(unused_labels)] on by default
+note: lint level defined here
+  --> $DIR/unused_labels.rs:18:9
+   |
+LL | #![warn(unused_labels)]
+   |         ^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_labels.rs:25:5
+  --> $DIR/unused_labels.rs:26:5
    |
 LL |     'unused_while_let_label: while let Some(_) = opt {
    |     ^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_labels.rs:29:5
+  --> $DIR/unused_labels.rs:30:5
    |
 LL |     'unused_for_label: for _ in 0..10 {
    |     ^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_labels.rs:45:9
+  --> $DIR/unused_labels.rs:46:9
    |
 LL |         'unused_loop_label_inner_2: for _ in 0..10 {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_labels.rs:51:5
+  --> $DIR/unused_labels.rs:52:5
    |
 LL |     'unused_loop_label_outer_3: for _ in 0..10 {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_labels.rs:60:5
+  --> $DIR/unused_labels.rs:70:5
    |
 LL |     'many_used_shadowed: for _ in 0..10 {
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_labels.rs:72:5
+  --> $DIR/unused_labels.rs:82:5
    |
 LL |     'unused_loop_label: loop {
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_labels.rs:78:5
+  --> $DIR/unused_labels.rs:88:5
    |
 LL |     'unused_block_label: {
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: label name `'many_used_shadowed` shadows a label name that is already in scope
-  --> $DIR/unused_labels.rs:62:9
+  --> $DIR/unused_labels.rs:72:9
    |
 LL |     'many_used_shadowed: for _ in 0..10 {
    |     ------------------- first declared here